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Handbook

U.S. Department of Agriculture

Forest Service

Agriculture Handbook

No. 494

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USDA. National Agricultural Library

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10301 Baltimore Blvd

Beltsviile. MD 20705-2351

FIRE-WEATHER

OBSERVERS* HANDBOOK

William C. Fischer and Charles E. Hardy (Retired)

Intermountain Forest and Range Experiment Station

Missoulo/ Montana

Agriculture Handbook No. 494

U.S. Department of Agriculture Forest Service

Issued February 1976

For sale by the Superintendent of Documents, U.S. Government Printing Oflace

Washington, D.C. 20402 - Price $2.65

Stock Number 001-O00-03510-0

25% discount allowed on orders of 100 or more to one address
Fischer, William C, and Charles E. Hardy (Ret.). 197-. Fireweather observers' handbook. U.S. Dep. Agrie, Agrie. Handb.

— P./52.

Fire-weather measurements of interest are noted and the instruments used are described. Specifications for the location and layout

of a fire-weather station are given along with installation instructions for suggested equipment. Step-by-step instrument operating

and maintenance instructions are provided. Emphasis is on minimizing the major sources of error commonly associated with

weather measurement. (Formerly issued by the Intermountain

Forest and Range Experiment Station, USDA Forest Service,

Ogden, Utah, under the same title in May 1972).

The use of trade, firm, or corporation names in this publication

is for the information and convenience of the reader. Such use does

not constitute an official endorsement or approval by the U.S. Department of Agriculture of any product or service to the exclusion

of others which may be suitable.
CONTENTS

Page

INTRODUCTION 1

OBJECTIVE 1

HANDBOOK ORGANIZATION 1

Cross Reference System 2

FIRE-DANGER RATING 2

PARTI. FIRE-WEATHER MEASUREMENTS 3

CHAPTER 1. TEMPERATURE 4

1.1 INSTRUMENTS 4

Bourdon and Bimetal Thermometers , 4

Liquid-in-Glass Thermometers 4

Standard Maximum-Minimum Thermometer 5

Combined Maximum-Minimum Thermometer 6

1.2 INSTRUMENT SHELTERS 6

The Cotton Region Shelter 6

Portable Shelters 7

CHAPTER 2. RELATIVE HUMIDITY AND DEWPOINT 9

2.1 RELATIVE HUMIDITY AND DEWPOINT TABLES 9

2.2 INSTRUMENTS 9

The Psychrometer 10

Nonportable Electric Fan Psychrometer 10

Portable Electric Fan Psychrometer 10

Hand Fan Psychrometer 11

Sling Psychrometers 11

The Wet- and Dry-Bulb Hygrometer 12

The Mortarboard Psychrometer 13

2.3 THE HYGROTHERMOGRAPH 13

The Temperature Element 13

The Relative Humidity Element 14

The Chart Record 14

Reliability 15

CHAPTER 3. WIND 16

3.1 WINDSPEED 16

Contacting Anemometers 16

ni
Page

Anemometers Equipped with 1/60-Mile Contacts 17

Mechanical Counters 17

Anemometers Equipped with 1-Mile Contacts 18

The Hygrothermoaerograph 18

Anemometers Equipped with Self-Contained Readout 18

Generator Anemometers 19

Hand-held Wind Meter 20

3.2 WIND DIRECTION 21

Wind Vanes 21

CHAPTER 4. PRECIPITATION 22

4.1 INSTRUMENTS 22

The Standard 8-Inch Rain Gage 22

Types of Standard Gages 22

Measuring Sticks 23

Mounts 23

The Small Orifice Rain Gage 24

Four-Inch Clear Plastic Gage 24

Wedge-Shaped, Fencepost, or Farmer's Gage 25

The Recording Rain Gage 25

The Weighing Rain Gage 25

The Tipping Bucket Rain Gage 27

Reliability of Recording Rain Gages 27

Rain Gage Shields 28

4.2 SUPPLEMENTAL INFORMATION 28

Kind of Precipitation 28

Time Began and Ended 29

Duration 29

Snowfall Measurements 29

CHAPTER 5. FUEL MOISTURE 30

5.1 FUEL MOISTURE STICKS 30

5.2 INORGANIC FUEL MOISTURE ANALOG 30

5.3 FUEL MOISTURE SCALES 31

The Appalachian Fuel Moisture Scale 31

Chisholm Portable Fuel Moisture Scale 32

WiUiams Pocket Firestick Moisture Scale 32

Triple Beam and Harvard Balances 33

CHAPTER 6. CLOUDS 34

6.1 CLOUD FORM 34

6.2 CLOUD COVER 34

PART 2. THE FIRE-WEATHER STATION 39

CHAPTER 7. THE STANDARD FIRE-WEATHER STATION 40

7.1 LOCATION 40

7.2 EQUIPMENT LIST 40

IV
Page

7.3 LAYOUT 41

Arrangement of Equipment 41

Grounds 41

Fence 41

CHAPTER 8. INSTALLATION AND EXPOSURE OF INSTRUMENTS 42

8.1 INSTRUMENT SHELTER 42

8.2 STANDARD MAXIMUM-MINIMUM THERMOMETER 44

Townsend Support 44

Maximum Thermometer 44

Minimum Thermometer 44

8.3 ELECTRIC FAN PSYCHROMETER 44

8.4 HYGROTHERMOGRAPH 44

8.5 ANEMOMETER 45

Height Adjustment 45

Uneven Ground 45

Ground Cover 45

Nearby Obstacles 45

Installation 46

Lightning Protection 46

Lookout Tower Installation 46

Ground Installation 49

8.6 WIND COUNTER 50

Location 50

Installation 51

8.7 WIND VANE 51

Location 51

Installation 51

True North Orientation 51

8.8 STANDARD 8-INCH RAIN GAGE 52

8.9 RECORDING RAIN GAGE 52

8.10 FUEL MOISTURE STICKS 53

Duff Bed 53

Stick Exposure 53

Screening 53

8.11 FUEL MOISTURE SCALE 55

CHAPTER 9. PORTABLE, AUTOMATIC, AND REMOTE WEATHER STATIONS ... 56

9.1 PORTABLE WEATHER STATIONS 56

9.2 AUTOMATIC WEATHER STATIONS 56

9.3 REMOTE WEATHER STATIONS 57

PART 3. OPERATING INSTRUCTIONS 59

CHAPTER 10. THERMOMETERS 60

10.1 READING THERMOMETERS 60

10.2 MAXIMUM-MINIMUM THERMOMETERS 60
Page

10.3 STANDARD MAXIMUM-MINIMUM THERMOMETER 61

10.4 SIX'S COMBINED MAXIMUM-MINIMUM THERMOMETER 62

CHAPTER 11. PSYCHROMETERS 63

11.1 GENERAL OPERATING INSTRUCTIONS 63

11.2 ELECTRIC FAN PSYCHROMETER 65

11.3 PORTABLE ELECTRIC FAN PSYCHROMETER 65

11.4 HAND FAN PSYCHROMETER 66

11.5 SLING PSYCHROMETERS 66

11.6 WET-AND DRY-BULB HYGROMETER 68

11.7 THE MORTARBOARD PSYCHROMETER 69

CHAPTER 12. HYGROTHERMOGRAPHS 70

12.1 CHANGING THE CHART 70

12.2 INKING THE PENS 71

12.3 CHECKING THE CALIBRATION 71

CHAPTER 13. ANEMOMETERS 73

13.1 1/60-MILE CONTACTING ANEMOMETER 73

Readout by Reset Counter Equipped with Timer 73

Readout by Reset Counter 73

Readout by Nonreset Counter 74

Readout by Buzzer or Flasher 74

13.2 ANEMOMETERS WITH SELF-CONTAINED READOUT 74

Readout by Self-Contained Counter 74

Readout by Self-Contained Dial 74

13.3 CORRECTING WINDSPEED OBSERVATIONS TAKEN AT

HEIGHTS GREATER THAN 20-FOOT STANDARD 75

13.4 HAND-HELD WIND METER 75

CHAPTER 14. RAIN GAGES 77

14.1 THE STANDARD 8-INCH RAIN GAGE 77

Measuring Normal Amounts of Rain 77

Measuring Rain Where Measuring Tube Has Overflowed 77

Night or Early Morning Rains 77

Measuring Procedure When Ice or Snow is Expected 77

Using a Snowboard to Measure Snowfall 79

14.2 THE 4-INCH CLEAR PLASTIC GAGE 79

14.3 THE WEDGE-SHAPED GAGE 80

14.4 WEIGHING TYPE EQUIPPED WITH CLOCK DRIVE 80

Special Instructions for Use During Freezing Weather 82

CHAPTER 15. FUEL MOISTURE SCALES 83

15.1 THE APPALACHIAN SCALE 83

15.2 CHISHOLM PORTABLE SCALE 84

15.3 WILLIAMS POCKET SCALE 84

15.4 TRIPLE BEAM BALANCE 85

15.5 HARVARD BALANCE 86

VI
Page

PART 4. MAINTENANCE OF FIRE-WEATHER INSTRUMENTS 87

CHAPTER 16. THERMOMETERS 89

16.1 CLEANING 89

16.2 RESTORING WORN MARKINGS 89

16.3 THERMOMETER DEFECTS 89

Fractured Maximum Thermometers 89

Separated Columns 90

16.4 STANDARD MAXIMUM-MINIMUM THERMOMETERS EQUIPPED

WITH TOWNSEND SUPPORT 91

Annual Maintenance 91

Thermometers 91

Townsend Support 91

Periodic Maintenance 91

16.5 COMBINED (SIX'S) MAXIMUM-MINIMUM THERMOMETER 91

Annual maintenance 91

Periodic Maintenance 92

CHAPTER 17. PSYCHROMETERS 93

17.1 THE WET-BULB WICK 93

17.2 WET- AND DRY-BULB THERMOMETERS 94

17.3 CLEANING 94

17.4 ELECTRIC FAN PSYCHROMETER 94

Annual Maintenance 94

Periodic Maintenance While in Use 96

Maintenance At Least Every 2 Weeks 96

Daily Maintenance 96

Before Each Use 96

17.5 HAND FAN PSYCHROMETER 96

Annual Maintenance 96

Periodic Maintenance 97

Maintenance At Least Every 2 Weeks 97

Daily Maintenance 97

Before Each Use 97

17.6 PORTABLE ELECTRIC FAN PSYCHROMETER 97

Periodic Maintenance 97

Troubleshooting 98

17.7 MORTARBOARD PSYCHROMETER 99

Thermometers 99

Water Cup 99

Wet-Bulb Wick 99

Reflective Surface 99

17.8 SLING PSYCHROMETERS 100

Annual Maintenance 100

Periodic Maintenance 100

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Page

CHAPTER 18. HYGROTHERMOGRAPHS lOi

18.1 CLEANING . . * * ^ .^ . . 101

18.2 PEN ARM ASSEMBLIES 101

18.3 CHART DRIVE ASSEMBLY 103

18.4 CLOCK ^ ...........* 103

Bendix-Friez, Model 594 Series 104

Belfort, Catalog No. 5-594 ^^04

18.5 CALIBRATION 104

18.6 ZERO ADJUSTMENT 104

Temperature Pen 104

Relative Humidity Pen 104

18.7 RANGE ADJUSTMENT ^ * 105

Temperature Pen IO5

Relative Humidity Pen IO5

CHAPTER 19. ANEMOMETERS * . 108

19.1 CLEANING *....*..... 108

19.2 LUBRICATION ...*** . .^ ..' 108

19.3 MECHANICAL INSPECTION AND RECALIBRATION * * . . 109

19.4 CIRCUIT CHECK * * * * 110

19.5 SMALL AIRWAYS TYPE ANEMOMETER Ill

Monthly Maintenance HI

Annual Maintenance HI

Disassembly HI

Cleaning and Lubrication HI

Mechanical Inspection 112

Reassembly 112

19.6 FORESTER NO. 9X140 ANEMOMETER ......* 112

Monthly Maintenance 112

Annual Maintenance 112

Disassembly 112

Cleaning and Lubrication 112

Reassembly Hg

19.7 FORESTER MODEL 9X150 * 113

Monthly Maintenance II3

Annual Maintenance 113

Disassembly 113

Cleaning and Lubrication II4

Reassembly H^

Mechanical Inspection II4

19.8 CHISHOLM MODEL 2B3C ANEMOMETER ....**.* 114

Monthly Maintenance II4

Annual Maintenance H^

Disassembly H^

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Cleaning and Lubrication 115

Mechanical Inspection 115

Reassembly 115

19.9 STEWART ALUMINUM CUP ANEMOMETER 115

Monthly Maintenance 115

Annual Maintenance 115

Disassembly 115

Cleaning and Lubrication 115

Mechanical Inspection 115

Reassembly 116

19.10 STEWART 4-CUP ANEMOMETER 116

Monthly Maintenance 116

Annual Maintenance 116

Disassembly 116

Cleaning and Lubrication 117

Mechanical Inspection 117

Reassembly 117

19.11 BELFORT TOTALIZING ANEMOMETER 117

Monthly Maintenance 117

Annual Maintenance 118

Disassembly 118

Cleaning and Lubrication 118

Mechanical Inspection 118

Reassembly 118

19.12 FRIEZ DIAL TYPE ANEMOMETER 119

Monthly Maintenance 119

Annual Maintenance 119

Disassembly 119

Cleaning 120

Mechanical Inspection 120

Reassembly 120

Lubrication 120

19.13 WEATHER MEASURE W164 AND W164B CONTACT ANEMOMETER . . 120

Monthly Maintenance 120

Annual Maintenance 120

Disassembly 120

Cleaning and Lubrication 121

Mechanical Inspection 121

Reassembly 121

19.14 DWYER WIND METER 121

Cleaning 121

Drying 122

Removing Static 122

IX
Pí^e

Calibration 122

CHAPTER 20. WIND COUNTERS 123

20.1 BUZZERS AND FLASHERS 123

20.2 FORESTER 9X156 WIND COUNTER, MODEL 1 124

Annual Maintenance 124

Periodic Maintenance and Troubleshooting 124

20.3 HAYTRONICS TOTALIZING WIND COUNTER 124

20.4 STEWART ELECTRONIC ODOMETER 125

Annual Maintenance 125

Periodic Maintenance and Troubleshooting .- 126

CHAPTER 21. WIND VANES 127

21.1 STEWART WIND DIRECTION SYSTEM 127

Annual Maintenance 127

Wind Vane 127

Wind Direction Indicator 128

Periodic Maintenance 128

21.2 OTHER WIND DIRECTION SYSTEMS 129

CHAPTER 22. RAIN GAGES 130

22.1 NONRECORDING RAIN GAGES 130

Annual Maintenance 130

Periodic Maintenance 130

22.2 TIPPING BUCKET RAIN GAGE 131

Annual Maintenance 131

Periodic Maintenance 131

Recorder Maintenance 131

22.3 WEIGHING RAIN GAGE 132

General Maintenance 132

Calibration 132

CHAPTER 23. FUEL MOISTURE STICKS 134

CHAPTER 24. FUEL MOISTURE SCALES 135

24.1 THE APPALACHIAN SCALE 135

Annual Maintenance 135

Periodic Maintenance 136

24.2 REGION 6 SCALE 136

24.3 WILLIAMS POCKET FIRESTICK MOISTURE SCALE 136

24.4 PORTABLE FUEL MOISTURE SCALE -CHISHOLM MODEL 137

24.5 TRIPLE BEAM BALANCE 137

Annual Maintenance 137

Periodic Maintenance 137

24.6 HARVARD BALANCE 137

LITERATURE CITED 138

APPENDIX 140

INDEX 148
INTRODUCTION

As its title implies, this handbook will

serve as an important tool for the fire-weather

observer. It is equally intended, however, to

serve the needs of fire managers who are responsible for the collection of fire-weather

data and the installation and maintenance of

fire-weather stations or networks of stations.

In addition, certain portions of the handbook

have been expanded beyond strictly fireweather needs to increase its usefulness as a

general reference for land managers and forestry researchers.

OBJECTIVE

The overall objective of the handbook is to

improve both the reliability and comparability of data collected at fire-weather stations.

To accomplish this, the handbook offers uniform standards and procedures designed to

avoid, or at least minimize, the major sources

of error commonly associated with weather

measurement. These sources of error have

been identified as: (1) instrumental error;

(2) observational error; (3) exposure error;

and (4) sampling error (Smith 1970).

The standards and procedures provided to

deal with the above sources of error are consistent with well-established practices of meteorological organizations and fire control agencies.

Pubhcations of the National Weather Service

(United States); Meteorological Division, Department of Transport (Canada); World Meteorological Organization (United Nations);

USDA Forest Service; and Canada Department

of Forestry were major sources for the development of the recommended standards.

HANDBOOK ORGANIZATION

A simple recipe is proposed for avoiding, or

at least minimizing, the previously mentioned

sources of error associated with weather measurement. The four basic ingredients of this recipe provide the organizational framework for

this handbook.

The first ingredient is a knowledge of the

instruments and how they work. This is important in eliminating or minimizing all four

sources of weather measurement error. Part 1

of this handbook provides this knowledge by

briefly defining the various fire-weather measurements of concern and describing the instruments used to obtain these measurements.

Proper installation and exposure of the instruments within a properly located station is

the second major ingredient for reliable weather measurements. Adherence to standards for

the location, arrangement, installation, and exposure of weather instruments is essential if

sampling and exposure error are to be avoided.

Part 2 of the handbook provides the required

standards for proper location and layout of

fire-weather stations as well as installation and

exposure standards for the recommended instruments.

The third ingredient requires adherence to

correct instrument operating instructions in
order to minimize observational error. Part 3 of

the handbook provides step-by-step operating

instructions for the more common fire-weather

instruments.

The final ingredient in our recipe for minimizing error in weather measurement is an adequate program of continuous instrument and

station maintenance. This is a major factor in

guarding against instrument error. Part 4 of the

handbook therefore contains detailed maintenance instructions for the fire-weather instruments discussed in the preceding three parts of

the handbook.

Cross Reference System

The organizational framework described

above is, in the authors' judgment, a suitable

way to arrange the subject matter to accomplish the previously stated objective of this

handbook. The authors recognize, however,

that this type of functional organization can

create difficulties in using the handbook in reference to any one instrument. To facilitate this

type of use, a system of cross referencing is

provided following each functional discussion

of a particular weather instrument. By using

the cross reference, the reader can quickly locate additional information on the instrument

of interest in the other three sections of the

handbook.

FIRE-DANGER RATING

Traditionally, a close relationship has been

recognized between fire-weather observation

and fire-danger rating. Keetch (1966), in his

plea for quality control in fire-danger rating,

finds it imperative to establish and maintain

uniform standards of weather measurement in

order to use fire-danger ratings with confidence. More recently, Pirsko and Scowcraft

(1969) have demonstrated how fire-danger indices computed from inaccurate fire-weather

readings can result in erroneous presuppression

manning actions.

Because of this close relationship between

fire-weather observation and fire-danger rating,

the past literature on observation practices and

station standards consisted, almost exclusively,

of regional fire-danger rating handbooks. Since

the general adaption of the Spread Phase ofthe

National Fire-Danger Rating System in the

United States, these regional fire-danger rating

handbooks have gradually gone out of print.

At present, the only generally available

source of fire-weather observation information

and station standards in the United States is the

National Fire-Danger Rating System Handbook (USDA Forest Service 1964b), a part of

the Forest Service directive system. Fire people

in California have the Wildland Fire-Danger

Rating System Handbook (USDA Forest Service 1962). Both of these sources will become

obsolete when the completed National FireDanger Rating System (Deeming and Lancaster

1971) is generally adopted nationwide in 1972

or 1973. Fire-weather observation procedures

and station standards required for operation of

the completed National Fire-Danger Rating

System can be provided by this edition of the

Fire-Weather Observers Handbook.
PART 1.

^IRE-WEATHER MEASUREMENTS

A fire-weather observer will be better

equipped to obtain consistently accurate weather data if he understands something about what

he is attempting to measure and what his measurementsrepresent. It is equally important that

he understands his instruments, how they operate to provide the desired measurements, and

the level of accuracy and reliability that cíin be

expected from them.

A detailed description of the various weather elements routinely measured at fire-weather

stations is beyond the scope of this handbook.

Fire-weather observers are encouraged to study

the excellent treatment of this subject in the

Fire Weather Handbook provided by Schroeder

and Buck (1970). In the pages that follow, the

fire-weather elements of interest are simply defined and the necessary measurements are explained.

Most of the text in this part ofthe handbook

is devoted to weather instruments and how

they work. Ifthe fire manager understands how

the various instruments work, he is more likely

to install and expose them properly. By the

same token, the observer who knows his instruments is better equipped to read them correctly, and maintain them adequately. The observer should be able to recognize a faulty reading

and correct either it or the instrument immediately. In addition, the observer who knows

what makes his instrument "tick" will more

readily detect defects and recognize malfunctions.

An observer who truly understands what

he is measuring and how his instruments operate will be more likely to collect usable data;

furthermore, he may experience a high degree

of satisfaction in doing what might otherwise

be a bothersome, mechanical task.
CHAPTER 1

TEMPERATURE

Simply stated, temperature is a measure of

the degree of hotness or coldness of the air.

Temperature measurements routinely taken at

fire-weather stations are: wet-bulb temperature; dry-bulb temperature; maximum temperature; and minimum temperature. Dry-bulb

temperature at observation time is also the current temperature.

Wet- and dry-bulb temperature measurements are taken primarily to calculate relative

humidity and dewpoint and are discussed in

chapter 2 which deals with these subjects.

Maximum and minimum temperatures are

the highest and lowest temperatures occurring

during any period of time. For fire-weather

purposes, this usually is the 24-hour period preceding the scheduled afternoon observation

time. Maximum and minimum temperatures

can be used to obtain an average temperature

for the period of time they represent.

1.1 INSTRUMENTS

For fire-weather purposes, thermometers

calibrated in degrees Fahrenheit (°F.) are used

and temperatures are measured near the

ground.

These thermometers are of several types,

differing both in design and in operating principle. At fire-weather stations, liquid-in-glass

thermometers. Bourdon thermometers, and bimetal thermometers are commonly used.

Bourdon and Bimetal Thermometers

Since they are designed to change form with

corresponding changes in temperature,

Bourdon and bimetal thermometers are often

referred to collectively as ''deformation" thermometers. Deformation thermometers are

used as temperature sensing elements in dial

thermometers and hygrothermographs and are

discussed in section 2.3.

LIquld-in-Glass Thermometers

Liquid-in-glass thermometers indicate temperature by the difference in expansion between the liquid (mercury or alcohol) and the

glass bore in which the liquid is enclosed. The

bulb at the bottom of the glass bore acts as a

reservoir for the liquid which rises and falls as

temperature increases and decreases.

Mercury-filled thermometers are designed

to measure temperatures above -38° F. (the

freezing point of mercury); alcohol- or spiritfilled thermometers are designed to measure

extremely low temperatures.

Liquid-in-glass thermometers vary in length

of stem and shape of bulb. As a general rule,

long-stemmed thermometers can be read more

precisely than those with short stems. Everything else being equal, a thermometer having a

cylindrical bulb will indicate changes in air temperature faster (i.e., will have less lag time) than

one equipped with a round bulb (fig. 1.1 ).
LIQUID-IN-GLASS THERMOMETERS

I NOT TO SCALE

B

Figure 1.1. — Liquid-in^lass thermometers: A,

Mercury-filled maximum thermometer; B,

alcohol-filled minimum thermometer; C, standard

dry-bulb mercury thermometer.

Figure 1.2.— Standard maximum-minimum thermometers mounted in a Townsend Support. The

maximum thermometer is in the lower or spinning

bracket. The minimum thermometer is in the upper bracket.

Standard Maximum-Minimum Thermometer

The standard maximum-minimum

thermometer (actually two thermometers)

consists of a mercury and a spiritthermometer

fixed in a special mounting device called a

Townsend Support or spinning bracket (fig.

1.2). When properly exposed in a suitable instrument shelter, they become a very accurate

means for measuring maximum and minimum

temperatures. This instrumentis recommended

for use at all permanent fire-weather stations.

The maximum thermometer is mercuryfilled and has a small constriction in the capillary (the fine bore of the tube) just above the

bulb (fig. 1.1). As the mercury in the bulb expands with increasing temperature, some ofit is

forced past this constriction. When the temperature drops, the mercury above the constriction will not retreat into the bulb; hence, when

the bulb end of the thermometer is lowered to a

reading position, the top of the column indicates the highest temperature attained.

After being read, the thermometer is reset

by whirling in its mount. This forces the mercury through the constriction and back into the

bulb.

The mimimum thermometer is alcoholfilled and has a small glass index rod, shaped

like a dumbbell, floating in the bore (fig. 1.1).

This index can move freely in the alcohol.

When the temperature drops, the alcohol contracts and retreats down the bore. As the alcohol column contracts, it drags the index with it

by means of surface tension at the top of the

column. When the temperature again rises, the

alcohol flows past the index, leaving it at the

lowest temperature attained.

The thermometer is reset by turning it upside down in its mount until the index returns

to the "top" of the alcohol column.

The Townsend Support facilitates reading

and setting the maximum and minimum thermometers. The Support is designed for mounting on the cross board inside an instrument

shelter.

CROSS REFERENCE: Installation and Exposure 8.2; Operation 10.1-10.3; Maintenance

16.1-16.4.
Combined Maximum-Minimum Thermometer

The Six's, or combined maximum-minimum thermometer, is a U-shaped, spirit (creosote) thermometer that has a mercury column as an indicator. A metal index rod, or

dumbbell, rests at the top of the mercury

column on each side of the tube (fig. 1.3). This

index rod is pushed up the tube when the mercury column rises. The rod is left behind when

the column falls.

The scale along the left side of the U-shaped

tube is reversed; hence, the top of either mercury column always indicates current temperature. The scale along the right side of the tube

indicates maximum temperature and the scale

on the left indicates minimum temperature.

Readings for maximum and minimum temperatures are obtained at the lower edge of the appropriate index rod.

After each observation, the instrument is reset by using a small magnet to draw the metal

index rods down to the top of the mercury

columns.

Combined maximum-minimum thermometers are not as sensitive as the standard thermometers previously described; however, they

may be useful where a high degree of accuracy

is not required. The following procedures are

essential to proper operation of this instrument: periodic checking against a standard

thermometer; proper maintenance; exposure in

constant shade and free-moving air (preferably

in a suitable instrument shelter).

CROSS REFERENCE: Operation

10.1-10.2, 10.4; Maintenance 16.1-16.3, 16.5.

1.2 INSTRUMENT SHELTERS

The instrument shelter, or thermometer

screen (thermoscreen), is a specially designed

enclosure that minimizes radiant heat while allowing free movement of air past the instruments placed within. Thermometers properly

exposed in such a shelter will give temperature

readings that represent the temperature of the

surrounding outside air.

The Cotton Region Shelter

The cotton region type instrument shelter

(fig. 1.4) is standard at National Weather ServFigure 1.3.— Six's type maximum-minimum thermometer. Maximum temperature is read on the

right, minimum temperature is read on the left.

ice stations and is recommended for use at all

fire-weather stations. It is constructed of wood

and painted white both inside and out. It has a

double roof, louvered sides, and slotted openings in the floor. The shelter sits on an open

type wooden or aluminum stand. All of these

features contribute to this shelter's ability to

provide a desirable environment for the exposure of thermometers.

A variety of homemade instrument shelters

of other than cotton region design are in use at

many fire-weather stations. The continued use

of these shelters is discouraged as they complicate comparison of data between stations.

CROSS REFERENCE: Installation and Exposure 8.1.
Portable Shelters

A variety of portable instrument shelters

are used for fire-weather purposes. Some are

small wooden shelters, others are standardsized aluminum or plastic shelters. The adequacy of these shelters depends to a large

extent on shelter design, the type of instrument being used, and the required accuracy

of the data to be collected. They are not

meant to be used at permanent stations but

rather as alternatives to the cotton region

shelter at temporary field locations.

A field installation of a portable aluminum

weather shelter is shown in figure 1.5. This shelter knocks down to a compact size (fig. 1.6) for

relatively easy carrying. It has the advantage of

being full sized and of the general cotton region

design. In addition, this shelter was calibrated

against the cotton region type (USDA Forest

Service 1964a).

Figure 1.4. — Cotton region type instrument Vielter. This standard design is recommended at all fire-weather

stations.

599-270 O - 76 •
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1 H 1 - ^ . H

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--' \.,.JS*S-jai

"^

.-BSl- •

'^ ■■•*r^: .'l

..t^~:-.- :*¿:

Figure 1.5. — A portable aluminum dielter installed at a temporary field station.

Figure 1.6. — Portable aluminum instrument shelter — knocked down for easy transport to the field.
CHAPTER 2

RELATIVE HUMIDITY

AND DEWPOINT

Relative humidity (RH) is a ratio, expressed

in percent (%), of the actual amount of water

vapor in the air compared to the total amount

of water vapor necessary for saturation.

The dewpoint temperature (DP) is the temperature {° F.) at which the air, if cooled, would

reach saturation (100% RH). At this temperature, dew will start to form on a solid surface.

The dewpoint temperature and the wet- and

dry-bulb temperatures will all be equal at 100

percent relative humidity.

To more fully understand what these factors

represent and what they mean in terms of fire

weather, the reader is urged to study Countryman's (1971) excellent discussion of relative

humidity and dewpoint.

Relative humidity and dewpoint temperatures are usually recorded at least once a day at

fire-weather stations. As mentioned previously,

RH and DP are calculated from wet- and

dry-bulb temperatures at the scheduled observation time. Maximum and minimum relative

humidity are often recorded for the 24-hour

period preceding the scheduled observation

time. Maximum and minimum relative humidity is used to obtain an average relative humidity

for the period of time they represent.

2.1 RELATIVE HUMIDITY AND

DEWPOINT TABLES

Relative humidity and dewpoint values are

determined from wet- and dry-bulb temperatures by use of National Weather Service ''Relative Humidity and Dewpoint Tables," often

referred to as "psychrometric" tables. Separate

tables are provided for each of five levels of

atmospheric pressure and elevation above sea

level (table 2.1). Current National Weather

Service Relative Humidity and Dewpointtables

are enclosed in the back of this book.

Another type of relative humidity table is

based on the dry-bulb temperature and the

wet-bulb depression. The wet-bulb depression

is simply the difference in temperature between wet- and dry-bulb readings.

Table 2.1 —Selection of psychrometric tables

according to elevation above sea level

Elevation above sea level Psychrometric table

Alaska All other States Pressure

Feet --- - - Inches of mercury

0- 300 0- 500 30

301 - 1,700 501 - 1,900 29

1,701 - 3,600 1,901 - 3,900 27

3,601 - 5,700 3,901 - 6,100 25

5,701+ 6,101+ 23

2.2 INSTRUMENTS

Instruments used at fire-weather stations for

measurement of relative humidity and dewpoint are: (1) the psychrometer; (2) the wetand dry-bulb hygrometer; (3) the mortarboard

psychrometer; and (4) the hair hygrometer.

Although use varies locally, the psychrometer

is most often used for relative humidity measurement at fire-weather stations.

Psychrometers and wet- and dry-bulb hygrometers, including the mortarboard psychrometer, consist of two matched thermometers placed side-by-side on a common mounting plate. A thin cotton wick covers the bulb of

one of the thermometers. When this wick is wet
and air passes over the thermometer bulbs,

evaporation from the "wet bulb" will cause its

temperature to drop. Assuming adequate ventilation (e.g., air movement across the wet bulb),

the amount of evaporation from the wick depends on the moisture content of the surrounding air. The lower the relative humidity of the

surrounding air, the greater the evaporation

from the wet-bulb wicking; thus, a greater

spread between the wet bulb's temperature and

that of the dry bulb. The dry bulb indicates the

temperature of the surrounding air. Regardless

of the instrument used, wet- and dry-bulb readings are used to determine relative humidity percent and dewpoint temperature from standard

psychrometric tables.

The hair hygrometer indicates relative humidity by recording on a calibrated scale (dial

or chart) the changes in length of a human

hair element and the corresponding changes in

air moisture. The hair hygrometer is the humidity sensing element on hygrothermographs

(section 2.3). The hygrothermograph is widely used to obtain a continuous record of maximum and minimum relative humidities at

fire-weather stations.

The importance of adequate ventilation of

the wet bulb cannot be overemphasized in relative humidity and dewpoint determinations.

Forthisreason, artificially ventilated psychrometers are generally considered the most reliable of the four instruments mentioned.

The Psychrometer

Several types of psychrometers are used.

They differ primarily in the method of ventilating the thermometers. Psychrometers used

for fire-weather observations are: (1) the electric fan psychrometer (nonportable and portable); (2) the hand fan psychrometer; and

(3) the sling psychrometer. All types consist

of two carefully matched mercury thermometers having cylindrical bulbs and installed on

a common mounting plate. All are designed to

cool the wet bulb by forced ventilation.

Nonportable Electric Fan Psychrometer

A nonportable battery-operated electric

fan psychrometer is shown in figure 2.1.

When solidly mounted inside a suitable instrument shelter, it can provide consistently acFigure 2.1. — Electric fan psychrometer, USDA Forest Service type. This instrument is recommended

for use at all permanent fire-weather stations.

curate wet- and dry-bulb measurements. Its

use is recommended at all permanent fireweather stations. The primary advantage of

this psychrometer is that effective ventilation

is easily accomplished. Since tiresome hand

cranking or slinging is eliminated, observers

are more likely to continue ventilation until

the lowest wet-bulb reading is obtained.

CROSS REFERENCE: Installation and

Exposure 8.3; Operation 11.1-11.2; Maintenance 17.1-17.4.

Portable Electric Fan Psychrometer

The portable, battery-powered fan

psychrometer is designed for accurate determination of relative humidity and dewpoint

in any location, at any time (fig. 2.2). It is

usually supplied with a metal carrying case

containing a padded section for the psychrometer and a separate compartment for accessories and spare parts. Some other features of

this instrument include the following:

1. Fan is powered by ordinary "D" cell

flashlight batteries.

10
Figure 2.2. — Bendix "Psychron" portable electric fan psychrometer. This instrument allows accurate measurement of RH in the field.

2. Thermometers are recessed and are

shock mounted with rubber fittings.

3. A light is built in for use at night.

4. Water bottle is stored in psychrometer

housing.

5. Thermometer assembly can be removed

and used as a sling psychrometer if electrical

failure should occur.

CROSS REFERENCE: Operation

11.1-11.3; Maintenance 17.1-17.3, 17.6.

Hand Fan Psychrometer

The hand fan psychrometer is designed for

use in an instrument shelter. Except for fan

operation, it is identical to the electric fan

psychrometer (fig. 2.3). Ventilation of the

thermometers is accomplished by rapidly

hand cranking the fan. To get accurate results,

cranking must continue without interruption

until the lowest wet-bulb reading is obtained.

CROSS REFERENCE: Operation 11.1,

11.4; Maintenance 17.1-17.3, 17.5.

Sling Psychrometers

The sling psychrometer is ventilated by

whirling in a circular pattern around the hand

of the observer. Sling psychrometers come in

a variety of types (fig. 2.4). They differ mainly in the size and accuracy of the thermometers. Standard sling types are available with

12- or 9y2-inch thermometers, graduated in

F^ure 2.3. — Hand fan psychrometer, USDA Forest

Service type.

11
Figure 2.4.— Sling psychrometers. The standard

9i^-inch psychrometer (second from left) is often

kept as a "spare" at fire-weather stations.

Figure 2.5.— Wet- and dry-bulb hygrometer. The

glass reservoir on the bottom must be kept full of

water.

0.1° F., 0.5° F., or 1° F. divisions. The 91/2-

inch thermometers with 1° F. divisions £ire

more often used at fire-weather stations than

are the others. Pocket types usually have 5y2-

inch thermometers and 2° F. graduations. A

pocket sling psychrometer is provided in the

belt weather kit (USDA Forest Service 1959).

CROSS REFERENCE: Operation 11.1, 11.5;

Maintenance 17.1-17.3, 17.8.

The Wet- and Dry-Bulb Hygrometer

The wet- and dry-bulb hygrometer is designed for use in an instrument shelter exposed to free air circulation. Like the

psychrometer, the hygrometer operates on

the principle of cooling by evaporation. Ventilation, however, is meant to be accomplished by the natural movement of the surrounding air.

The instrument consists of two spherical

bulb thermometers, usually with 2° F. graduations, mounted side-by-side on a common

backing. The wet bulb is covered by a wick

which extends into a water container continually while the hygrometer is in service (fig.

2.5). Some hygrometers utilize a built-in glass

water reservoir while others make use of a

glass jar placed beneath the wet bulb. A thin

plastic oilcan with the spout cut short has

been recommended as the most desirable

water container because: (1) the water level

can be seen at a glance; (2) evaporation is reduced to a minimum; and (3) there is little

chance of it being burst with light frosts

(Williams 1964).

Relative humidity and dewpoint determinations obtained by using the wet- and

dry-bulb hygrometer generally do not approach the accuracy of those obtainable from

psychrometers due to the following:

12
1. Thermometers with 2° F. graduations

may not have a full scale accuracy of better

than ±2° F.

2. The small, spherical bulbs on the thermometers of most models tend to be sluggish

in response to atmospheric changes.

3. Airflow across the thermometers may

be inadequate if artificial ventilation is not

used.

In order to achieve the maximum accuracy

possible with the wet> and dry-bulb hygrometer, the thermometers should be fanned for

about 3 minutes prior to reading and the thermometers should be read to the nearest 1° F.

CROSS REFERENCE: Operation 11.6.

The Mortarboard Psychrometer

The mortarboard psychrometer was developed at the Southern Forest Fire Laboratory

to provide a simple, accurate, yet inexpensive

means of obtaining wet- and dry-bulb temperature readings (Taylor 1963). It consists of an

upper and lower radiation shield, a dry-bulb

thermometer, a naturally ventilated wet-bulb

thermometer, and supporting members. Water

is continuously supplied to the wet bulb by a

wick running from the wet bulb to a capped

plastic cup mounted on the lower radiation

shield (fig. 2.6).

CROSS REFERENCE: Operation 11.1,

11.7; Maintenance 17.1-17.3, 17.7.

2.3 THE HYGROTHERMOGRAPH

The hygrothermograph simultaneously and

continuously measures and records air temperature and relative humidity. Several models are in common use at fire-weather stations.

Although details of construction vary according to manufacturer, general operating principles are quite similar. All hygrothermographs

consist of four major working parts (fig. 2.7):

1. A temperature element.

2. A relative humidity element.

3. Pen arm assemblies.

4. A chart drive mechanism.

The chart drive mechanism is basically a

clock, either spring wound or battery driven,

which turns a chart-holding drum. The clock

is located either inside the drum and turns

with it or is fixed to the base of the instrument and the drum revolves around it. The

pen arm assemblies are simply the link between the chart and the temperature and humidity sensors.

The Temperature Element

The hygrothermographs that are most

commonly used today contain deformation

thermometers for measuring temperature.

Either a curved Bourdon tube or a bimetal

strip that is curved or coiled forms the

Figure 2.6. — The mortarboard psychrometer. This

instrument is widely used in the Eastern United

States.

NfFL

Figure 2.7. — The hygrothermograph. The upper pen

records temperature; the lower pen records relative

humidity.

13
Figure 2.8. — Hygrothermograph equipped with

(A) banjo ^read hair element and (B) Bourdon

Tube.

Figure 2.9. — Hygrothermograph equipped with (A)

hair bundle element and (B) bimetal strip.

temperature-sensitive element of these thermometers.

The Bourdon tube, sUghtly elliptical in

cross section, is filled to capacity with an organic fluid. One end of the tube is fixed to

the hygrothermograph base and the other to

the temperature pen arm linkage. As the temperature of surrounding air varies, the liquid

in the tube expands or contracts causing the

Bourdon tube to stretch out or curl up accordingly. These changes in form are transmitted to the chart through the pen arm linkage

system (fig. 2.8).

The bimetal strip is formed by a welding of

two different metals that have dissimilar expansion rates. As temperature of the surrounding air changes, the metals expand or

contract at different rates causing the strip to

change form. These changes in form are transmitted to the chart through the pen arm linkage system (fig. 2.9).

The Relative Humidity Element

Most hygrothermographs employ a human

hair element to measure relative humidity.

This element is usually in the form of either a

"bundle" of hairs (fig. 2.9) or a "banjo

spread" arrangement that resembles an

opened-up bracelet having cleisps on each end.

(fig. 2.8).

The operating principle of these hygrothermographs is the same; high humidity results in

a lengthening of the hair while low humidity

causes the hair to shorten. The movements of

the hairs are transmitted to the chart through

the pen arm linkage system.

The Chart Record

The temperature pen records on the upper

part of the chart and relative humidity pen on

the lower part (fig. 2.10). SeverEil temperature

chart scales are available but two are in common use: +10° to +110° F. for summer use and

- 30° to +70° F. for winter use. The relative

humidity scale covers the full range from 0 to

100 percent.

Daily, weekly, and monthly charts are

available. The chart must correspond to the

gear ratio or drum rotation of the instrument.

The gear ratio can be easily changed from

daily to weekly drum rotation, or weekly to

daily, by changing the gears on both the drum

and the arbor to correspond to the desired

chart time. Weekly charts are most often used

at fire-weather stations. To obtain a monthly

record, an additional chart drive mechanism is

usually required in addition to the required

gears.

Hygrothermograph charts have either

square or tapered ends. Only the tapered-end

charts can be used on clock cylinders that

have a vertical slot in the cylinder wall. The

ends of the chart are inserted into this slot

and held in place by a metal retainer that

presses the chart ends to the right and left

against the inside of the cylinder wall.

14
HYGRO-THERMOGRAPH

CHART NO. 5-207-W

BELFORT INSTRUMENT COMPANY

/&/ûa y

Figure 2.10. — Weekly chart record from a hygrothermograph — temperature record is on upper half of

chart; relative humidity record is on lower half.

Both square- and tapered-end charts can be

used on the more common nonslotted clock

cylinders. Both types of charts are retained by

a metal clip that holds the chart to the outer

wall of the cylinder. Although square-end

charts are most commonly used on nonslotted

cylinders, the tapered-end charts have the advantage of covering the clips that hold them

in place. This eliminates loss of data when the

cylinder is allowed to go beyond one revolution before changing charts.

Reliability

The reliability of its data depends directly

on the hygrothermograph's calibration and

maintenance. If the instrument is precisely

calibrated and given continuous maintenance,

an acceptable^ level of accuracy can be expected most of the time. This is especially

true for temperature data. Relative humidity

readings tend to be less reliable because of calibration difficulties and due to certain inherent characteristics of human hair.

A recent test (Meeks 1968) showed a rather uniform standard hygrothermograph error

ranging from ±2 to ±5 percent relative humidity. The results show that, in general, the

hygrothermograph records too low at high humidities and too high at low humidities.

Often the greatest loss of reliability in relative humidity data occurs at times of major

weather changes. At these times, loss of calibration often results from the inability of the

hairs to accommodate themselves to the new

humidity regime.

CROSS REFERENCE: Installation and

Exposure 8.4; Operation 12; Maintenance 18.

Plus or minus S percent relative humidity and ±0.5 F.

temperature (World Meteorological Organization 1969).

15
CHAPTER 3

WIND

Wind is air in motion. This motion, or velocity, has two components: windspeed and

wind direction.

Windspeed refers to the rate at which air

passes a given point. Fire-weather measurements of windspeed are expressed in statute

miles per hour (m.p.h.).

Wind direction refers to the direction from

which the wind is blowing. This direction is

recorded, often in coded form, as azimuth degrees from true north (0° to 360° ) or compass

points (N, NE, E, SE, etc.).

3.1 WINDSPEED

Fire-weather measurements of windspeed

are obtained from cup anemometers exposed

at the standard height of 20 feet above open,

level ground (fig. 3.1). This standard height

must be adjusted to compensate for height of

ground cover, surface irregularities, and nearby obstructions (see section 8.7).

Cup anemometers are calibrated to rotate

at a rate proportional to the actual windspeed. This rotation is transferred by the main

shaft to either a contacting mechanism or a

generator, depending on the type of anemometer. Either the number of contacts being made,

or voltage generated, is read out on a recording or indicating device wired to the anemometer. The readout device can be located either

at the weather station or in a nearby office.

Contacting-type anemometers are used almost exclusively at fire-weather stations.

Generator-type anemometers are commonly

used only where instantaneous readout of actual windspeed is desired.

Contacting Anemometers

Contacting anemometers consist of four

major parts: a 3- or 4-cup rotor assembly; a

main vertical shaft or spindle; a gear mechanism; and an electrical contact. In addition,

some contain a built-in dial or counter which

records and accumulates total wind movement.

Figure 3.1. — Anemometer (windspeed) and wind

vane (wind direction) exposed at 20-foot standard

he^ht at a fire-weather station.
Figure 3.2. — The small Airways anemometer with

1/60-mile contacts is used at many fire-weather

stations.

vanee of the counter indicates a closing of the

anemometer contact. The count per minute,

therefore, can be read directly as windspeed

in miles per hour.

CROSS REFERENCE: Installation and

Exposure 8.5; Operation 13.1; Maintenance

19.

Mechanical Counters

The mechanical counter is preferred over

the buzzer or flasher because the chance of

miscounting is greatly reduced, especially

when windspeed is averaged over a period of

more than a few minutes. These counters are

of three general types: nonreset; reset (fig.

3.3); and reset with 10-minute timer (fig.

3.4). The reset types can be set at zero at the

beginning of each observation and thus can be

read directly at the end of the prescribed obFigure 3.3.—Mechanical counters in use at fireweather stations: Left and center, Nonreset types;

right, reset type.

Anemometers Equipped With

1/60-Mile Contacts

The most popular contacting anemometers

are geared to close a contact after 1/60 mile

of wind passes the cups (fig. 3.2). The number

of contacts per minute, therefore, represents

the windspeed in miles per hour.

Readout is obtained by wiring a buzzer,

flasher, or more commonly, a mechanical

counter to the binding posts located on the

anemometer housing. Each buzz, flash, or adFigure 3.4. — Reset type mechanical counter with

timer simplifies determination of 10-minute average windspeed.

17
Figure 3.5. — Totalizing-type anemometers equipped with both 1/60-mile and 1-mile contacts: Left, Selfcontained dial readout; center, without self-contained readout; right, self-contained counter readout.

servation period. The reset type equipped

with a timer further simplifies the observer's

task because it records for only the period of

time desired.

CROSS REFERENCE: Installation and Exposure 8.6; Operation 13.1; Maintenance 20.

Anemometers Equipped With 1-Mile Contacts

Some anemometers have 1-mile contacts

instead of, or in addition to, l/60-müe contacts (fig. 3.5). Operation is similar to anemometers with 1/60-mile contacts except that

one contact is made for each 1 mile of wind

passing through the cups. The number of contacts per hour, therefore, gives the windspeed

in miles per hour. Usually the ninth and tenth

pins of the contact wheel are bridged to give a

longer contact for each 10 miles of wind passage. One-mile contacts are often used to obtain extended-period chart records of wind

movement. Special totalizing counters are

available for readout of anemometers with

1-mile contacts.

CROSS REFERENCE: Installation and

Exposure 8.5; Operation 13.2; Maintenance

19.1-19.4, 19.11-19.13.

The Hygrothermoaerograph

Anemometers with 1-mile contacts can be

used in conjunction with a hygrothermoaerograph to obtain a chart record of wind movement on a time scale. A hygrothermoaerograph (HTAG) is simply a conventional hygrothermograph that has been modified by the

addition of a third arm to record wind movement and temperature and relative humidity

(Fischer, Beaufait, and Norum 1969), as shown

in figure 3.6. See Appendix for wiring diagram and construction detail.

Anemometers Equipped With

Self-Contained Readout

Some anemometers are constructed with a

self-contained readout device that is driven

directly by the anemometer spindle (fig. 3.5).

This readout device may be in the form of a

counter or a dial.

In the counter type, the spindle drives a

four- or five-digit counter that indicates total wind movement. Depending on the specifications when purchased, readout will be in

statute miles, nautical miles, or kilometers.

Statute miles are used for fire-weather observations. Since the counter operates as long as

the anemometer is in service, a reading must

be taken at the beginning and ending of any

period for which data are required. To find

average windspeed, divide the elapsed count

by the elapsed time in hours.

18
pjiit—

Figure 3.6. — A hygrothermoaerograph (HTAG). Uppermost pen arm has been installed to record wind

movement.

In the dial type, the dials are composed of

two thin wheels, one rotating on top of the

other. The inner dial is graduated in tens and

hundreds of miles. The outer dial is graduated

in miles and tenths of miles (fig. 3.7).

CROSS REFERENCE: Installation and

Exposure 8.5; Operation 13.2; Maintenance

19.1-19.4, 19.11-19.13.

Generator Anemometers

Generator anemometers consist of a rotor

or cup assembly, a vertical shaft, a generator,

and a windspeed-indicating device. The shaft

connects the cups to a small permanent magnet generator. As the cups rotate, voltage is

generated in proportion to the windspeed. Instantaneous indication of the windspeed is obtained from an attached voltmeter calibrated

in terms of miles per hour (figs 3.8 and 3.9).

It is usually difficult to obtain an average

windspeed value from generator anemometers. Rough estimates can be obtained by observing a series of dial indications over a short

period and averaging the individual indications. Such estimates are not generally acceptable for fire-danger rating purposes. Average

wind data of improved accuracy can be obtained from chart records produced by some

generator anemometers. The windspeed required to start the cups rotating is relatively

high for many popular-priced generator anemometers (i.e., 5 to 6 m.p.h. compared to 2 to

3 m.p.h. for some contact types). These characteristics should be taken into consideration

when selecting instruments.

Figure 3.7. — Dial on this anemometer accumulates

total wind movement past anemometer cups.

19
Hand-Held Wind Meter

è

This highly portable venturi action wind

meter is a simple instrument designed for

quickly obtaining the approximate windspeed

close to the ground (fig. 3.10). It is accurate

within 1 or 2 miles per hour and is a component of the belt weather kit.

The slightly tapered outer plastic shell contains a double scale and a small plastic tube in

which a tiny white indicator ball is enclosed.

The action of the wind around the meter

causes the ball to rise in relation to the windspeed. The meter indicates windspeeds up to

10 m.p.h. on the low scale and up to 60

m.p.h. on the high scale.

CROSS REFERENCE: Operation 13.4;

Maintenance 19.14.

Figure 3.8. — Generator anemometer with remote

dial readout is useful whenever instantaneous

windspeed measurements are desired.

Figure 3.9. — Wind system; anemometer on left, wind

vane on right. Remote readout device ^ows windspeed (dial) and wind direction (lights).

Figure 3.10. — Hand-held wind meter provides easy

wind measurement near the ground.

20
3.2 WIND DIRECTION

Wind direction can be obtained quite simply by facing into the wind or by observing

the effect of the wind on smoke columns,

blowing dust, tree leaves, and other vegetation. Flags make good wind direction indicators and can be obtained near many fireweather stations. Colored plastic flagging tape

tied to the anemometer pole also makes a satisfactory wind direction indicator. When estimating wind direction, the observer should be

directly underneath the indicator, or as close

as possible to this position. This will minimize

errors due to perspective. The success of any

of the methods depends on the observer's

knowledge of the cardinal directions or his

use of a compass. Accuracy of observations

can be improved by establishing a north reference at each station.

Wind Vanes

The meteorological instrument, or wind

vane, used for measuring wind direction is an

asymmetrically shaped pointer or arrow

mounted on a vertical shaft (figs 3.1 and 3.9).

The arrow will turn freely in very light winds.

Many wind vanes at fire-weather stations

indicate wind direction by simply pointing into the direction of the wind. Other types of

wind vanes transmit their indications by electrical contacts, resistor circuits, etc. Readout

is usually a series of eight lamps, or dial indicators, one each representing N, NE, E, SE, S,

SW, W, and NW (fig. 3.9).

CROSS REFERENCE: Installation and Exposure 8.7; Maintenance 21.

21
CHAPTER 4

PRECIPITATION . i A

Precipitation is the amount of water falling

upon the earth as rain, snow, sleet, hail, etc. It

is measured by determining the depth, in

inches, that accumulates over a flat surface.

4.1 INSTRUMENTS

Precipitation is collected and measured in a

rain and snow gage. Most rain gages consist of

a right cylinder of known cross section, having straight sides and a sharp upper edge. This

cylinder often has an inner measuring tube in

which the amount of water can be either read

directly or measured with a graduated dipstick.

Three types of rain gages are used for fireweather measurement of precipitation:

(l)the standard 8-inch-diameter rain gage;

(2) the small orifice rain gage; and (3) the recording rain gage.

The Standard 8-Inch Rain Gage

The components of a standard-type rain

gage are shown in figure 4.1. The collector, or

top section, is 8 inches inside diameter at the

rim and is funnel-shaped at the bottom to

channel the "catch" into the measuring tube.

It also aids in reducing evaporation of collected water.

The circular area of the measuring tube is

one-tenth the area of the collector; therefore,

the depth of water within this part of the

tube magnifies the actual precipitation 10

times, allowing greater precision of measurement.

The measuring stick is marked in inches

and tenths. Each 1/10 inch on the sticks represents 0.01 inch of precipitation.

Types of Standard Gi^es

Two types of standard rain gages are available: the traditional, large capacity, rain and

snow gage (fig. 4.2); and the less expensive but

lower capacity Forest Service rain gage (fig.

4.3). As indicated, they differ primarily in capacity. The traditional type holds up to 2

inches of precipitation in its measuring tube

and a total of 20 inches in the overflow cylinder. The Forest Service type holds up to onehalf inch of precipitation in its measuring tube

and a total of 7 inches in the overflow cylinder.

Figure 4.1. — Components of the standard 8-inch rain

gage (USDA Forest Service type): A, Overflow

cylinder; B, collector; C, measuring tube;D, measuring stick.

22
Figure 4.2. — Large capacity National Weather Service standard 8-inch rain gage.

Figure 4.3. — Low capacity USDA Forest Service rain

gage was designed for use in areas of low summer

rainfall.

It was designed to provide an economical instrument for use in those areas where 24-hour

rainfall seldom exceeds a few inches.

Measurii^ Sticks

Measuring sticks of either red gum wood or

laminated plastic are used for both types of

standard gages. The plastic stick has several advantages over the wood stick: (1) water will not

creep up the stick; (2) the plastic stick and its

markings are more durable; and (3) the plastic

stick can be easily washed clean of oil, dirt, or

grease. The waterline on the wood stick, on the

other hand, is much easier to see than on the

plastic stick and since the water is more likely

to be absorbed by the wood, there is less chance

of erroneous readings due to the waterline

being displaced.

Mounts

Traditional type rain gages are mounted in

either a steel tripod stand or a wooden stand,

which is often shaped from their shipping con23

599-270 O - 76
tainer. The Forest Service rain gage is usually

mounted in a wooden stand as illustrated in

figures 4.2 and 4.3.

CROSS REFERENCE: Installation and Exposure 8.8; Operation 14.1 ¡Maintenance 22.1.

The Small Orifice Rain Gage

Rain gages designed with small openings and

reduced water storage capacities are often used

to collect supplemental rainfall data in areas

that are some distance from the main weather

station. Most of these gages are made of durable

plastic and have the advantage of low cost and

easy portability. A survey of the literature dealing with small orifice rain gages (Corbett 1967)

shows:

1. Accuracy of some gages compares favorably to the standard 8-inch rain gage.

2. Under certain conditions, a more accurate estimate of rainfall can be obtained because these gages do not obstruct the flow of

air as much as a large gage.

3. Most are unsuitable for snow measurement.

4. Use during freezing weather is not recommended.

5. Evaporation loss is relatively high ; hence,

these gages should be read as soon as possible

after precipitation ends.

Most small orifice rain gages are designed as

direct reading instruments and do not require a

measuring stick.

Several of the more common types ofsmall

orifice rain gages are shown in figures 4.4 and

4.5. Two models considered suitable for certain

fire-weather applications are described below.

Four-Inch Clear Plastic Gage

This gage is modeled after the traditional

type, 8-inch-diameter gage (fig. 4.5). It consists

of a 4-inch-diameter, knife-edged, funneled collector, an overflow cylinder, and a direct reading measuring tube. All parts are made of a

clear, durable, plastic type material. The collection tube has 0.01-inch graduations and holds 1

inch of rain; the overflow cylinder holds an additional 10 inches. The gage is supplied with a

stainless steel mounting bracket for attachment

to a post or stake.

CROSS REFERENCE: Operation 14.2;

Maintenance 22.1.

Figure 4.4. — Several types of direct reading small orifice rain gages.

F^ure 4.5. — Four-inch clear plastic direct reading

rain gage.

24
Wedge-Shaped, Fencepost, or Farmer's Gage

This unit is a smooth, one-piece molding of

durable plastic. It consists of a wedge-shaped

well on which a scale is printed (fig. 4.4). The

knife-edged opening at the top of the gage is 2.5

by 2.3 inches. The scale is graduated in units of

0.01 inch. The gage has a capacity of 6 inches of

precipitation. It is supplied with a bracket for

mounting on a post or stake. Measurement is by

direct observation of the water level in the well.

Evaporation loss can be quite high in this gage.

Both the unfunneled open top and the tendency for small amounts of water to cling to the

sides account for this high loss. The gage does

have an advantage because it will provide more

accurate measurement of small amounts ofrain

than will the 8-inch-diameter gage. However,

to capitalize on this advantage, this gage must

be read very soon after the rain stops.

CROSS REFERENCE: Operation 14.3;

Maintenance 22.1.

The Recording Rain Gage

Recording rain and snow gages provide

graphic information which can be used to determine the time duration, intensity, and

amount of precipitation for each storm or occurrence as well as the total amount of precipitation during any given time period.

There are two kinds of recording rain gages

in common use: the weighing type; and the tipping bucket type. Both consist of four main

parts: a collector; a measuring mechanism; a

recording mechanism; and a housing.

The We^hing Rain Gage

The weighing type rain gage is by far the

most widely used recording gage at fire-weather

stations. The operating principle is relatively

simple.

On the standard Fergusson type rain gage

(fig. 4.6), the knife-edged collector is 8 inches

(inside diameter) at the top and has a removable funnel at the bottom. As rain is caught by

the collector, it is funneled into a 12-quart

bucket which rests on the platform of a spring

scale weighing mechanism.

The weight of the collected precipitation entering the bucket is instantaneously transmitFigure 4.6. — Fergusson type weighing rain gage: Left, Assembled gage; righ t, weighing and recording mechanisms.

25
ted through a linkage system to the pen arm

and onto the chart (fig. 4.7). A dash pot is provided in the linkage system in order to dampen

any pen arm oscillations caused by wind or

other sources of vibration.

The pen arm records the weight of the catch

in equivalent inches of precipitation. Gages can

usually be calibrated to record a total of 2.4,6,

9, 12, or for the full capacity of 20 inches of

precipitation. Standard calibration is for 12

inches of precipitation. In this case, each inch

of record equals 1 inch of rainfall. Recording is

accomplished by a dual traverse ofthe pen arm;

the first 6 inches being recorded on the upstroke of the pen and the second 6 inches on

thedownstroke.

The spring wound chart drive is similar to

those used in hygrothermographs (see section

2.3). Like the hygrothermograph, the chart

time scale can be varied by gear selection.

Daily, weekly, and monthly intervals are normally available.

The housing encloses the entire operating

mechanism and the collector serves as the top.

A sliding door is provided at the bottom ofthe

housing for access to the chart drive and pen

arm.

The digital recording tj^je of weighii^ rain

gage operates on the same principle as the

Fergusson type, the main difference being in

the recording mechanism and the overall shape

of the gage (fig. 4.8).

The weight of precipitation caught by the

collector and deposited in the bucket is translated into a binary-decimal code and punched

on paper tape. Precipitation is recorded in

inches and tenths of inches. The tape record

can be read visually, translated manually by

using a desk reader, or converted to computer

inputs. An interval timer controls the frequency of data collection. By changing a cam, the

printout interval can be varied between 5, 6,

15, 30, and 60 minutes. At the 5-minute interval, 3 months of record can be obtained from a

roll oftape.

The gage has a total capacity of 20 inches of

precipitation. Both a.c. and d.c. powered units

are normally available.

CROSS REFERENCE: Installation and

Exposure 8.9; Operation 14.4; Maintenance

22.3.

F^ure 4.7. — Weighing rain gage chart record. The

first 6 inches of rain is recorded on upper traverse

of pen.

Figure 4.8. — Digital recordii^ rain gage equipped

with Alter shield.

26
The TippingBucket Rain Gage

The tipping bucket rain gage (fig. 4.9) is

used primarily for remotely recording precipitation. Both 8-inch- and 12-inch-diameter

models Eire available.

The operating principle of the tipping

bucket gage is relatively simple. Precipitation is

funneled from the collector through a small

spout to a tipping bucket mechanism. The tipping bucket mechanism consists of two small

buckets, each having a capacity of 0.01 inch of

precipitation (fig. 4.10). The bucket under the

spout fills to capacity, loses its balance, and

tips. As the bucket tips, it closes a mercury

switch which sends an electric impulse, representing 0.01 inch of precipitation, to a remotely located recorder. As the loaded bucket tips,

the second bucket is positioned under the

spout. The water from the tipping bucket is

emptied into an overflow reservoir.

Several types of recorders can be used with

the tipping bucket gage. The most popular is

the spring-wound or battery-operated, clock

driven, event recorder. The chart record shows

precipitation by a stepped trace; each step represents 0.01 inch, or one tip of the bucket.

After 1 inch of precipitation has been recorded,

the pen drops to the bottom of the chart and

starts a new trace. Some event recorders are

equipped with a digital counter which shows

total accumulated precipitation at a glance.

CROSS REFERENCE: Installation and Exposure 8.9; Maintenance 22.2.

Reliability ofRecording Rain Gages

Observers are often perplexed when they encounter differences in catch between a recording rain gage and a nearby nonrecording gage;

however, such differences are not unusual.

Studies show that recording gages equipped

with sloping shoulders below the collector orifice will collect from 2 to 6 percent less precipitation than the standard nonrecording gage that

has the shape of a right cylinder (Jones 1969).

Aside from collector shape or size of opening, the tipping bucket gage has additional features that can affect the reliability of catch

data. During light rains in warm weather, water

can accumulate in the receiving bucket slowly

enough to allow losses from evaporation before

Figure 4.9. — Tipping bucket rain gage.

-#SP.'*

Figure 4.10. — Tipping bucket is visible inside the inspection door.

27
F^ure 4.11. — Alter type rain gage shield mounted

around a precipitation storage gage.

enough rain is collected to tip the bucket. In

very heavy rainfall, some water loss can occur

during the tipping operation;that is, more than

0.01 inch can be deposited in the tipping

bucket before the empty bucket is in position

to start receiving the steady stream of water.

Rain Gage Shields

Rain gages are often installed in situations

where the effects of wind on precipitation

catch cannot be minimized by site selection

(see section 7.1). In such cases, a rain gage

shield may be required. Two types of shields

are in common use:

1. The trumpet-shaped Nipher type which

attaches to the top of the rain gage, and

2. The Alter type which consists of a series

of individual free-swinging baffles on a large

steelring(figs. 4.8 and 4.11). The Alter type has

its own supports and is installed around the

rain g£ige.

Both types of shields can successfully minimize the effects of wind on rainfall catch. Snow

will often build up around the Nipher type

shield, however, causing blockage of the rain

gage opening. Because of this, the Alter type

shield is highly favored at year-round stations

in snow country.

The routine use of rain gage shields at fireweather stations would improve the accuracy

of precipitation catch. Some meteorologists believe that the most serious observational error

at weather stations is caused by not using rain

gage shields.

4.2 SUPPLEMENTAL

INFORMATION

In addition to the amount of precipitation

collected in the rain gage, the following supplemental information should be considered part

of a complete precipitation record :

1. Kind of precipitation.

2. Time began.

3. Time ended.

4. Duration.

5. Snowfall measurements — if year-round

station.

Kind of Precipitation

The kind of precipitation refers to whether

28
it was drizzle, rain, snow, sleet, or hail. This

information is often entered in coded form on

the record sheet.

Time Began and Ended

The beginning and ending time of each continuous precipitation occurrence should be

recorded, usually to the nearest hour. A

recording rain gage is a ready source for this

type of information.

Duration

The duration of precipitation refers to the

elapsed time from beginning to end of each occurrence. Usually the sum of the elapsed times

for all occurrences during the reporting period

is entered.

Snowfall Measurements

Snowfall is the amount of new snow that has

fallen during the recording interval (usually 24

hours). Measurements normally required are

snow depth and water equivalent. Often the

total accumulated depth is also desired. This

total depth is sometimes obtained by simply

reading the depth against a snow stake (fig.

4.2).

If snowfall is being measured for official climatological records or for special studies, procedures that are more detailed than those discussed here will be required. The National

Weather Service provides such detailed procedures (U.S. Department of Commerce, ESSA

1970).

Snowfall is the depth of the new snow measured in inches and tenths of inches. Water equivalent is the water content of the new snow

that is measured in inches and tenths of inches

in the same way that rain is measured.

The standard 8-inch rain gage, from which

collector and measuring tube have been removed, can be used to measure both depth of

new snow and water equivalent. This method

should be used only where a high degree of

accuracy is not required. Wind can have a significant effect on the amount of snow caught by

the gage as well as the level of the snow in the

gage. When accumulated snow depths are greater than the height of the rain gage, or when a

higher degree of accuracy is desired, a snowboard should be used.

The snowboard is a wooden or plastic board

about 4 feet square. It should be mounted level,

either on or close to the ground in a protected

opening. One-half of the board is cleared after

each snowfall, the other half is left undisturbed. The depth and water equivalent of the

new snow, as well as the total depth of the

accumulated snow (old and new), are measured.

Like other methods of snow measurement,

this method is wind sensitive. Every effort

should be made to locate the snowboard in an

area that obtains representative snowfall but is

sheltered from the wind. If wind is allowed to

blow across the snowboard, part of the old

snow on the board could blow or drift onto the

other half.

CROSS REFERENCE: Installation and Exposure 8.9; Operation 13.1, 13.4.

29
CHAPTER 5

FUEL MOISTURE

Since Gisborne (1933) first developed the

idea in 1924, fuel moisture indicator sticks, or

similar types of analogs, have been widely used

to estimate the moisture content of small forest

fuels.

5.1 FUEL MOISTURE STICKS

A fuel moisture indicator stick is "... a specially prepared stick or set of sticks of known

dry weight continuously exposed to the weather and periodically weighed to determine

changes in moisture content as an indication of

moisture change in forest fuels" (Society of

American Foresters 1958). Unlike conventional weather instruments, indicator sticks do not

measure any single weather variable but rather

they "... measure the net effect of climatic

factors affecting flammability in terms of the

most significant item, the fuel itself." (Davis

1959). For this reason, the practice of using

fuel moisture indicator sticks, or some other

analog of fuel moisture, is common at fireweather stations, both in conjunction with fire

rating systems and prescribed burning operations.

A standard fuel moisture indicator stick

consists of four 1/2-inch ponderosa pine sapwood dowels spaced one-fourth inch apart on

two 3/16-inch-diameter hardwood pins. The

dowels are held in place on the pins by wire

brads at each intersection. The resultant indicator stick (fig. 5.1) is 2% inches wide, about

20 inches long, and has an ovendry weight of

100 grams. A screw hook inserted in the end of

one of the dowels and the notation, "This end

NORTH, this side up" is stamped just below

the screw hook in the surface of the dowel

(Hardy 1953).

CROSS REFERENCE: Installation and Exposure 8.10; Operation 15; Maintenance 23.

5.2 INORGANIC FUEL MOISTURE

ANALOG

The wooden fuel moisture stick has several

important shortcomings as an analog of fuel

moisture.^

Michael A. Fosberg. Analogs for fuel moisture determination in National Fire Danger Rating. Unpublished report

on file at Rocky Mountain Forest and Range Experiment

Station, Fort Collins, Colorado 80521. Office Report 2106-5,

September 2, 1971.

1

Figure 5.1. — One-half-inch ponderosa pine fuel moisture indicator sticks and wire mounting rack (two

required per installation).

30
1. The response characteristics of wood are

highly variable. Dowels cut from the same

board will often give different fuel moisture

values when exposed side by side in the same

environment.

2. Exposure and aging can change both the

response characteristics and the calibration of a

wooden stick. Discoloration with age changes

the radiation characteristics of the stick. If the

dowels check and split as they often will, more

surface area is exposed to the air and the calibration of the stick is changed. The actual

weight or mass of the stick can be reduced if

splitting and checking are severe.

Work currently in progress will produce an

analog made of an inorganic substance which

will overcome the deficiencies of the wooden

fuel moisture stick. The final product will have

the following attributes:

1. It will be reproducible. Each analog will

respond exactly the same as all others.

2. It will be constructed to respond in a

manner similar to dead forest fuels.

3. Analogs of different size and shape will

be produced so that other than fine dead fuels

can be evaluated.

4. Electric readout will be provided so that

values can be obtained at a glance from an attached dial or chart record.

When development is completed and they

become generally available, the inorganic fuel

moisture analog will replace the fuel moisture

stick at fire-weather stations.

5.3 FUEL MOISTURE SCALES

The weight, in excess of ovendry weight

(100 grams for a 1/2-inch ponderosa pine stick)

of a properly exposed analog represents fuel

moisture. Fuel moisture analogs can be measured, therefore, by weighing them on a suitable

scale. Several such scales in common use are:

the Appalachian scale; the Chisholm type portable scale; and the Williams pocket scale. All of

these scales were developed specifically to

weigh fuel moisture indicator sticks. Standard

laboratory balances, especially the triple beam

balance and the Harvard balance, are also used

to weigh fuel moisture sticks.

The Appalachian Fuel Moisture Scale

The Appalachian fuel moisture scale is preferred over two-pan (HarvEird balance) and

triple beam balances for obtaining fuel moisture stick weights (fig. 5.2) at fire-weather stations. Byram (1940) designed the Appalachian

scale specifically for measurement of basswood

slats, which were similar in purpose to fuel

sticks but had variable ovendry weights. It consists of a pivoted balance arm mounted on a 10-

by 10-inch metal back. A sliding weight on the

arm is used to adjust the scale for the ovendry

weight of the analog. The stick, or other analog,

is hung on a small hook at the left end of the

balance arm when weighed. The pointed right

end of the balance arm indicates the moisture

content of the analog on a curved scale graduated from 0 to 50 percent. A standard

100-gram weight is provided to level and zero

the scale.

The Appalachian scale shelter (Barney

1962) was designed to insure correct leveling of

the scale and facilitate the weighing of fuel

moisture sticks. It provides for adjustment in

two planes, adequate room inside, and ample

viewing uhrough a large window in the door

(fig. 5.2).

CROSS REFERENCE: Installation and Exposure 8.11; Operation 15.1; Maintenance

24.1.

Figure 5.2. — Appalachian fuel moisture scale

mounted in Appalachian scale shelter.

31
Chisholm Portable Fuel Moisture Scale

This scale works in the same manner as the

Appalachian scale except that it has no adjustment for a range of ovendry weights. It is calibrated to use the 100-gram, ovendry weight,

1/2-inch stick (fig. 5.3). Although it can be

hand held, it is much easier to use if it can be

hung on a post, tree, truck, or similar support.

A 100-gram test weight is provided with the

scale.

CROSS REFERENCE: Operation 15.2;

Maintenance 24.4.

Williams Pocket Firestick

Moisture Scale

This is a very portable, accurate, and durable

scale (fig. 5.4). It is iy2 inches in diameter and

less than 5 inches long. It weighs 14 ounces.

The case weighs 100 grams and doubles as a

calibration weight. The graduations are read in

direct percentage of the amount of moisture in

100 grams of wood. The scale is sensitive to

one-fourth gram. Micrometer graduations are

read up to 25 percent.

CROSS REFERENCE: Operation 15.3;

Maintenance 24.3. Figure 5.3. — Portable fuel moisture scale.

Figure 5.4. — Portable firestick moisture scale: Left, Assembled for storage; right, assembled for use.

32
Figure 5.5. — Three models of the triple beam balance.

Figure 5.6. — The Harvard balance.

Triple Beam and Harvard Balances

These are standard laboratory balances. The

triple beam balance has a single pan (fig. 5.5)

and the Harvard balance a double pan (fig. 5.6).

Fuel stick weight is read from the scales after

balance has been achieved.

When used at fire-weather stations, triple

beam and Harvard balances are installed in a

scale shelter similar to that shown in figure 5.7.

It is important that the shelter be watertight,

firmly mounted, and exactly level and plumb.

CROSS REFERENCE: Installation and Exposure 8.11; Operation 15.4; 15.5; Maintenance 24.5, 24.6.

Figure 5.7. — Scale shelter for triple beam balance or

Harvard balance.

, 44 I

33
CHAPTER 6

CLOUDS

A cloud is a visible aggregate of minute particles of water or ice, or both, in the free air. This

aggregate may include larger particles of water

and ice and nonaqueous liquid or solid particles,

such as those present in fumes, smoke, or dust

(World Meteorological Organization 1956).

Forfire-weather purposes, cloud observation

usually consists of identifying and recording

the cloud form and amount of cloud cover.

6.1 CLOUD FORM

Clouds are constantly changing, hence they

exhibit an endless variety of forms. For classification purposes, however, only a few characteristic cloud forms are recognized. The ''International System" for cloud classification lists 10

major cloud forms (genera) within three height

classes (families). Several species are recognized

within each genus. The system provides for further breakdown of cloud forms (varieties, supplementary features, etc.) but these are rarely

needed for fire-weather purposes. Identification as to genus is usually sufficient for all

except clouds that have vertical development.

These require species identification in order to

indicate stage of development. Often, fireweather observers are only required to record

the vertical clouds because of their importance

as lightning producers and indicators of atmospheric stability.

A simplified cloud classification for fireweather purposes is presented in table 6.1.

Characteristic cloud forms are illustrated in figure 6.1. Observers are urged to obtain current

editions of the National Weather Service Cloud

Form charts to supplement the illustrations in

figure 6.1.

6.2 CLOUD COVER

Cloud cover refers to the amount (in tenths)

of the sky which is covered by clouds or hidden

by surface-based obscuring phenomena such as

smoke or fog.

The following average cloud cover classification is sufficient for most fire-weather purposes:

Clear. — Sky is cloudless or the cloud cover

averages less than one-tenth (to the nearest

tenth).

Scattered clouds. — An average of one-tenth

through five-tenths of the sky is covered with

clouds.

Broken clouds. — An average of six-tenths

through nine-tenths of the sky is covered by

clouds.

Overcast. — An average of more than ninetenths of the sky is covered by clouds.

Obscured. — Sky is completely hidden by

surface-based obscuring phenomena such as

fog, smoke, smog, or overcast.

34
Table 6.1. —A simplified cloud classification for fire-weather purposes

CO

CJ1

Family Genus Species Abbreviation Description

HIGH CLOUDS

16,500 to

Cirrus Ci Wispy, hair-like clouds. Formed of delicate filaments, patches, narrow

bands, or feather-like plumes.

45,000 feet Cirrocumulus Ce Thin, white, grainy, and rippled patches or sheets or layers. Show very

slight vertical development in the form of turrets and shallow towers.

Cirrostratus Cs Transparent, hair-like or smooth whitish veil. Covers all or part of the

sky. Produces halo phenomenon.

MIDDLE CLOUDS

6,500 to

Altocumulus Ac Extensive sheet of regularly arranged white and gray, somewhat rounded

cloudlets.

23,000 feet Altocumulus

castellanus

Ac cas Altocumulus with vertical development in the form of small towers or

turrets. Elements have a common horizontal base and appear to be

arranged in lines.

Altocumulus

lenticularis

Ac len A patch of altocumulus in the shape of a lens or almond. Often

stationary and very elongated with well-defined outlines.

Altostratus As Grayish or bluish sheet or layer covering all or part of the sky. Sun

may show vaguely but no halo.

Nimbostratus Ns Dark, gray cloud layer thick enough to blot out the sun. Continuous rain

or snow; without lightning.

LOW CLOUDS

Surface to

Stratocumulus Sc Gray and whitish layer with dark patches formed of nonfibrous rounded

masses or rolls. Like altocumulus but lower. May have virga at base.

6,500 feet Stratus St Gray layer with uniform base which may give drizzle. When sun is visible

through cloud, its outline is clearly discernible.

T

H

E

V

E

R

T

I

C

A

L

C

L

O

U

D

S

Cumulus Cu Detached clouds, generally dense and sharply outlined. Developing vertically

in the form of rising mounds, domes, or towers. Brilliant white in sunlight.

Base is dark and nearly horizontal.

Cumulus

humilis

Cu hum Fair weather cumulus with Uttle vertical extent; generally appear

flattened.

Cumulus

congestus

Cu con Towering cumulus with strong vertical extent in the form of domes or

towers. May be accompanied by other cumulus or stratocumulus with

bases at same level.

Cumulonimbus Cb Heavy and dense cloud with considerable vertical extent, in the form of a

mountain or huge towers. The upper part usually smooth, sometimes fibrous,

with top flattened to anvil shape or vast cirrus plume. Produces lightning,

hail, tornadoes, heavy rain, and high winds.

Cumulonimbus

calvus

Cbcal Cumulonimbus without anvil. Any tower development lacks sharp outlines. May have rain or virga at base.

Cumulonimbus

capHiatus

Cbcap Cumulonimbus with anvil-shaped top. Top may also be in the form of a

plume, or a vast more or less disorderly mass of hair. Top may extend

to 40,000 feet or more. May have rain or virga at base. Produces

lightning, hail, heavy rain, and high winds.
FORMS

FAMILY

A

HIGH CLOUDS

16500 to 45000 feet

1. CIRRUS

2. CIRROCUMULUS

3. CIRROSTRATUS

.»diHH ihi- -kv. Ç.f

veil d'les n->t

¡ib"««- Ihr hoi'iïoi

Cirrus-irflcn m rurviiqiins:

hjni(--i and Clriu-sli-jiu^

or (■■i-rr.,str.iius a!'>nc: in

FAMILY MIDDLE CLOUDS

"D 6500 to 23000 feet

4. ALTOCUMULUS

5. ALTOSTRATUS

6. NIMBOSTRATUS

iMl Thin

altostratus

thi'tfUflh thi^ jiart tht- ;i

.IS thruuKh ^r:<un(l f;!».-'

Itocumulus

ed irom n^ cumulus

uniulus m l>:iiidï. or Aiit--

r.vjcl)n¡! th( s

l;!njmulus ci<.ii

ty:thi'

!s nvfir

,-h..l»-.

IK'^

FAMILY

c

LOW CLOUDS

Surface to 6500 feet

7. STRATOCUMULUS

8. STRATUS

9. CUMULUS

10. CUMULONIMBUS

L_ Layer ol

O stralocumulu;

T Stratus "^.o,

LiO frACtostiatus

but not of

' ' -ath

I, bul (i<: SirjiuN

Figure 6.1. — Characteristic cloud forms. (U.S. Department of Commerce, Weather Bureau "Cloud Forms" Revised May 1962).

36
Den»* Cirrus, i n [j-.u-h.^s 'ir

Unfits »httaves. u.4ual)v rtot

tncreawing and pnsKibly lht<

r«ni»ni{ of tht; upper iiart »f

« Cumulii-nlmlwH; orOriUH

with tfproutlflfts in thr form

of »IR:II1 turrets, ï>r Cirrus

in (Iw form ot IUÍIíí.

lui >'«-• ccl'-^'i.a à'"

pre(<cfice ot iht- haîo Inipli'

an abuiMtini;«- <>i iv« cryi^i^iiM>d thtd iritenainftMin is us> -

fu) m <lii(tin(;uikhink( cirru,-

Ctuud« frnm hitKC ilolt.

AlUttlraitis.tli« greiilui' pni-i

ot whirhiüsufitcicntly dons'-

I« hid«' the sun or imxin, ^.r

Ntmbnstraiu».

ilie form

AI«K:umulu.s. thv cruai pju-t

thr tk>ud<t t>crur Ji one ¡ir

>lii and t tK> el«menlH

ir«' contmtutiy char.siitK ''*)

ipiieurance.

"-?-*fc

OC7'

AKcicumulus tn two or nx^M'

Uyrr.s, uttu^tly itpaqut- ir,

places, iMá (kot |ir«igrc»4tvel>

inVHdlnd thu sky; or oiuctui?

luyer o( Allorumulus n<>t

prufireKsively invadinK thf

ky;i>rAlU>ciiniulus Kit^ütttcr

with Altustr^tUH or Nimbû-

]yjg Castellated

.aitocumuius '.

i

Altucuinulus with itproutinK^

m.l h« furm oí itm:ill toK-crs

or tuttlrmifnis, or Allocumulus having; the ¡it'l^araniie

of vumulifnrm lufiH.

Cumulus of niiidrrme or

Wrong v('rlic:il cxtcni, ¡(vnBTiiUy with protülieraiweit in

IheformoltlomvHor litwrrs,

either accompanied it r not

by other Cumulus or l>y

Stritto-cumulud, u)l hav initheirtxisetiat the ¡tame levii.

Low clouds

. OÍ bad

stratum iriictUK of t).i<l

wi^altMT o r CumuluK frartus

(if bad wealht-r, or txitli

(pannus), uauutiy Itelutt

AlInwIraliisEirNimtMislratUü.

Cumjionmit Ä us. rhc ^ummit^

(If which, at leant pariiJlly

lark Hharp E uilinirs, but an

nrtiher cip arlv fibroutf

(cirrtrorm' .or in the for m

1 I: Cumulu«

Strat'iouniuiu» or StratuB

may jtino be presión).

CumulUK and StraiiK-uniuluH

(Hht-r than thai lormi-d from

the «preadinft nut of Cumulua;

ilic bjse of Ihr CumuluH Is

ai a different level IriNn

that ta tke StraiocMmulu«.

,mi..iiiu»

itii- ïpnjdint, líui ui

iilLn; CumuluH nuv a I

preherit.

r accumpjiaed

V Cumuk>i)imlNi:t wi

r fibrnuii upper part,

y Cumulu», Sirai<>t:umuluí,

r piinmi«.

37
38
There are several sets of standards that may

logically be applied to fire-weather stations.

One set of standards covers the location of the

station, the measurements taken, and the instruments used from the standpoint of data

comparability. These standards apply primarily

to networks of permanent stations such as

those maintained for climatological and firedanger rating purposes. The objectives ofthese

standards are to assure that: (1) data collected

at any given time at one station are comparable

to simuar data collected at the same time at all

other stations in the network; and (2) data

collected at a particular station at any given

time are comparable to previous data collected

at the same station.

A second set, which applies to all stations,

has to do with the location and arrangement of

the station with regard to installation and exposure requirements of the instruments involved. The objective of such standards is to

insure the collection of accurate data that effectively samples the weather prevailing over

the specific station area.

The term "standard fire-weather station" as

used in this handbook refers primarily to the

permanent type of station that is part of a

weather collection system or network. Such

networks are maintained for fire-weather forecasting and to obtain fire-danger ratings. Many

of these network stations also serve as National

Weather Service climatological stations. Both

sets of standards described above apply to these

standard fire-weather stations.

There is a third set of standards that applies

to station networks. These are the administrative standards which prescribe observation

time, method of recording data, precision of

readings, etc. The items vary according to the

purpose for which the station is maintained and

are not covered in detail in this handbook.

They are, nonetheless, important considerations for data comparability. A fire-weather

observer should become thoroughly familiar

with all the administrative standards that apply

to his station.

In the following pages, guidelines for the

location and layout of the standard fire-weather station are provided, equipment needs are

listed, and installation and exposure requirements of the recommended instruments are

detailed.

A fire-weather station condition report that

summarizes the standards presented in this part

of the handbook is included in the Appendix.

599-270 O - 76 - 4

39
"M

CHAPTER 7

THE STANDARD

FIRE-WEATHER STATION

7.1 LOCATION

The standard fire-weather station should be

located in a large opening, away from obstructions and sources of dust and surface moisture.

The station should be on level ground where

there is only a low vegetative cover. Furthermore, it should be situated to receive full sun

for the greatest possible number of hours per

day during the fire season. If located on a slope,

a south or west exposure is required to meet

fire-danger rating standards (Deeming, Lancaster, Fosberg, and others 1972).

The following rules should govern the location of a standard fire-weather station:

1. Locate the station in a place that is representative of the conditions existing in the general area of concern. Consider vegetative cover

type, topographic features, elevation, climate,

local weather patterns, etc.

2. Select a site that will provide for longterm operation and a relatively unchanged exposure. Consider site development plans, e.g.,

roads, buildings, parking areas; ultimate obscuration by growth of vegetation; observer

availability; etc.

3. Arrange the station so as to give data that

are representative of the specific area in which

the station is situated. Consider exposure requirements for each instrument in relation to

such things as prevailing wind, movement of

the sun, topography and vegetative cover, nearby reflection surfaces, and wind obstructions.

In accordance with the above rules, the following situations should be avoided when selecting a station site:

1. Sources of dust such as roads and parking areas. If unavoidable, locate station at least

100 feet on the windward side of the source.

2. Sources of surface moisture such as irrigated lawns, pastures and gardens, lakes,

swamps, and rivers. If unavoidable, locate station several hundred feet to the windward side

of the source.

3. Large reflective surfaces such as white

painted buildings. If unavoidable, locate station on north side but far enough away so as

not to be artificially shaded; at least a distance

equal to the height of the reflective surface or

50 feet, whichever is greater.

4. Extensive paved or black-topped areas. If

unavoidable, locate station at least 50 feet to

windward.

5. Large buildings, trees, and dense vegetation. Locate station at least a distance equal to

the height of the obstruction.

6. Distinct changes in topography such as

hummocks, gullies, peaks, ridges, steep slopes,

and narrow valleys.

7.2 EQUIPMENT LIST

The standard fire-weather station should

contain the following equipment:

1. Cotton region instrument shelter including the support.

2. Standard maximum-minimum thermometers including a Townsend Support.

3. Electric fan psychrometer.

4. Contacting anemometer equipped with

1/60-mile contacts and pole mount.

40
5. Mechanical wind counter equipped with

a timer.

6. Standard 8-inch rain gage including the

support.

7. Wind direction system — including the

vane and remote readout.

Highly desirable, especially for fire management and climatological purposes, are:

1. Hygrothermograph.

2. Recording rain gage.

In addition to the above, these items may be

required for fire-danger rating purposes:

1. Fuel moisture sticks or other fuel moisture analog.

2. Fuel moisture scale or other analog readout device mounted in protective shelter.

7.3 LAYOUT

Arrangement of Equipment

A recommended ground plan for a standard

fire-weather station is shown in figure 7.1. This

particular arrangement of equipment affords a

free flow of air and full exposure to available

sunlight. Station size should be based on the

individual situation. Ideally, the size should be

large enough to accommodate additional instruments as they become necessary. An area 15

feet by 15 feet should, however, be considered

a minimum size for proper exposure of minimum instrumentation.

Grounds

The station grounds should be free of tall

vegetation. Brush and trees should also be kept

down within a 20-foot radius of the station. A

native perennial grass ground cover is ideal provided it is kept well clipped (about 4 inches)

and is not watered. Graveled paths to the various instrument locations are desirable since

they will not become dusty during dry weather

or muddy during rainy weather.

Fence

A fence around the station site is not essential unless there is danger of instruments being

upset or otherwise damaged by animals or curious people. However, a fence often improves

the appearance of the station and tends to discourage tampering by unauthorized personnel.

If a fence is installed, it should be no more

that 4 feet high and constructed of open type

material such as woven wire. A picket fence, for

example, is unacceptable since it would restrict

the free flow of air across the enclosure.

Suggested Layout For A Standard FIRE-WEATHER STATION

A. Standard rain gage

B. Recording rain gage

C. Anemometer pole

D. Accessory shelter

E. Instrument shelter

F. Duff bed

G. Scale shelter

Figure 7.1. — Ground plan for a standard fire-weather station.

41
CHAPTER 8

INSTALLATION

AND EXPOSURE

OF INSTRUMENTS

8.1 INSTRUMENT SHELTER

A properly installed instrument shelter will

meet the following requirements:

1. Open to the free movement of air.

2. Positioned over a low vegetative cover. ^

3. North-facing door.

4. Shelter floor 4 feet above ground.

5. Shelter floor level and plumb.

6. Shelter firmly secured to stand.

7. Stand firmly secured to ground.

At a permanent fire-weather station, it is advisable to fasten the legs of the shelter stand to

concrete footings or to metal or treated wood

stakes. Burying the legs of the stand is not recommended for several reasons: the buried portion of wooden stands will rot, and burying the

legs of a 4-foot-high stand will resultin the shelterfloor being less than 4 feet above the ground.

Metalmountingpins of the type shown in figure

8.1 can aid proper instrument shelter installation in many situations. These pins are easy to

install and can aid in obtaining a level mounting

for the shelter (fig. 8.2).

Remember, the instrument shelter is a

screen for temperature-sensitive instruments. It

is not a storeroom, or even a place for other

instruments (fig. 8.3).

Figure 8.1.— Instrument shelter mounting pin. (See

Appendix for detail drawings.)

If vegetation is absent and cannot be established,

use a 2-inch bed of forest litter or small, washed,

gravel.

42
Figure 8.2. — Installing and levelir^ instrument shelter using mounting pins.

43
8.2 STANDARD MAXIMUMMINIMUM THERMOMETER

The standard míiximum-minimum thermometer equipped with a Townsend Supportis

designed to be exposed in an instrument shelter.

Townsend Support

Fasten the Townsend Support at the center

of the instrument shelter cross board. Make

sure the Support is properly oriented so that

the spinning clamp is on the bottom (fig. 8.3).

Maximum Thermometer

Mount the maximum thermometer in the

spinning (lower) clamp of the Townsend Support about two-thirds of the way up the stem

from the bulb (near the 80° mark on a- 20° to

120° F. scale thermometer). If mounted too

near the middle, the mercury column might

separate when whirled and part of it may become lodged at the top of the stem.

Tighten the thumbscrew on the clamp

securely to prevent the thermometer from

being thrown out when whirled. When properly

Figure 8.3. — Suggested arrangement of instruments

in a cotton region siielter. Notice that only

temperature-sensitive instruments are installed in

this shelter.

mounted, the bulb end of the maximum thermometer is on the left and raised about 5°

above the horizontal. This position facilitates

the flow of mercury as temperature rises and

minimizes the chance of mercury retreating

through the constriction as temperature drops.

Minimum Thermometer

Mount the minimum thermometer in the

upper clamp, just slightly beyond the middle of

the stem (near the 40° mark on a —60° to 100°

F. scale thermometer).

Tighten the thumbscrew on the clamp to

hold the thermometer in place. When properly

mounted, the bulb end of the minimum thermometer is on the left and roughly 5° below

the horizontal. This position facilitates the

downward movement of the index when temperature drops and minimizes the chance of the

index rising as temperature rises. It also tends

to prevent accumulation of vaporized liquid

above the column orresulting bubble formation.

CROSS REFERENCE: Description 1.1;

Operation 10.1 ¡Maintenance 16.

8.3 ELECTRIC FAN

PSYCHROMETER

Locate the psychrometer in the right front

portion of the instrument shelter and fasten to

the floor board (fig. 8.3). Make sure that the

installation of the psychrometer does notinterfere with the whirling of the maximum thermometer. Observe the polarity of the battery

wires when connecting the fan to the battery.

Insufficient ventilation of the wet bulb will

occur if wires are switched.

CROSS REFERENCE: Description 2.2;

Operation 11.1-11.2; Maintenance 17.1-17.4.

8.4 HYGROTHERMOGRAPH

Set the hygrothermograph in the left front

portion of the instrument shelter (fig. 8.3).

Make sure it is placed far enough forward so it

does not interfere with the whirling of the

maximum thermometer.

CROSS REFERENCE: Description 2.3;

Operation 12; Maintenance 18.

44
Figure 8.4. — A standard anemometer installation 20 feet above open, level ground.

8.5 ANEMOMETER

The anemometer should be exposed 20 feet

above open, level ground (fig. 8.4). This standard height must be adjusted to compensate for

height of ground cover, uneven ground, and

nearby obstructions. The anemometer does not

need to be at the weather station enclosure. It

can be one-fourth mile or more avsray if necessary to sample adequate air movement representative of the geographic area of concern.

Height Adjustment

Uneven Ground

In rolling country or rough ground characterized by depressions and ridges, mount the

anemometer 20 feet over a representative high

spot. If mounted over a low spot, increase the

height by the average depth of the depression in

relation to the surrounding high ground.

Ground Cover

Adjustment of anemometer height will depend on the density and height of the ground

cover. If the ground is densely covered with

rocks, brush, or small trees, increase the height

of the anemometer by the average height of the

ground cover.

If the ground cover is scattered, increase the

height of the anemometer by one-half the

average height of the ground cover.

If the ground cover is sparse, increase the

height of the anemometer by one-third the

height of the ground cover.

Nearby Obstacles

No adjustment of anemometer height is necessary if an obstacle is more than seven times

its own height away from the anemometer.

If the distance between the anemometer

and an obstacle is less than seven times the

45
Figure 8.5. — In these installations the anemometer height is adjusted upwards because of nearby trees.

height of the obstacle (fig. 8.5), table 8.1 can be

used to determine the adjusted anemometer

height (USDA Forest Service 1964b).

Installation

Although mounting the anemometer on a

wood pole is the most common type of installation of fire-weather stations, iron pipe poles are

much in evidence (figs. 3.1, 8.4, 8.5, 8.6, and

8.7).

Metal towers (fig. 8.5) are being used more

often, especially where anemometer heights

in excess of 25-30 feet are required and where

portability is a major consideration in establishing temporary field stations. Metal towers

are available in a variety of forms: (1) onepiece towers of a specified height; (2) stacked

10-foot sections that are extended and bolted

together; (3) telescoping sections that crank

up and down; and (4) foldover models equipped with a winch-hand crank for raising and

lowering the upper half of the tower.

Regardless of the type used, the installations

should accomplish the following: (1) be windfirm; (2) allow easy access to the anemometer;

(3) accommodate attachment of the readout

device; (4) provide for periodic adjustment of

anemometer height; and (5) be compatible

with any existing lightning protection system.

These rules apply to temporary field installations (fig. 8.7) as well as to permanent fireweather station installations.

Lightning Protection

In many areas, good safety practice requires

adequate lightning protection on the anemometer as well as on the wires leading to the readout device that is located inside a lookout

tower or nearby building.

Lookout Tower Installation

If the anemometer is mounted on a lookout

tower (fig. 8.8) follow these procedures:

46
Table 8.1. —Anemometer height (20-foot standard)^ correction table

Distance to Height of obstacle

obstacle 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Feet — — 'Feet

10 27 — — — — — — — — — — — — — —

20 25 34 — — — — — — ~ — - ~ - ~ -

30 24 32 41 — — - — — ~ -- - - ~ - -

40 22 30 39 48 ~ ~ ~ - - - ~ ~ ~ - ~

50 21 29 37 46 55 -- -- -- -- -- -- - -- -- --

60 21 27 35 44 53 62 — — — — — — — - —

70 20 26 34 42 51 60 69 - - " - ~ - - --

80 20 24 32 40 49 58 67 76 ~ — - - - - --

90 20 23 31 38 47 56 65 74 83 - - - - - ~

100 20 22 29 37 45 54 63 72 81 90 -- -- -- -- --

120 20 21 26 34 42 50 59 68 77 86 95 104 — — —

140 20 20 24 31 39 47 55 64 73 82 92 100 109 118 —

160 20 20 23 28 36 44 52 60 69 78 87 96 105 114 123

180 20 20 22 26 33 41 49 57 65 74 83 92 101 110 119

200 20 20 20 24 30 38 46 54 62 70 79 88 97 106 115

220 20 20 20 23 28 35 43 51 59 67 75 84 93 103 112

240 20 20 20 22 26 32 40 48 56 64 72 80 89 98 107

260 20 20 20 21 25 30 37 45 53 61 69 77 85 94 103

280 20 20 20 20 24 28 34 42 50 58 66 74 82 90 99

300 20 20 20 20 23 26 32 39 47 55 63 71 79 87 95

350 20 20 20 20 20 23 27 33 39 48 55 64 71 80 88

400 20 20 20 20 20 21 25 28 34 40 48 56 64 72 80

450 20 20 20 20 20 20 22 26 29 35 41 48 56 65 73

500 20 20 20 20 20 20 20 23 27 30 36 42 49 56 65

600 20 20 20 20 20 20 20 20 21 25 28 32 38 44 50

700 20 20 20 20 20 20 20 20 20 20 23 27 31 34 40

800 20 20 20 20 20 20 20 20 20 20 20 22 26 29 33

900 20 20 20 20 20 20 20 20 20 20 20 20 20 24 28

1,000 20 20 20 20 20 20 20 20 20 20 20 20 20 20 22

1,100 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20

^ The computed anemometer heights do notinclude an adjustment for uneven ground or ground cover These

adjustments must be added to table values.

^For distances less than height of obstruction, place anemometer 20 feet above the obstruction.

1. Clamp a piece of #2 copper conductor

onto the anemometer pole (if pipe) or the anemometer itself (if pole is wood).

2. Run the conductor underneath the catwalk of the lookout tower cab and clamp it to

the existing lightning protection system.

3. Install a carbon block lightning arrester

(#402-RR, or equivalent) on the tower leg. The

wire connecting the anemometer to the readout device must first go through this arrester;

then the wire can be run into the tower cab.

Furthermore, this wire must be solidly connected to both the anemometer pole and the

tower.

47
Figure 8.6. — This anemometer installation allows easy access to the anemometer and provides for periodic

height adjustment. The wire on the right of the pole connects the anemometer to a wind counter located in

the fire dispatcher's office.

'- -~". '"-^¥"'i¿---^?*~*^v'^^a•v1ä'^

F^ure 8.7. —This temporary anemometer installation was established to monitor weather for prescribed

burning operations.

48
LOOKOUT LIGHTNING PROTECTION

CLAMP^

NO. 2

CONDUCTOR-

"U" CLAMP^

NO. 402-RR

CARBON BLOCK

TNING ARRESTER

, WIND COUNTER

TOWERMOUNTED

ANEMOMETER

TOWER GROUND CONDUCTORAS^

POLE-MOUNTED

ANEMOMETER

NO. 402-RR

CARBON BLOCK

LIGHTNING ARRESTER

WIND

COUNTER

CLAMP

NO. 2

CONDUCTOR

TOWER GROUND CONDUCTOR

Figure 8.8. — Suggested method for obtaining adequate lightning protection at lookout anemometer installations: Left, Anemometer pole on tower; right, anemometer pole on ground.

Ground Installation

The following procedures apply if the anemometer is mounted on a pole in the ground,

either at a lookout station (fig. 8.8) or at a

valley bottom station (fig. 8.9):

1. Clamp a piece of #2 copper conductor

onto the pole (if pipe) or the anemometer itself

(if pole is wood).

2. If a ground wire from an existing lightning protection system is available nearby, run

the conductor down the pole and clamp onto

this ground wire.

3. If an existing ground wire is not available, install a ground rod near the pole and run

the conductor down to it.

4. Install a carbon block lightning arrester

(#402-RR or equivalent) on the tower leg or

exterior of the building where the readout device is located. Before the wire connecting the

anemometer to the readout device enters the

building, it must pass through this arrester. Be

VALLEY STATION LIGHTNING PROTECTION

NO 2

CONDUCTOR

GROUND ROD

NO 402-RR CARBON BLOCK

LIGHTNING ARRESTER

Figure 8.9. — Suggested method for obtaining adequate lightning protection at valley bottom anemometer installations.

49
certain that the wire is solidly connected to

both the anemometer pole and the tower or

building it is entering.

CROSS REFERENCE: Description 3.1;

Operation 13; Maintenance 19.

8.6 WIND COUNTER

Location

The location of the wind counter is largely a

matter of observer convenience. If periodic

windspeed observations are required throughout the day, or if the observation interval is

relatively long, an office installation may be

desirable (fig. 8.10). When making office installations, be certain that appropriate lightning

protection regulations are observed.

If the wind counter is located atthe weather

station, its installation must not interfere with

exposure requirements of other instruments.

The instrument shelter is for temperaturesensitive instruments and is not an acceptable

location for a wind counter. A small weatherproof cabinet, located about 41/2 feet above the

ground on or near the anemometer pole, makes

a handy wind counter installation (fig. 8.11).

Plans for constructing the cabinet shown in figure 8.11 are provided in the Appendix.

F^ure 8.10. —The wind counter and wind direction

indicator are often installed in the fire dispatcher's

office.

Figure 8.11. — A small accessory cabinet for installation of wind counter and wind direction readout

device. The upper part of the cabinet can be used

for tools and supplies.

50
Installation

Weatherproof insulated copper lead-in wire

should be used to connect the wind counter to

the anemometer. When connecting the battery

to the counter, be sure to observe polarity of

the battery wires.

An important consideration when installing

a wind counter is the relationship between

length and diameter of wire, electrical resistance, and battery voltage. As the line distance

between anemometer and wind counter increases, the resistance increases; thus, you may

need additional voltage when very long line distances are involved. The diameter of the wire

can modify the above relationship since resistance decreases as the diameter of the wire increases. A final and potentially complicating

factor is that too much voltage can burn the

anemometer contacts.

The 10-minute wind counter, as a case in

point, can be remotely located for as much

as a mile without increased voltage providing a #20 or #22 copperweld twin-conductor

wire is used for connecting the anemometer to

the battery (USDA Forest Service 1969).

Because of the above factors, it is recommended that an electronic technician check the

proposed design before installation and

operation.

CROSS

Operation

19.12.20.

REFERENCE: Description 3.1;

13.1, 13.2; Maintenance 19.11,

8.7 WIND VANE

Location

A wind vane equipped with an attached

readout device is recommended for use at the

standard fire-weather station. The vane can be

mounted on the same pole as the anemometer

(figs 3.1 and 8.4).

The wind direction readout device can be

located either in the office (fig. 8.10) or at the

weather station, depending on observer convenience. If located in an office, proper lightning protection practices should be observed.

If located at the weather station, the readout

device can be installed in the same cabinet as

the wind counter (fig. 8.11).

I f\fF'-ji!

Figure 8.12.—Wind direction indicator. L^hted

lamps indicate wind direction.

Installation

The two most important items when installing a wind direction system are:

1. Proper orientation of the wind vane in

relation to true north.

2. Careful wiring of the readout device to

the wind vane so that the direction indicated on

the readout device corresponds to the direction

indicated by the vane.

Use insulated, weatherproof cable to connect wind vane to readout device. A 10-lead

cable is required for the wind direction indicator in figure 8.12.

True North Orientation

The following procedure is useful for obtaining proper orientation of both the Stewart

and other makes of wind vanes:

1. Remove the front cover from the wind

vane housing.

2. Rotate the wind vane arrow until the

north contact is closed, causing the "north"

indicator lamp to light.

51
3. Scribe a line on top of the wind vane

housing directly under and parallel with the

shaft of the arrow.

4. Replace front cover and extend the

scribe line down the face of the housing.

5. Paint scribe mark, or install a strip of

plastic tape, so it is visible from the ground

when the wind vane is on the pole (fig. 8.13).

6. Drive a stake so that it is directly under

the center of the wind vane housing, when the

wind vane is in operating position. Use a compass and sight a line from this stake (point A)

to true north.

7. Drive a second stake (point B) about

100 feet from point A along the sighted line

to true north.

8. While the wind vane is in operating position, backsight a line from point B to the

painted scribe line on the wind vane.

9. Adjust position of the wind vane until

the line sighted from point B to the wind vane

is exactly south (180°).

CROSS REFERENCE: Description 3.2;

Maintenance 21.

8.8 STANDARD 8-INCH RAIN GAGE

Stands or mounts for both the large and

small capacity 8-inch rain gage are shown in

figures 4.2, 4.3, 8.4, and 8.14. The installation should be level, plumb, and firmly fixed

in the ground (fig. 8.14). The top of the gage

should be 36 inches above the ground.

When properly installed and located, the

rain gage will be far enough away from high

obstacles so that a 45° angle from the top of

the gage will clear any such obstacle (fig. 8.4).

CROSS REFERENCE: Description 4.1;

Operation 14.1; Maintenance 22.1.

8.9 RECORDING RAIN GAGE

The factors governing standard rain gage

exposure apply equally to the location of recording rain gages. Mount the instrument at

ground level on a heavy wooden or concrete

base. The installation must be level, plumb,

and windfirm.

.J" •-

Figure 8.13. — Wind vane with scribe mark to assist in

true north orientation.

F^ure 8.14.— The rain gage installation should be

level and plumb.

52
Figure 8.15. — Recording rain gage mounted on tower for snow measurement.

If the gage will be used to measure snow,

install it on a platform or tower (fig. 8.15).

The height will depend on the expected depth

of accumulated snow. If the gage is left on

a tower or platform year-round, it should

not be used to obtain precipitation data

during snow-free periods. Rather a standard

gage installed with its top 3 feet above the

ground should be used. This is necessary to insure data comparability with other locations.

The recording rain gage record can be used to

obtain time and duration of precipitation regardless of method of installation or time of

year.

CROSS REFERENCE: Description 4.1;

Operation 13.4; Maintenance 22.2-22.3.

8.10 FUEL MOISTURE STICKS

Duff Bed

Prepare a bed of coniferous needles or

hardwood leaves 2 inches deep over a 3-footsquare area. The ground surface beneath the

duff bed usually requires treatment of some

sort to eliminate herbaceous vegetation. Place

the needles on the surface of the ground (not

in a pit) to assure normal runoff of water after a rain. The purpose of the duff bed is to

provide a standard reflection surface and to

prevent hard rains from splashing mud on the

sticks. A burlap sack fastened to the ground

under the sticks would be a good substitute if

litter were not readily available.

Stick Exposure

Weathering, i.e., the effects of sun, rain,

wind, and repeated wetting and drying, reduces the ovendry weight of fuel moisture

sticks over time. For this reason, install a new

set of indicator sticks at the beginning of each

season and, if necessary, periodically throughout the season. Install the sticks several days

prior to the date measurements are to start so

they have sufficient time to attain equilibrium

with the surrounding air. Expose the sticks in

a horizontal position 10 inches above a fresh

bed of dry needles or leaves. Place two galvanized wire racks 16 inches apart over the

duff bed to support the sticks (fig. 8.16).

Screening

In the past, at many fire-weather stations

of the open type, fuel moisture sticks have

been shaded in an attempt to simulate the effect of a forest canopy on the moisture content of fuels on the forest floor. This shading

is accomplished by use of screens.

In the Western States, a double layer of

14-mesh wire screen held taut in a 3-footsquare frame 13 inches above the ground has

been used to produce a degree of shade about

equal to that existing on an old-growth area

from which three-fourths of the canopy has

been removed (fig. 8.17). This practice, however, has generally been discontinued at fireweather stations.

Whether or not screening is used depends

on the objective of the fuel stick measurements. If the measurements are being taken to

make decisions on when to broadcast burn a

clearcut unit, for example, screening should

not be used since there would be no tree canopy over the fuel complex being appraised.

Current fire-danger rating procedures do not

use screens.

CROSS REFERENCE: Description

5.1,5.2; Operation 15; Maintenance 23.

53
Figure 8.16. — Fuel moisture stick installation over a bed of coniferous needles.

Figure 8.17. — Screen

installed over fuel stick

at valley station to simulate

shade of forest canopy.

54
8.11 FUEL MOISTURE SCALE

An Appalachian scale mounted in an Appalachian scale shelter is recommended for

weighing fuel moisture sticks at standard fireweather stations (figs. 5.2 and 8.4). Construction plans for the Appalachian shelter are in

the Appendix.

The scale shelter should be plumb and

firmly secured to the ground. Its location

should be such that it neither shades the fuel

sticks nor interferes with the exposure of the

instrument shelter or rain gage.

Install the scale on the mounting board, or

backplate, of the shelter and level it as shown

in figure 8.18. The scale must be exactly

square and plumb to yield accurate readings.

Once the scale is properly mounted in the

shelter, easy zero adjustment can be obtained

by manipulating the three wing nuts located

around the face of the scale.

CROSS REFERENCE: Description 5.3;

Operation 15; Maintenance 24.

Figure 8.18. — Appalachian scale installed in an Appalachian shelter. Both the shelter and the scale

should be level and plumb.

55

599-270 O - 76 •
CHAPTER 9

PORTABLE, AUTOMATIC

AND REMOTE

WEATHER STATIONS

A detailed treatment of portable, automatic, and remote weather stations is beyond the

scope of this handbook. The fire manager

should be aware of their existence and their

potential application for fire-weather purposes. For these reasons, a brief discussion of

each follows. Further information can be obtained from the references provided.

9.1 PORTABLE WEATHER

STATIONS

A portable weather station is one designed

and packaged for easy transport, installation,

and operation. A variety of such stations has

been developed for recording data at wildfires, prescribed fires, and research field locations. They are also useful for checking out

potential sites for permanent fire-weather

stations.

The simplest, least expensive, and most

popular portable unit is the belt weather kit

(fig. 9.1). It is merely a collection of individually available instruments placed together in a

common carrying case. The description, operating instructions, and maintenance requirements for belt weather kit components are included in the appropriate parts of this handbook.

Other portable units vary greatly in design,

type of sensors used, accuracy of measurement, and overall reliability of operation.

They range from the fairly simple, "homemade" units (USDA Forest Service 1964c) to

fairly sophisticated commercial units.

The important point for observers to recognize is that the same fire-weather measurement principles that apply to permanent stations are equally applicable to portable stations. Observers should know how the instruments or sensors work, their accuracy and reliability, exposure requirements, and maintenance needs.

9.2 AUTOMATIC WEATHER

STATIONS

Automatic weather stations are those having the capability to collect and display data

without constant attention of an observer.

Collected data are usually displayed on a dial

or recorded continuously on a chart or tape.

Some automatic stations developed for fireweather purposes are also portable (Murray

56
and Countryman 1968). A number of highly

sophisticated automatic weather stations are

commercially available from major instrument

companies, many of which are somewhat

portable.

9.3 REMOTE WEATHER STATIONS

A remote weather station is one that collects data at one location and transmits it for

readout at another location. Stations of this

type are usually expensive and have a fairly

high maintenance cost. A number have been

incorporated into fire-weather collection networks throughout the country (Lewis 1966;

Hauck and Taylor 1968).

The majority of remote stations transmit

data via radio although transmission by land

line is also feasible, especially where short distances are involved (Breuer 1968).

Figure 9.1. — Belt weather kit, open and closed view.

57
58
ART 3,

OPERATING INSTRUC

Fire-weather stations are normally

equipped with relatively simple instruments

that are, for the most part, quite easy to operate. This is, in one sense, unfortunate because it

leads many observers to feel that it is unnecessary to learn how to operate their instruments

before attempting to obtain data from them.

Furthermore, fire managers rarely see any

need to provide training in instrument operation for their fire-weather observers. The net

result of this casual attitude toward fireweather observation is the perpetuation of improper measurement techniques and the routine collection of useless weather data.

Proper measurement techniques are governed to a large extent by the operating principles and the exposure requirements of the

instruments involved. This is why these items

are discussed at length in parts 1 and 2 of this

handbook. An observer who understands instrument operating principles and exposure

requirements will immediately see the logic in

the operating instructions that follow.

59
CHAPTER 10

THERMOMETERS

10.1 READING THERMOMETERS

Observe the following precautions when

reading any liquid-in-glass thermometer:

1. Do not touch the glass or hold hands

near the bulb.

2. Do not breathe directly on the thermometer. Keep face back except when making final reading.

3. If instrument is hand-held, stand in

shade or hold thermometer in shade of your

body. Wherever possible, face into the wind.

4. Avoid parallax error when reading thermometers. Notice in figure 10.1 that a

straight line from the observer's eye to the

meniscus or the index forms a right angle with

the thermometer stem.

READING THERMOMETERS

A B

-II>

Mercury

Thermometer

READ

ÏÏERË ' -E>

Alcohol

Thermometer

Figure 10.1. — Avoid parallax error when reading

thermometers.

5. Doublecheck your reading before recording.

It is easy, for example, to incorrectly read

a 55 instead of 65, or a 30 instead of a 40.

10.2 MAXIMUM-MINIMUM

THERMOMETERS

Maximum and minimum temperatures,

usually taken in the afternoon for fire rating

purposes, normally refer to the 24-hour period between basic observation times. When

this is the case, simply read the thermometers

at observation time, record the readings, and

reset the thermometers.

When taking observations at the basic observation time, remember that the maximum

temperature read today cannot be lower than

the dry-bulb temperature yesterday or today.

Also, the minimum temperature, read today,

cannot be higher than the dry-bulb temperature yesterday or today.

Maximum and minimum temperatures taken for climatological purposes often refer to

the 24-hour period from midnight to midnight. When this is the case, follow this

schedule:

At 0800 hours. — Read minimum temperature first and record as today's minimum

temperature.

Read maximum temperature. If this maximum is higher than the maximum temperature recorded at yesterday's basic observation time, it means that temperature continued to rise yesterday after the reading

was taken. Correct yesterday's entry accordingly.

Reset both thermometers ~ maximum

thermometer first, minimum last.

60
A t basic observation time. — Read both

thermometers. If minimum temperature is

lower than today's 0800-hour reading, correct the minimum temperature entry on

the observation record.

Read and record today's maximum temperature.

Reset both thermometers — maximum

thermometer first, minimum last.

10.3 STANDARD MAXIMUMMINIMUM THERMOMETERS

See figure 10.2 and procedure below for

the correct reading and setting of standard

Figure 10.2. — Reading and setting maximum-minimum thermometers.

61
maximum-minimum thermometers in a Townsend Support. Caution: Always read the minimum thermometer first and reset it last because the index rod can easily j^gle and slide

away from its correct position.

(1) Read minimum thermometer first.

a. Read minimum temperature from

the right or upper end of the index.

b. Read current temperature from top

of alcohol column.

c. Do not reset at this time.

(2) Read maximum thermometer.

a. Unlock and slowly lower maximum

thermometer to a vertical position

so that the mercury column is resting

on the constriction in the tube.

b. Read maximum temperature from

the top of the mercury column.

(3) Set maximum thermometer first.

a. Whirl until its reading agrees (within

1°) with reading at top of alcohol

column of minimum thermometer

(or dry bulb).

b. Lock maximum thermometer to

nearly horizontal position.

(4) Set minimum thermometer last.

a. Invert until index drops to end of

alcohol column.

b. Return to its nearly horizontal

position.

CROSS REFERENCE: Description 1.1; Installation and Exposure 8.2; Maintenance

16.1-16.4.

10.4 SIX'S COMBINED MAXIMUMMINIMUM THERMOMETER

1. Read maximum and minimum temperatures at lower end of index (fig. 10.3).

a. Read maximum temperature on right

scale.

b. Read minimum temperature on left

scale.

2. Reset by using a magnet to draw each

index rod down to the top of its mercury column (fig. 10.3).

CROSS REFERENCE: Description 1.1;

Maintenance 16.1-16.3, 16.5.

Figure 10.3. — Reading and setting Six's maximum-minimum thermometer.

62
CHAPTER 11

PSYCHROMETERS

Poor psychrometer operation is one of the

most common observational errors at fireweather stations. To obtain accurate results

with the psychrometer, the observer must follow certain basic instructions, listed below, in

addition to the specific operating instructions

listed on the following pages.

11.1 GENERAL OPERATING

INSTRUCTIONS

1. The two thermometers should agree

within a half graduation when both are read

as dry bulbs (wicking completely dry). Thermometers having 1° graduations should agree

within 1/2° ; those having 2° graduations within 1° ; etc.

2. Wet-bulb wicking must be clean and

snug fitting. Wicking should extend about 1

inch up the stem, above the bulb, to minimize

error from heat transfer along the stem; and it

should extend 1 inch below the tip of the

bulb to serve as a water reservoir (fig. 11.1).

Change wickir^ whenever it gets dirty, but at

least every 2 weeks (see section 17.1).

3. Make observations in an area exposed

to free air but protected from sunlight, radiated heat, and precipitation.

4. Wet the wet-bulb wick thoroughly just

prior to ventilation (fig. 11.2). Do not get

water on the dry bulb or it will tend to act as

a wet bulb. Use only distilled water, clean

rainwater, or other clean, mineral-free water

of about air temperature. Unless the water

container is capped, the water will be cooler

than free air.

I

Figure 11.1. — A properly installed wick on wet- and

dry-bulb psychrometer.

63
Figure 11.2. — Thoroughly wet the wick of electric

fan psychrometer prior to taking measurements.

Figure 11.3. — Do not wet the wick during ventilation of the thermometers.

5. Do not allow the wick to extend into

the water container either during operation or

while the psychrometer is not in use (fig.

11.3).

6. Except in cases of extremely low humidities, do not wet the wick between readings during a given observation. In order to

prevent premature drying in low humidity situations, wet the wick thoroughly, allow it to

cool naturally until mercury column completes its initial drop, then force ventilate as

needed.

7. At each observation, continue ventilation long enough to assure the wet-bulb mercury column drops to its lowest reading. This

may take from 2 to 3 minutes but can vary

considerably for a given observation.

To insure that the lowest wet-bulb reading

is obtained, continue ventilation until the

wet-bulb reading levels off or starts its return

to a higher level.

8. Record the dry-bulb temperature that

occurs in conjunction with the lowest wetbulb reading.

9. If the wet-bulb mercury column starts

to rise without a corresponding rise in the dry

bulb, this may indicate that the wick has

dried out before the lowest wet-bulb temperature was reached. In this case, wet the wick

again, allow it to precool from natural ventilation, then start forced ventilation. Repeat

procedure for reading wet and dry bulbs.

10. Do not allow body heat or breath to

influence thermometer readings. Avoid touching and breathing on thermometers when taking final readings. Face wind when making observations outside an instrument shelter.

11. Refer to Relative Humidity and Dewpoint tables provided in back of this book

to obtain relative humidity and dewpoint values from wet- and dry-bulb readings (see section 2.1). Caution: Relative Humidity and

Dewpoint tables and slide rules provided with

many psychrometers are for use at sea level

only.

12. For fire-weather purposes, the thermometer readings are usually recorded to the

nearest degree. Half degree readings are recorded to the next higher degree. Increased

accuracy, if required, can be obtained by recording to the nearest half degree and interpolating in the psychrometric tables.

13. During freezing weather, the water in

the wick must be completely frozen before attemptirig a reading. Remove all old ice by dipping in warm water prior to observation.

If wick is dry, wet it about 15 minutes before observation to allow a thin coat of ice to

64
form. Ventilation will speed up this process as

will touching the wet bulb with a piece of

clean ice or cold metal.

Ventilate thermometers until wet-bulb

temperature drops to a steady point below

32° F.; read first the wet bulb and then the

dry bulb.

11.2 ELECTRIC FAN

PSYCHROMETER

The electric fan psychrometer is designed

for operation in an instrument shelter. Refer

to section 11.1 for general instructions.

1. Check the wick.—It must be clean,

snug, and of the proper length (fig. 11.1).

2. Wet the wick. — Saturate with clean,

mineral-free water of about air temperature

just prior to an observation. After wetting, replace cover and set water container aside (fig.

11.2).

3. Ventilate the thermometers. — Air must

flow at a minimum rate of 15 feet per second.

Replace batteries at the first sign of weakness.

Be sure the motor wires are properly attached

to the battery. If they are not, the fan will

turn backwards and insufficient ventilation

will result (fig. 11.3).

4. Read the wet bulb.—Read the wet

bulb first. Watch the top of the mercury column as it retreats down the stem. It will drop

slowly and then come to rest for several seconds, sometimes longer. Take a reading at this

point. Continue to watch the column as it will

either start to return up the stem or drop still

farther down the stem.

If the wet bulb remains steady or starts to

rise (and the wick is still moist) you have already noted the lowest wet-bulb temperature.

If the column drops farther down the stem,

repeat the process of reading and watching

until you have noted the lowest point reached

by the top of the mercury column before it

starts its rise back up the stem.

5. Read the dry bulb. —Take a dry-bulb

reading immediately after each wet-bulb reading. The correct dry-bulb reading will be the

one occurring with the lowest wet-bulb

reading.

CROSS REFERENCE: Description 2.2; Installation and Exposure 8.3; Maintenance

17.1.-17.4.

11.3 PORTABLE ELECTRIC

FAN PSYCHROMETER

Operate in an open but shaded area for

best results. Avoid heat sources. Point air duct

openings away from body during operation. If

possible, place instrument on a flat surface

facing into the wind with thermometers facing upward for easier readings. Refer to section 11.1 for general operating instructions.

Specific operating instructions are as follows:

1. Check the wick.—It must be clean,

snug, and of the proper length (fig. 11.1).

2. Check the thermometers. — Inspect to

see if mercury column has separated during

transit. Allow thermometers to stabilize with

temperature of air at observation site.

3. Wet the wick. —Remove air duct and

point thermometer bulbs downward.

Thoroughly wet wick with water of about air

temperature, but do not oversaturate. Avoid

getting water into the fan compartment. Replace air duct (fig. 11.4).

HHBWÊBKÊÊÎ^^,!.^^^*

^^^^^^^^^^^^H '

MSêJ^^

Figure 11.4. — Carefully wet wick. Avoid getting

water on dry bulb.

65
4. Ventilate the thermometers. — Be sure

air duct fits snugly against thermometer

housing to avoid air leakage. Turn fan on. If

fan blows air out of duct instead of sucking

in, check battery installation. If motor slows

down or thermometer light dims, replace batteries.

5. Read the wet bulb. — Read the wet

bulb first. Watch the top of the mercury column as it retreats down the stem (fig. 11.5).

It will drop slowly and then come to rest for

several seconds, sometimes longer. Take a

reading at this point. Continue to watch the

column as it will either start to return up the

stem or drop still farther down the stem.

If the wet bulb remains steady or starts to

rise (and the wick is still moist) you have already noted the lowest wet-bulb temperature.

If the column drops farther down the stem,

repeat the process of reading and watching

until you have noted the lowest point reached

by the top of the mercury column before it

starts its rise back up the stem.

6. Read the dry bulb. —Take a dry-bulb

reading immediately after each wet-bulb reading. The correct dry-bulb reading will be the

one taken immediately after the lowest wetbulb reading has been obtained.

CROSS REFERENCE: Description 2.2;

Maintenance 17.1-17.3, 17.6.

11.4 HAND FAN PSYCHROMETER

The hand fan psychrometer is designed for

use in an instrument shelter. Except for ventilation requirements, specific operating instructions are identical to those for the electric fan

psychrometer. The observer should also refer

to general operating instructions in section

11.1. Ventilation is accomplished by hand

cranking the fan. Rapid cranking must continue without interruption until the lowest wetbulb reading is obtained (fig. 11.6).

CROSS REFERENCE: Description 2.2; Installation and Exposure 8.3; Maintenance

17.1-17.3,17.5.

11.5 SUNG PSYCHROMETERS

In order to obtain reasonably good accuracy

with sling psychrometers, stand in shaded open

area away from buildings and away from obstacles that may be struck during whirling.

If light conditions permit, face the wind to

avoid influence of body heat on thermometers.

Do not let sunlight or rain strike the thermometers. Refer to general operating instructions in

section 11.1. Specific operating instructions

follow:

1. Check the instrument. — Be sure handle

and chain are in good repair. Check thermomeHlHi k^^^J^

^^^K '^MBÉ^^P^J^A^PT

B

^^^^^^Qk<' ^ ^^

^^L^. .'^-

SH^Hj

HHEl^

Figure 11.5. — Observe top of wet-bulb column as it

retreats down the stem.

Figure 11.6. — Rapid cranking of hand fan must continue until lowest wet-bulb temperature occurs.

66
Figure 11.7. — Stand in shade. Wet the shng psychrometer wick prior to whirling.

ter column for separations. Be sure the thermometers are firmly mounted to housing.

2. Check the wick. — It must be clean, of

the proper length, and securely fastened to

bulb (fig. 11.1).

3. Wet the wick. — Saturate with a clean

mineral-free water of about air temperature

just prior to making observation (fig. 11.7).

4. Ventilate the thermometers. — Whirl at

full arm's length with arm parallel to the

ground for about 1 minute at the rate of about

200 whirls per minute (fig. 11.8).

If the humidity is very low and no shade is

available, premature drying of the wet bulb

may be a problem. This may be prevented by

Figure 11.8. — Whirl sling psychrometer at full arm's

length.

waving the psychrometer in body shade (fig.

11.9), open to breeze if possible for a few minutes before whirling in full sunshine. This will

often reduce the amount of whirling required.

5. Read the wet bulb. —Note wet-bulb

temperature. Whirl another 40 or 50 times and

read again. If wet bulb is lower than first reading, continue to whirl and read until it will not

go any lower. When lowest point is reached,

read and record (fig. 11.10).

6. Read the dry bulb. — Read dry bulb immediately after lowest wet bulb is obtained.

CROSS REFERENCE: Description 2.2;

Maintenance 17.1-17.3,17.8.

67
Figure 11.9. — Whirl psychrometer in body shade if

no other shade is available.

Figure 11.10. — Read and record lowest wet bulb obtained.

Figure 11.11. — For best results fan the hygrometer

wick before reading.

11.6 WET- AND DRY-BULB

HYGROMETER

The wet- and dry-bulb hygrometer is designed for simple operation; merely read the

thermometers whenever a relative humidity

and dewpoint determination is desired. This

procedure assumes that adequate ventilation of

the wet bulb will be accomplished naturally.

In order to achieve the maximum accuracy

possible with this instrument, fan the thermometers using a piece of cardboard for about

3 minutes before reading (fig. 11.11). Read the

thermometers to the nearest 1° F.

CROSS REFERENCE: Description 2.2.

68
11.7 THE MORTARBOARD

PSYCHROMETER

Operating instructions are as follows:

1. Check the thermometers. — Sun must

not be striking any portion of thermometers. If

shading is required, reading must be delayed

until thermometers stabilize.

2. Check the wick. — Wick must be clean

and saturated with clean, mineral-free water.

Wick may dry out under extended periods of

low humidity (below 30 percent for several

hours). To correct this situation, wet the wick

several minutes before taking a reading. If wetting is required, allow the wet bulb to stabilize

prior to reading.

3. Check the water cup. — The cap should

fit tightly on the cup and the tubing should

extend from near the bottom of the cup to 1

inch below the tip of the wet bulb. The cup

should be at least half full of clean, mineral-free

water before starting an observation.

4. Insure proper ventilation. — Insufficient

ventilation of the thermometers may occur if

winds are less than 3 miles per hour at any time

or less than 6 miles per hour during dry weather

(30-percent relative humidity or less). To insure proper ventilation, use a piece of cardboard to fan the thermometer until a minimum

wet-bulb reading is obtained. If an electric fan

has been installed, refer to section 11.2.

5. Read the wet bulb. — Eyes should be directly in line with top edge of mercury column

to avoid a false reading (fig. 11.12).

6. Read the dry bulb. — Read immediately

after wet bulb. During freezing weather, follow

general instructions given for wet- and dry-bulb

psychrometers.

CROSS REFERENCE: Description 2.2;

Maintenance 17.1-17.3,17.7.

< it

Figure 11.12. — Reading mortarboard psychrometer.

69
CHAPTER 12

HYGROTHERMOGRAPHS

Expose hygrothermographs in an instrument shelter 4 feet above the ground. For best

results, follow the operating procedure outlined below.

12.1 CHANGING THE CHART

Before installing a new chart, write the station name and number and the beginning date

in the spaces provided at the end of the chart

(fig. 2.10).

To remove the old chart:

1. Lift pens off chart using shifting lever.

2. Unlock and raise cover.

3. Lift drum from spindle being careful not

to hit pens.

4. Record "off time" on chart near last pen

mark. Record ending date on chart (fig. 2.10).

5. Pull clip and remove chart from drum.

Avoid smearing recent, wet portion of trace

with fingers.

6. Wind clock (fig. 12.1).

To install a new chart:

1. Place chart down snug against the bottom lip of the drum and wrap it tightly around

the drum.

2. Insert clip if nonslotted cylinder (fig.

12.2). If slotted cylinder, insert ends of chart

into slot on cylinder.

3. Replace drum on spindle. Position drum

so that chart time is a little faster than correct

time.

4. The pens should be refilled with ink, if

necessary (see below).

f^

Figure 12.1. — Winding clock on hygrothermograph: Left, Clock in drum type; right, clock on base type.

70
Figure 12.2. — To avoid losing part of the hygrothermograph record, install tapered charts on nonslotted cylinders.

5. Return pens to chart using shifting lever.

Check ink flow by slightly rotating drum back

and forth.

6. Turn drum to place pens at correct chart

time by rotating drum counterclockwise. This

takes up any slack in the gears.

7. Lower and latch cover.

12.2 INKING THE PENS

1. Use purple glycerine base ink made specifically for hygrothermographs (fig. 12.3).

2. Fill pen until ink first shows at each end.

If filled until ink bulges out, overinking of the

chart might result.

3. In damp weather the ink, being deliquescent, absorbs moisture so less ink should then

be used. It is especially important to keep pen

points sharp during damp weather (see section

18.2).

4. To start flow of ink, draw a piece of chart

paper through the points. This cleans out old

residue and draws a film of ink to the points.

12.3 CHECKING THE

CALIBRATION

If daily readings are taken, check calibration

at the standard observation time. If station is

not visited daily, check calibration whenever

X

K

Figure 12.3. — Inking the pens of a hygrothermograph.

71

599-270 O - 76
Figure 12.4. — Use a clean, dry, camel's hair brush to remove dirt and dust.

chart is changed. Because of the lag time of the

sensors, calibration checks should be done only

when temperature and humidity are holding

steady. Procedures are as follows:

1. Inspect instrument for obvious mechanical deficiencies.

2. Use a clean, dry, camel's hair brush to

remove dust or dirt.

3. To make a time mark, lightly deflect

each pen downward to obtain a short vertical

line on the chart. Do not deflect humidity pen

upward as this may apply excessive force on the

hairs and foul up the adjustment. Record actual

time near mark or on observation record. Compare chart time with actual time and compare

time indicated by upper pen with that of lower

pen; then, make necessary adjustment.

4. Compare maximum, minimum, and current temperatures on chart with values obtained from the maximum, minimum, and

dry-bulb thermometers (see section 11.1);

then, make necessary adjustments.

5. Compare current relative humidity on

chart with reading obtained from the psychrometer (see section 11.1). Observe relative

humidity trace for evidence of range elongation

or shortening; then, make necessary

adjustments.

CROSS REFERENCE: Description 2.3; Installation and Exposure 8.4; Maintenance 18.

72
CHAPTER 13

ANEMOMETERS

The following instructions are for anemometers exposed at the 20-foot standard height

(20 feet plus adjustment for nearby obstructions and surface irregularities, see section 8.5).

If the anemometer height is greater than the

20-foot standard height, the observed windspeed must be corrected according to special

instructions at the end ofthis section.

Windspeed refers to the average speed ofthe

wind over a period of 10 minutes. This use of a

10-minute average windspeed for fire-weather

and fire-danger observation is compatible with

recognized standards for measuring wind

(World Meteorological Organization 1969).

13.1 1/60-MILE CONTACTING

ANEMOMETER

Readout by Reset Counter

Equipped With Timer

1. Reset dial to zero,if not already done.

2. Set timer.

3. When timer stops, read dial ( fig. 13.1 ).

4. Record correct average 10-minute windspeed in miles per hour by placing decimal

point before last number on counter dial.

5. Reset dial to zero.

6. If average windspeed for other than 10

minutes is desired, simply set desired interval

on timer and divide final count by that time

interval.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5, 8.6; Maintenance

19, 20.2.

Readout by Reset Counter

1. Reset dial to zero, if not already done.

2. Using the "off-on" switch, start both the

counter and stopwatch. If using a watch with a

sweep second hand, start counter as second

hand passes 12.

3. After exactly 10 minutes, stop counter.

Figure 13.1. — Windspeed and direction can be obtained from readout devices conveniently located

on the ground.

73
4. Record correct average 10-minute windspeed in miles per hour by placing decimal

point before last number on counter dial.

5. Reset counter to zero.

6. If average windspeed for other than 10

minutes is desired, let counter run for desired

interval and divide final count by that interval.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5, 8.6; Maintenance

19,20.3,20.4.

Readout by Nonreset Counter

1. Record numbers on the counter dial.

2. Start counter and stopwatch. If using a

watch with sweep second hand, start counter as

second hand passes 12.

3. After exactly 10 minutes stop counter.

4. Record numbers on the counter dial.

5. Calculate average 10-minute windspeed

by subtracting the beginning count from the

ending count. Place a decimal point before the

last number of the result and record.

6. If average windspeed for other than 10

minutes is required, let counter run for the desired interval, subtract ending count from beRead

Here

CORRECT READING;

103.8 or 104miles

Figure 13.2. — Detailed view of anemometer dial. Dial

indicates 104 miles of accumulated air movement

past the anemometer cups.

ginning count, and divide difference by the interval used.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5, 8.6; Maintenance

19,20.

Readout by Buzzer or Flasher

1. Close switch on buzzer or flasher.

2. Immediately after the first flash or buzz,

record the time or start the stopwatch.

3. Count number of flashes or buzzes for

the desired time interval. The time interval applicable to this type of indicator is usually 4

minutes.

4. Open the switch.

5. Calculate average windspeed by dividing

the total count by the time interval.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5, 8.6; Maintenance

19,20.1.

13.2 ANEMOMETERS WITH SELFCONTAINED READOUT

Readout by Self-Contained Counter

1. Record starting count.

2. Record count at end of interval for

which average windspeed is desired.

3. Subtract beginning count from ending

count and divide difference by the time

interval.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5, 8.6; Maintenance

19.11.

Readout by Self-Contained Dial

1. Read dial at beginning of the period for

which average windspeed is desired.

a. Read the inner dial first. The index for

the inner dial is located in the outer

dial. It is a small "zero" through

which is drawn a vertical line (fig.

13.2). The inner dial is graduated in

tens and hundreds of miles.

b. Read the outer dial. The index is a

small pointer located above and just

to the left of the large dial (fig. 13.2).

When the glass cover is on the dial, the

eye has to be lowered slightly to see

this second index. The outer dial is

74
graduated in miles and tenths of a

mile,

c. The total reading is obtained by

adding the miles indicated on the

outer dial to the miles indicated on

the inner dial.

2. Read the dial atthe end of the period for

which average windspeed is desired.

3. Subtract beginning reading from ending

reading and divide the difference by the

elapsed time (minutes, hours, days, etc.).

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5, 8.6; Maintenance

19.1-19.4,19.12.

13.3 CORRECTING WINDSPEED

OBSERVATIONS TAKEN

AT HEIGHTS GREATER

THAN 20-FOOT STANDARD

An anemometer installed on top of a building or mounted on a fire lookout tower may

exceed the 20-foot standard height, even after

making adjustment for nearby obstructions.

If the total height of the anemometer is

greater than the required height (see section

8.5), the resulting windspeed observations

must be adjusted.

Table 13.1 (Cramer and Moltzau 1968) provides conversion factors to adjust windspeeds

obtained from anemometers exposed at heights

greater than 20-foot standard.

To make necessary adjustment:

1. Determine total height for a 20-foot

standard ground installation.

2. Determine total height of anemometer

(in feet) above ground.

3. Determine height of anemometer above

20-foot standard height (item 1 minus item 2).

4. Using item 3, look up conversion factor

in table 13.1.

5. Multiply observed windspeed by conversion factor. Result is 20-foot standard windspeed.

13.4 HAND-HELD WIND METER

1. Face the wind and hold the meter at

arm's length about head high; have the scale

side of meter facing you (fig. 13.3).

Figure 13.3. —Assume a face-into-wind position

when using hand-held wind meter. Keep fingers

clear of top stem when measuring winds less than

10 m.p.h.

75
2. Hold the instrument about midway from

either end being careful not to block the two

holes at the bottom or small pinhole in top

stem.

3. Observe action of the ball in relation to

left scale. If it is "bouncing" around between 2

and 9, read from the left or low scale (fig. 13.3).

If ball is rising up near 10 on left scale, cover

the top stem with your finger and read from the

right or high scale (fig. 13.4).

4. To obtain a reading, observe height attained by the ball in relation to the appropriate

scale value (see item 3 above). Usually the

height of the ball will vary considerably even

during a short period; consequently, a certain

amount of subjective averaging is often necessary to obtain a value.

CROSS REFERENCE: Description 3.1;

Maintenance 19.14.

Table 13.1. — Conversion factors for adjusting

windspeeds taken at heights in excess

of 20-foot standard height

Height of anemometer

above 20-foot standard Conversion factor

(Feet)

0 1.00

10 .95

20 .91

30 .88

40 .86

50 .84

60 .82

70 .81

80 .80

105 .78

130 .75

180 .72 Figure 13.4. — Face wind and cover top stem with

finger to measure winds in excess of 10 m.p.h.

76
CHAPTER 14

RAIN GAGES

14.1 THE STANDARD

8-INCH RAIN GAGE

The following operating instructions apply

to both the large capacity and the smaller capacity FS standard 8-inch-diameter rain gages:

Measuring Normal Amounts of Rain

1. Remove collector from top of the rain

gage (fig. 14.1A).

2. Use a clean measuring stick and slowly

lower it straight into the measuring tube (fig.

14.1B.).

3. Remove the stick before water has a

chance to creep up above the actual waterline.

4. Read the stick in inches and hundredths

(fig. 14.IC). Normally, a precipitation measurement of less than one-half of 0.01 inch is

recorded as a trace (T).

5. Empty the measuring tube (fig.14.ID)

and replace it in the gage.

6. Replace the collector, making sure it

rests squarely on top of the gage (fig. 14.IE).

Measuring Rain Where Measuring

Tube Has Overflowed

1. Record a full tube as 0.50 inch if FS gage

or 2.00 inches if traditional, large capacity

gage.

2. Carefully lift the tube out and dump the

water (fig. 14.2A).

3. Pour the water from the overflow cylinder into the measuring tube (fig. 14.2B).

4. Measure and record the amount if less

than full tube. Repeat if necessary until all the

water in the overflow cylinder has been measured.

5. Record the total of all the measurements

taken.

Night or Early Morning Rains

To prevent loss by evaporation, measure

night or early morning rains as soon as possible

after rain stops. At the basic observation time,

record the total of all measurements since the

previous day's observation time.

Measuring Procedure When Ice

or Snow Is Expected

1. Remove the collector and the measuring

tube and store in a convenient place.

2. Leave the overflow cylinder in place to

catch the precipitation.

3. Measure snowfall as soon as possible

after ending. This will reduce-the chance of

error due to melting and evaporation under

sunny conditions.

4. At measuring time, warm the overflow

cylinder just enough to melt collected snow or

ice but not enough to evaporate any water.

5. Pour the water into the measuring tube;

then, measure and record.

6. If there is a large amount of snow or ice

in the overflow cylinder, melting in the overflow cylinder can be speeded by carefully pouring in a known amount of hot water from the

measuring tube. Subtract this known amount

77
lC'.:-'..~:.i,^'Ú^M tm ^^Mf-t Di^^BSIhtr*U L: Hfl ■■ £

Figure 14.1. — Measuring normal amounts of rain with FS rain gage: A, Remove collector; B, dip measuring stick

into inner tube; C, read stick; D, empty tube; E, replace collector.

78
Figure 14.2. —Procedure when measuring tube overflows: A, Dump full tube and record 0.50 inch;B, pour excess

into tube and measure.

from the total water poured out of the overflow cylinder.

Using a Snowboard to

Measure Snowfall

Snowfall should be measured as soon after

ending as possible. This may eliminate errors

caused by the snow settling and becoming more

compact.

1. Measure depth of new snow on board

(cleared prior to snowfall) to nearest tenth of

an inch.

2. Measure depth of accumulated snow to

nearest tenth of an inch. (Total snow depth is

often measured on nearby representative

ground rather than on the snowboard.)

3. Using overflow can from 8-inch rain gage

(as one would use a cookie cutter), position it

over the new snow and press the can down to

the snowboard.

4. Clear snow from around the overflow

can.

5. Slide a sufficiently large sheet of cardboard or metal under the mouth of can, keeping good contact. Then turn can and sheet upright, tap or slide sheet to shake all of snow core

into can, and remove sheet.

6. Melt the collected snow, pour the resulting water into the measuring tube from the rain

gage, and measure water equivalent with rain

gage measuring stick.

CROSS REFERENCE: Description 4.1; Installation and Exposure 8.8; Maintenance 22.

14.2 THE 4-INCH CLEAR

PLASTIC GAGE

Measurement techniques are similar to those

for the standard 8-inch gage except the level of

water is read directly from the scale etched on

the measuring tube (fig. 14.3). Be sure gage is

positioned vertically before reading the scale. If

more than 1 inch of rain occurs, causing the

measuring tube to overflow, follow the procedure in section 14.1.

CROSS REFERENCE: Description 4.1;

Maintenance 22.1.

79
Figure 14.3. — Read amount of rainfall directly from scale on clear plastic g£^es: Left, 4-inch clear plastic gage;

center, wedge-shaped gage; ríg/zí, small orifice gage.

14.3 THE WEDGE-SHAPED GAGE

Make sure gage is positioned vertically and

simply read the level of water directly from the

scale etched on the gage (fig. 14.3). Measure

precipitation as soon as possible after it occurs

in order to reduce error due to evaporation

losses.

CROSS REFERENCE: Description 4.1;

Maintenance 22.1.

14.4 WEIGHING TYPE EQUIPPED

WITH CLOCK DRIVE

1. Use the pen arm shifter and lift pen from

chart.

2. Remove collector and bucket (fig.

14.4A). If there is water in the bucket, check to

see if it was recorded on the chart. Empty

bucket and replace (fig. 14.4B).

3. Remove chart drive cylinder and take off

old chart. Note date and "time off." Prepare

fresh chart by noting station name, date, and

"time on" (fig. 4.7).

4. Install the fresh chart. Make sure it fits

snugly and that it rests squarely on the lower lip

of the cylinder (fig. 14.4C).

5. Wind the clock but do not overwind it

(fig. 14.4D).

6. Replace chart drive cylinder and turn it

counterclockwise until the correct time line on

the chart is opposite the pen.

7. Refill the pen with ink. If necessary,

draw a piece of hard paper through the nibs to

start the flow of ink. A small corner piece of

chart paper works fine.

8. Return pen to chart using pen arm

shifter.Make final time adjustment if necessary.

9. Check pen setting for zero. The pen

should rest on the bottom horizontal line ofthe

chart (zero) when empty bucket is in place (fig.

14.4E). Make necessary adjustments in zero by

using the fine adjustment thumbscrew.

10. Replace collector and close gage.

The above procedure assumes chart changes

at the end of each chart scale period; i.e.,

24-hour charts are changed each day, 7-day

charts are changed each week.

Unless large precipitation amounts occur,

charts having a 24-hour scale may be left on for

a week if the pen is advanced slightly upward to

a new line every day, with the date and time

notations made. There should be a new starting

line for the pen each day regardless of whether

or not any precipitation has fallen.

80
fr ' Figure 14.4. — Weighing rain gage operation: A, Re- ^j

move collector; B, empty bucket; C, install fresh

chart;D, wind clock; £, zero pen.

81
Special Instructions for Use

During Freezing Weather

1. Remove the funnel attached to the bot^

torn of the collector and store it in a convenient

place.

2. Place an antifreeze solution in the

bucket. One such solution recommended by

the National Weather Service consists of a mixture of 2 pounds commercial anhydrous calcium chloride (77 to 80 percent pure); IV4 to IV2

quarts water, at room temperature; and 2

ounces SAE 10 motor oil.

A commercial type of ethylene glycol preparation such as Prestone has been recommended

as an alternative to the National Weather

Service solution described above (Kidd 1960).

Despite its higher cost, this type of preparation

has the advantage of being noncorrosive (it

actually provides a protective coating). It has

the further advantage of minimizing the chance

of top freezing since it does not have the settling tendency of the calcium chloride solution.

A small amount of SAE 10 motor oil should

be added to the antifreeze to prevent evaporation if the gage is not checked daily.

3. Addition of the antifreeze will raise the

zero of the pen arm. Note the level ofthis new

zero. Using the fine adjustment thumbscrew,

raise or lower the zero until the pen rests on the

nearest horizontal chart line. This will aid in

figuring precipitation amounts.

4. Let precipitation accumulate in the

bucket until the antifreeze becomes too

diluted to prevent freezing. When this occurs,

empty the bucket and refill with a fresh

solution.

CROSS REFERENCE: Description 4.1; Installation and Exposure 8.9; Maintenance

22.3.

82
CHAPTER 15

FUEL MOISTURE

SCALES

15.1 THE APPALACHIAN SCALE

The procedure for measuring the moisture

content of the 1/2-inch ponderosa pine fuel

moisture stick is as follows:

1. Check the scale. — Be sure that the sliding weight on the balance arm is set and

locked at 100 grams. The weight is locked by

tightening the set screw on top of the weight.

Check calibration by hanging the 100-gram

weight on the hook. Tap the pivot block

lightly; the pointer should indicate zero (fig.

15.1). If adjustment is necessary, loosen the

wing nuts and carefully move the scale until

the pointer indicates zero.

2. Remove the stick. — Use a clean glove,

piece of cloth, or paper and remove the stick

from the wire rack. If dry, lightly brush away

any dust, using a clean, soft bristle paint

brush (fig. 15.2). If stick is wet, shake away

any free moisture.

3. Weigh the stick. — Hang the stick on

the scale arm (fig. 15.2). Steady the stick and

let the pointer come to rest. As soon as the

pointer comes to rest, tap the pivot block to

overcome premature stopping due to friction;

if windy close the shelter door (fig. 15.2)

Then read the moisture content percent directly on the curved scale opposite the

pointer, and record the results. Read the scale

to the nearest whole percent (fig. 15.3).

Guard against parallax error when reading

scale.

4. Replace the stick. — Remove the stick

from the scale and return to the wire racks.

Make sure the same side faces up (brads down)

andthescrew hook end points north (fig. 15.4).

CROSS REFERENCE: Description 5.1,

5.3; Installation and Exposure 8.11; Maintenance 23, 24.1.

Figure 15.1. — Use a 100-gram test weight to check the

calibration of the Appalachian scale.

83
Figure 15.2. — Weighing the stick: Left, Remove dust, dirt, etc.; center, carefully hang stick on scale; right, close

door to protectstick from wind.

Figure 15.3. — This stick weighs 108 grams so the

moisture content is 8 percent as indicated by the

pointer.

Figure 15.4. — Replace stick on wire rack, hook north,

brads down.

15.2 CHISHOLM PORTABLE SCALE

This scale can be hand held (fig. 15.5) but

is much easier to use if it is hung on a post,

tree, etc. To operate:

1. Check the scale. —Make sure that it is

plumb and that the pointer moves freely.

Check calibration with a 100-gram test

weight.

2. Remove the sijcfe.—Using a clean

glove, piece of cloth, or paper, remove the

stick from the wire rack. If dry, lightly brush

dust off, using a good quality, soft bristle

brush (fig. 15.2). If wet, shake off any free

moisture.

3. Weigh the stick. — Carefully hang the

stick on the hook provided. Gently tap the

pointer. Read the moisture content percent

from the graduated scale as indicated by the

pointer (fig. 15.5).

4. Replace the siicfe. — Return to wire

racks making sure that the same side is up

(brads down) and the screw hook points

north (fig. 15.4).

CROSS REFERENCE: Description 5.1,

5.3; Maintenance 23, 24.4.

15.3 WILLIAMS POCKET SCALE

1. Remove locking screw and cover.

2. Insert locking screw as handle.

3. Calibrate the scale by hanging cover

(100 grams) on hook (fig. 15.6); any offset

must be considered before recording the final

value.

84
^-'%idfe/^«> *%

Figure 15.5. — Weighing fuel moisture stick on

Ciiisiiolm portable scale. This stick weighs 104.25

grams so its moisture content is 4 percent as indicated by the pointer.

4. Remove cover and hang stick on the

hook (fig. 15.7).

5. Turn circular weight until beam balances; at this point make sure the scale body

is horizontal and the handle vertical.

6. Determine moisture content percent by

adding together the reading from the scale on

the rotating weight and adjusting the reading

from the scale on the body (fig. 15.7). Recheck to make certain the figures are being

read in the proper direction on the rotating

scale.

CROSS REFERENCE: Description 5.1,

5.3; Maintenance 23, 24.3

15.4 TRIPLE BEAM BALANCE

1. Check the balance. —Dust off the balance pan using a clean, soft bristle paint

brush. Place a 100-gram weight on the pan

Figure 15.6. —Check calibration of scale by usii^

cover as a 100-gram test weight.

TOTAL WEIGHT

111.7 GM.

MOISTURE CONTENT

12 PERCENT

Read 1.7gm.Here

Read 110 gm. Here

Figure 15.7. — Weighing fuel moisture stick on

Williams pocket scale. This stick weighs 111.7 grams

so moisture content is 12 percent as indicated on

scale.

85
Figure 15.8. — Checking the balance of triple beam

balance.

lad 4.8 gm. Here^

Read 100 gm. Here«

TOTAL WEIGHT

104.8 GM.

MOjUSWRE CONIJNI

5 PERCENT

Figure 15.9. — Weighing fuel stick with triple beam balance. This stick weighs 104.8 grams thus indicating a

moisture content of 5 percent as indicated on first

scale bar.

and balance at 100 grams instead of at zero

(fig. 15.8).

2. Remove the stick. — Use a clean glove,

cloth, or piece of paper and remove the stick

from the wire rack. If dry, lightly brush away

any dust. Use a clean, soft bristle paint brush.

If stick is wet, shake away any free moisture

(fig. 15.2).

3. Weigh the stick. — Lay the center of the

stick across the center of the balance pan (fig.

15.9). Move the two large weights across their

respective beams until the pointer swings freely. Be sure that the weights are seated in the

notches of the beams. Now adjust the small

sliding weight on the front beam until the

pointer swings the same distance above and

below the zero mark on the small vertical

scale at the end of the pointer.

In case the balance is sluggish in its action,

always tap the main bearing case with a finger

or pencil so that the pointer will not settle

prematurely in the wrong place.

Read the scale and record the weight of

the stick in excess of 100 grams.

4. Replace the stick. — Return the stick to

its wire rack making sure same side faces up

(brads down) and screw hook pointing north

(fig. 15.4).

Move all balance weights to zero.

CROSS REFERENCE: Description 5.1,

5.3; Maintenance 23, 24.5

15.5 HARVARD BALANCE

The operation of the double pan Harvard

balance is similar to that of the triple beam

balance except for the manipulation of the

weights. To weigh the stick, place it on one of

the pans and add a 100-gram weight to the

other pan (fig. 15.10). Now add additional

small weights to the pan untilthe vertical pointer swings freely. Use the sliding weight on the

front scale to achieve final balance.

CROSS REFERENCE: Description 5.1,

5.3;Maintenance 23, 24.6.

Figure 15.10. — Weighing fuel stick with Harvard balance. This stick we^hs 105.7 grams thus indicating a

moisture content of 6 percent as indicated on scale.

86
PART 4.

MAINTENANCE OF

/ ^^^^B

'-^

FIRE-WEATHER INSTRUMENTS/ #)

Proper maintenance is the final ingredient

for consistently accurate fire-weather observations. It is unreasonable to expect an instrument in poor operating condition to provide

acceptable data. It is equally unreasonable to

expect an instrument to be in good operating

condition when it has not been subjected to a

program of continuous maintenance.

The question of whom should do the instrument maintenance job is an important one.

Quite often routine daily maintenance will be

accomplished by the observer while the more

detailed periodic or annual maintenance job

will be assigned by a person who is skilled and

experienced in the maintenance of instruments. Agencies that have electronic or radio

technicians on the staff often assign the bench

maintenance of weather measurements to

9-270 O - 76 - 7

87
them. Some agencies train a fire control technician specifically for the instrument maintenance task and accomplish this work at a central location during the nonfire season months.

If an agency lacks personnel trained in the

proper skills they can send instruments back to

the factory (usually an expensive alternative)

or contract the job to local sources such as

watch repairmen or radio-TV repairmen.

Regardless of how maintenance is accomplished, however, it is very important that it be

done by people who understand instruments

and will not ''tinker" with the instruments or

"maintain them to death."

A program of continuous maintenance for a

fire-weather instrument should include:

1. Daily and periodic maintenance, as

needed, throughout the service life of the instrument. This should include routine cleaning,

lubrication, calibration checks and adjustments, and prompt repair or replacement of

worn or broken parts. This can often be accomplished by the observer.

2. Annual or semiannual inspection and

general service. At this time the instrument

should be brought to the workbench, taken

apart, and closely inspected for signs of wear

and tear. This is a job for the trained technician

who knows what he is doing. Like most everything else, weather instruments do wear out.

Don't try to keep them forever. Replace beatup, or even obsolete instruments!

3. Following repair or replacement of worn

or broken parts, the instrument should be carefully tested to insure that all components are

operating properly and that it is precisely

calibrated.

4. If the instrument is not put back in service immediately following the annual check, it

should be properly stored until needed again.

Like so many other jobs, maintenance of

fire-weather instruments is easier and more efficient if the proper tools are readily available. In

the case of periodic maintenance, the presence

of the right tool or service item at the right time

will often determine whether or not it is possible to perform the required maintenance. For

this reason, a tool cache should be provided at

the fire-weather station. A small, weatherproof

box attached to a fencepost or the anemometer

pole (fig. 8.11) can easily serve this purpose

(see section 8.6). The following items should be

included in such a tool cache:

1. Clean wiping cloths.

2. Assorted soft brushes for dusting instruments, hygrothermograph hairs,

and fuel sticks.

3. Needle-nose pliers.

4. Small and medium sized screwdrivers.

5. Medium sized carpenter's level.

6. Anemometer oil.

7. Light instrument oil (sewing machine

oil, gun oil, etc.).

8. Hygrothermograph ink.

9. Hygrothermograph and rain gage

charts.

10. Clean psychrometerwicking.

11. Heavy duty white thread.

12. Small, sharp scissors or single-edged

safety razor blade.

A more complete tool kit is required for annual or bench maintenance. In addition to the

above list, the following items should be available at an instrument repair and maintenance

workbench:

1. Supply of fresh batteries.

2. Extra thermometers.

3. Nonflammable instrument cleaning

solvent.

4. Toothbrushes.

5. Continuity tester.

6. Anemometer calibrator.

7. Soldering gun and rosin core solder.

8. Crocus cloth.

9. Special lubricants.

10. Hygrothermograph hair elements.

11. Hygrothermograph and rain gage pens.

12. Lampblack oil color.

13. Hard-finish paper.

14. Compressed air.

Maintenance instructions for the instruments most likely to be used for fire-weather

observation are included in the pages that follow. General maintenance instructions that

apply to all instruments of a given type as well

as specific maintenance instructions for specific makes or models are given.

Although these instructions are set down in

a step-by-step fashion, the user is cautioned to

read through the entire section of interest before attempting to use the instructions cookbook fashion during actual maintenance.

88
CHAPTER 16

THERMOMETERS

Care is the byword in maintenance of thermometers, which are very fragile instruments.

Whenever possible, handle the thermometer in

its mounting plate. Be especially careful not to

strike the bulb against anything.

Thermometer maintenance is mainly concerned with cleaning, restoring obscured markings, and the most important task of recognizing and correcting defects.

16.1 CLEANING

The thermometer and its mounting plate

should be kept clean. This can be accomplished by regular dustings with a soft brush.

Periodically the thermometer should be removed from the mounting plate and both the

thermometer and the mounting plate washed

with soap and water. Vinegar or a nonflammable cleaning solvent may be used to remove

stubborn dust or corrosion provided that the

thermometer is subsequently rinsed in clean

water.

16.2 RESTORING WORN MARKINGS

1. Broken constrictions on standard maximum thermometers.

2. Separated alcohol or mercury columns

on all thermometers.

Fractured Maximum Thermometers

It was mentioned previously that the maximum thermometer has a constriction in the

capillary, just above the bulb. This constriction

allows the mercury to expand upward as the

temperature rises but does not allow the mercury to retreat into the bulb when the temperature drops. The mercury trapped above the

constriction is free to float in the capillary;

this is not a defect. Because of this floating

tendency, however, the thermometer must

be slowly lowered to the vertical position

before reading. If the thermometer is

abruptly lowered from the horizontal to the

vertical position, a floating column might

slam down against the constriction to fracture it. The constriction can be similarly

damaged during resetting by spinning the

thermometer while the column is floating

above the constriction.

Thermometer markings often become obscured over time and are consequently hard to

read. Obscured markings can be renewed by

spreading a small amount of lampblack oil color on the stem and then immediately rubbing

off the excess with a piece of hard-finish paper.

Art supply shops and many paint stores carry

the lampblack oil color needed to do this job.

16.3 THERMOMETER DEFECTS

Thermometers should be checked periodically for two types of defects (fig. 16.1).

NORMAL

CONSTRICTION

2SS2ai^'°'^teS5SSI!Z23S!l '

NORMAL

ALCOHOL CAPILLARY

S)

FRACTURED

CONSTRICTION

SEPARATED

ALCOHOL CAPILLARY

Figure 16.1 —Thermometer defects: Top, Normal

and fractured constrictions in maximum thermometers; bottom, normal and separated alcohol capillaries in minimum thermometers.

89
The result of a fractured constriction is that

the mercury is now able to retreat through the

constriction into the bulb. This is a defect and

such a thermometer, sometimes called a ''retreater," should be replaced.

Fractured constrictions on maximum thermometers are often hard to detect; but these

malfunctions should be suspected whenever

the maximum temperature consistently reads

more than 1° F. lower than the reading on the

thermometer when set at the previous

observation.

Separated Columns

A separated column is one in which portions

of the fluid become separated from the main

column. Column separation is common in all

thermometers, especially after shipping or

other situations where they receive excessive

shaking. In alcohol thermometers, column separation may also be caused by the condensation

of alcohol vapor in the upper part of the bore.

Separated alcohol and mercury columns can

usually be reunited by one of the following procedures:

1. A very quick and easy method is to attach the thermometer, in its mounting plate,

to a sling psychrometer handle to which is fastened IV2 feet of chain, wire, or thin nylon

rope. Make sure that sufficient clearance exists

and then vigorously sling the thermometer as

you would a sling psychrometer.

2. Hold thermometer securely in your hand

by curling your fingers and thumb around the

edges of the mounting plate. Be sure that the

bulb end points away from the body. Do not

touch or press on the glass tube itself, or it may

crack during shaking. Shake down with a long

sweep, ending abruptly. Make sure you have

sufficient clearance from obstructions.

3. Lay out a small cushion of newspapers or

magazines, or similar object with some "give."

Take thermometer, in its mounting plate,

check that all mounting screws are tight, and

with bulb end down tap the thermometer lightly. The detached drops should gradually unite

with the main column. Do not tap too hard or

the small nub at the upper end of the thermometer may break off from the stem. After successfully reunitingthe column, let the thermometerstand vertically in a warm place for an hour

so that any remaining droplets have a chance to

drain down to the main column.

4. As a last resort, heat can be applied to

the thermometer bulb. This is best accomplished by holding the thermometer bulb in a

pan of water which is being slowly heated. Be

sure to remove bulb from water before column

reaches top of tube. Remember that the column will continue to rise briefly after removed

from the water.

a. For an alcohol thermometer, continue to heat the bulb in the above manner until the main column enters but

does not completely fill the small air

chamber or bulb at the top of the

stem. This should drive all the air bubbles up the stem and into the air chamber where they should rise above the

alcohol. Do not let the alcohol completely fill the air chamber — it can

blow the top off the thermometer, or

blow out the bulb, depending on

which is weaker.

After all the bubbles have been removed by this method, remove the

thermometer from the water and hang

it, bulb down, to cool. This will

allow any liquid which may have clung

to the sides of the bore to drain

down into the column.

b. If a mercury thermometer and a small

amount of mercury is separated from

the top of the main column, heat in

the same manner as prescribed above

until a small amount of mercury

enters the small bulb. Holding this

temperature, quickly tap a few times.

Remove from water and as the mercury drops see if column is reunited; if

not, repeat. Do not let the mercury

completely fill the air chamber as it

can blow out the top or bulb of the

thermometer.

If the amount of mercury above the

separation is more than the upper air

chamber can hold, a slightly different

procedure should be followed. If available, first cool the bulb only in dry ice

until all the mercury is in the large

lower bulb. Then carefully tap bulb

end of the thermometer gently to

90
bring all bubbles to the top. Now

allow bulb to warm slowly.

Specific instructions for maintenance of

wet- and dry-bulb thermometers are discussed

in chapter 18. Specific instructions for several

types of maximum-minimum thermometers

follow.

16.4 STANDARD MAXIMUMMINIMUM THERMOMETERS

EQUIPPED WITH

TOWNSEND SUPPORT

Refer to figure 16.2.

Annual Maintenance

Thermometers

1. Remove the thermometer retaining strip

and screws (E) £ind lift the thermometers from

their mounting plates (D). Be careful not to

lose the tiny retaining screws.

2. Use soap and water to clean the thermometers and mounting plates. Remove stubborn dirt or corrosion with instrument cleaning

solvent or vinegar.

3. Carefully check thermometers for defects (see section 16.3). Repair or replace as

necessary.

4. If markings on thermometers are obscure, renew according to instructions in

section 16.2.

5. Secure thermometers in their mounting

plates.

Townsend Support

Refer to figure 16.3.

6. Remove the screw (A) holding the spinning clamp (B) to its shaft (D). Slide off spinner

(B) from shaft (D).

7. Wash thoroughly with a nonflammable

instrument cleaning solvent.

8. Clean out oil hole (C) on spinner.

9. Put a drop of light instrument oil on

spinner shaft (D) and replace spinner (B).

Periodic Maintenance

1. Add a drop of oil through the oil hole (C)

on the spinner (fig. 16.3) as needed.

2. Check both thermometers for defects,

Figure 16.2. — Standard maximum-minimum thermometer mounted in Townsend Support: A, Minimum thermometer; B, maximum thermometer; C,

Townsend Support; D, thermometer mounting

plate; E, thermometer retaining strip and screws; i^,

Townsend Support thumbscrew.

Figure 16.3. — Unassembled Townsend Support: A,

Spinner clamp retaining screw; B, spinning clamp;

C, oil hole; D, spinner shaft; E, upper clamp; F,

thumbscrew.

i.e., fractured constrictions, separated column,

etc. (see section 16.3).

3. Check thumbscrews (F) on clamps for

tightness.

4. Dust thermometers with a soft brush to

remove any accumulated dirt.

CROSS REFERENCE: Description 1.1; Installation and Exposure 8.2; Operation 10.1,

10.2.

16.5 COMBINED (SIX'S) MAXIMUMMINIMUM THERMOMETER

(Taylor, Weksler, and similar models)

Refer to figure 16.4.

Annual Maintenance

1. Remove upper and lower thermometer

retaining strips (B) and very carefully lift out

the thermometer tube (C).

91
Figure 16.4.— Combined maximum-minimum thermometer; Left, Assembled; right: A, mounting plate; £, thermometer retaining screws and strip; C, thermometer tube;£>, magnet.

2. Clean thermometer and its mounting

plate (A) with soap and water. Use instrument

cleaning solvent or vinegar to remove stubborn

dirt or corrosion from thermometer tube.

3. Return thermometer tube to the mounting plate and secure with the thermometer retaining strips.

4. Inspect thermometer for defects.

a. If column is separated, grasp the instrument firmly in hand with bottom

of "U" tube pointing toward ground.

Curl fingers and thumb around

mounting plate; do not touch or press

on glass tube itself as it may crack during shaking. Now swing hand forcefully downward in an arc. Do this

until the columns reunite.

b. If either of the index rods settles into

its mercury column, attempt to correct by the same procedure given

above,

c. Conduct the following procedures if

either index has been forced into

either of the expansion chambers (the

large bulbs) at the tops of the thermometer tube: First, attempt to draw

the index out using the magnet (D). If

this doesn't work, gently tap the bulb

in order to manipulate the index at

least partially into the bore and then

draw it all the way into the bore with

the magnet.

Periodic IVIaintenance

1. Check for defects whenever instrument

is reset.

2. Dust tube with a soft brush to remove accumulated dirt.

CROSS REFERENCE: Description 1.1;

Operation 10.1,10.3.

92
CHAPTER 17

PSYCHROMETERS

Psychrometers are rather delicate instruments and as such require careful handling and

conscientious maintenance. Maintenance consists primarily of regular wick replacement, regular cleaning, periodic lubrication on electrical

units, and repair or replacement of worn parts

as necessary. Psychrometer maintenance

should be continuous while the instrument is in

use. Annual maintenance is simply that part of

this continuous maintenance when general refurbishing and a more thorough cleaning and

lubrication are performed.

17.1 THE WET-BULB WICK

The most serious deficiency in psychrometer maintenance is failure to replace the wetbulb wick before it gets dirty; unfortunately

this is also the most common oversight. A clean

wick is essential for accurate wet-bulb readings

and should be replaced at the first sign of dirt,

crust, or discoloration but at least every 2

weeks regardless of how clean it may appear.

Only clean, distilled water or other clean, mineral-free water should be used to wet the wetbulb wick.

Procedure for replacing a psychrometer

wick (fig. 17.1):

1. Remove the old wick using a razor blade

or fine-point knife or scissors.

2. Wash hands with soap and water. Rinse

thoroughly in clean water.

3. Cut a 3- to 3V2-inch length of clean

wicking.

4. To remove sizing, wash the new wick in

distilled or other mineral-free water.

5. Clean the lower part of the stem and the

bulb of the wet-bulb thermometer. Then wash

with vinegar to remove stubborn mineral deposit and rinse in clean water.

6. Slip the new wick over the wet bulb to a

point on the stem just below the lowest graduation on the stem, about 1 inch above the top of

the bulb.

7. Using an extra strength white sewing

thread, tie the wick to the thermometer as follows (fig. 17.1):

a. First, tie wick near the upper end,

about 1 inch above the top of the

bulb.

b. Second, tie wick in the middle, immediately above the top of the bulb.

Be sure to stretch the wick downward

93
Figure 17.1. — A properly installed psychrometer

wick.

as the knot is tightened to assure a

snug fit against the thermometer

stem.

c. Third, tie wick immediately below the

end of the bulb. To insure a snug fit,

make a loop of thread to form a knot

and slip it up around the tip of the

bulb, just where it begins to round off.

Carefully draw the knot tight causing

the loop to slip off the tip of the bulb,

thereby stretching the wick snugly

against the thermometer bulb and at

the same time securing it firmly.

d. Using a razor blade or fine-point knife

or scissors, trim loose ends of knots as

well as all wicking in excess of 1 inch

below lower tip of the wet bulb.

If temporarily out of clean wicking, the

dirty wick can be removed, washed in soap

and water, rinsed thoroughly in clean distilled or other mineral-free water, and replaced. One or two wraps of clean gauze

bandage, neatly tied over the bulb, can also

serve as a temporary measure. White shoelaces, rinsed in clean distilled water, can also

be a satisfactory substitute.

17.2 WET- AND DRY-BULB

THERMOMETERS

Maintain wet- emd dry-bulb thermometers

in accordance with the instructions in sections

16.1 through 16.3. An important item of

psychrometer maintenance is assuring that the

thermometers agree within one-half graduation when both are read as a dry bulb. For

example, if the thermometers have 1° F. graduations, they should read within 1/2° F. of

each other when read prior to wetting the

wet-bulb wick.

When replacing a broken thermometer on a

psychrometer, be sure the replacement

matches exactly the accuracy of the unbroken

mate. To insure identical accuracy, it is usually necessary to replace both thermometers

with a new matching pair. When replacing

thermometers remember the wet bulb always

hangs below the dry bulb. Make sure you put

the wick on the bulb that hangs the lowest.

This minimizes the chance of moving moist

air across the dry bulb during ventilation.

17.3 CLEANING

Psychrometers, especially those constantly

exposed in instrument shelters, require regular

cleaning. Cleaning can be accomplished by

using a camel's hair or other soft bristle brush

to remove accumulated dust before each use

of the psychrometer.

Specific maintenance instructions for

psychrometers commonly used for fireweather observations follow.

17.4 ELECTRIC FAN

PSYCHROMETER

(Forester Model 9X060 and Weather

Measure Model HM20)

Refer to figure 17.2.

Annual Maintenance

1. Remove spacer screw (K) and lift thermometer mounting plate (A) from the support bracket (F). Carefully remove thermometers from the mounting plate. Be careful not

to lose the tiny retaining screws. Inspect thermometers according to the instructions of sec94
tions 17.2 and 17.3 and repair or replace as

necessary.

2. Remove and discard wet-bulb wick (E)

and carefully clean both thermometers and

the mounting plate (A). Use a nonflammable

cleaning solvent or vinegar to remove stubborn dirt and corrosion. Rinse with clean

water.

3. If necessary, renew thermometer

markings according to instructions in section

16.2.

4. Carefully replace thermometers in

mounting plate. Be sure they are firmly

mounted.

5. Install a clean wick on the wet bulb

(C) following the procedures in section 17.1.

6. Clean the motor (H) and fan (G), but

do not attempt to disassemble the motor.

7. Apply a drop of oil to the fan shaft

bearings (G) and wipe off excess. Use anemometer oil or other light, nongumming instrument oil such as sewing machine oil.

8. Check and, if loose, tighten all mounting screws, fan hub setscrew, and electrical

connections.

9. Install a fresh 6-volt lantern battery.

Turn motor "on" and check to see if fan is

blowing air across the thermometer bulbs

(away from the fan). If the air is being sucked

into the fan, reverse the connecting wire leads

on the battery.

10. On motor units with a thrust plate,

check for proper adjustment of the thrust

plate (I). Turn the motor "on" and carefully

bend the thrust plate to the point where the

greatest r.p.m. is realized.

11. If the fan will not operate, check the

battery, the electrical connections, and the

switch. If trouble is not apparent, replace the

motor.

12. If instrument is not to be put in immediate service, disconnect the battery from

the motor.

fK

Figure 17.2. — Forester 9X060 electric fan psychrometer (left) and Forest Service electric fan psychrometer

(right): A, Thermometer mounting plate; B, thermometer retainii^ screws and clip; C, wet-bulb thermometer; D, dry-bulb thermometer; E, wet-bulb wick; F, support bracket; G, fan and shaft; H, motor; /, thrust

plate; J, fan bushing; K, spacer screw.

95
Periodic IMaintenance Whiie in Use

Maintenance At Least Every 2 Weeks

1. Replace wet-bulb wick (see section

17.1).

2. Remove all dust with a camel's hair

brush.

3. Oil the fan shaft bearings if necessary.

4. Check all screws and tighten if loose.

5. Check battery and replace at first sign

of weakness. (A 6-volt lantern battery may

last up to 6 months with once-a-day use.)

6. Check water container and clean if

dirty or if scum is forming on side.

Daily iVIaintenance

Before Each Use

1. Brush off any dust or dirt that may

have accumulated since last use.

2. Check to see that thermometers agree

within 1/2° F. when both are read as dry bulbs.

3. Check the wick and replace it if there is

any sign of dirt or discoloration.

4. Check water container. If water is dirty

or if scum is forming on the container, clean

and refill.

CROSS REFERENCE: Description 2.2; Installation and Exposure 8.3; Operation 11.1,

11.2.

17.5 HAND FAN PSYCHROIViETER

(Forester Model 9X050)

Refer to figure 17.3.

Annual Maintenance

1. Remove spacer screws (L) and lift

thermometer mounting plate (A) from the

support bracket (F). Carefully remove thermometers from the mounting plate. Be careful not to lose tiny retaining screws (B). Inspect thermometers according to instructions

in sections 16.2 and 16.3 and repair or replace

as necessary.

2. Remove and discard wet-bulb wick (E)

and carefully clean both thermometers and

the mounting plate (A). Use a nonflammable

cleaning solvent or vinegar to remove stubborn dirt and corrosion. Rinse with clean

water.

3. If necessary, renew the thermometer

markings according to instructions in section

16.2.

4. Carefully replace thermometers in

mounting plate. Be sure they are firmly

mounted.

5. Install a clean wick on the wet bulb

following the procedures in section 17.1.

6. Clean the fan unit.

7. Oil the crank shaft (M) with a drop of

oil in the hole (N) on top of the bearing.

8. Put a drop of oil on the fan shaft. To

gain access to this shaft, spring its supporting

strap steel away from the drive wheel (I) and

slip the fan (G) off.

9. Inspect for slippage between the drive

wheel and the hub of the fan shaft. If there is

too much slippage, increase tension by tightening the tension screw or bending the fan

support.

10. Inspect the hub of the fan shaft. If the

hub is badly worn, remove the fan blade and

Figure 17.3. — Hand fan psychrometer: A, Thermometer mounting plate; B, thermometer retaining

screw and clip; C, wet-bulb thermometer; D,

dry-bulb thermometer; E, wet-bulb wick; F, support bracket; G, fan and shaft; H, fan pulley; /,

drive wheel; J, fan pedestal; K, crank; L, spacer

screw; M, crankshaft; N, oil hole.

96
hub. Turn the hub over and replace it and the

fan blade. This will allow the drive wheel to

engage the unworn groove in the fan shaft

hub.

Periodic IVIaintenance

Maintenance At Least Every 2 Weeks

1. Replace wet-bulb wick (see section

17.1).

2. Remove all dust with a camel's hair

brush.

3. Put a drop of oil on the crankshaft and

a drop on the fan shaft.

4. Tighten all screws. Make sure unit is

firmly mounted to floor of instrument

shelter.

5. Check water container. If water is dirty

or if scum is forming on the container, clean

and refill.

Daily i\/laintenance

Before Each Use

1. Brush off dust and dirt.

2. Check to see that thermometers agree

within 1/2° F. when both are read as dry bulbs.

3. Check the wick and replace it if there is

any sign of dirt or discoloration.

4. Check water container. If water is dirty

or if scum is forming on the container, clean

and refill.

CROSS REFERENCE: Description 2.2;

Operation 1.1, 11.4.

17.6 PORTABLE ELECTRIC

FAN PSYCHROMETER

(Bendix Psychron Model 566 and

Gemware Model Electro V)

Refer to figure 17.4.

Periodic IVIaintenance

The timing and extent of maintenance on

portable electric psychrometers depends on

the type and amount of use.

Cleaning should be a continuous maintenance item and lubrication should be done at

least monthly if the instrument receives daily

use. The wick should be changed at the first

sign of dirt or discoloration but at least every

2 weeks while in regular use.

Figure 17.4. — Portable electric fan psychrometers:

A, Air intake; B, dry-bulb thermometer; C, retaining strip; A thermometer holder; E, air intake

cylinder; F, fan and motor; G, wet-bulb thermometer and wick; H, psychrometer housing; /, retaining screw; J, thermometer holder shaft; K, sliding

door; L, switch; M, motor mounting screws; N,

motor mounting plate; O, fan shaft; P, housing

screws.

97
The following maintenance instructions

should be performed as needed but at least

once a year if the instrument receives regular

use.

1. Remove sliding air intake (A) and,

while holding the thermometers in place, remove the two thermometer retaining strips

(C).

2. Lift the thermometers out of their

holder (D) and inspect them for defects according to instructions given in section 17.2.

Make sure both agree within 1/2° F. when both

are read as dry bulbs. Repair or replace as necessary.

3. Clean the air intake (A), the air intake

cylinder (E), the thermometer holder, the fan,

and the fan motor. Use a small brush and nonflammable cleaning solvent to remove stubborn dirt.

4. Remove and discard the wet-bulb wick

(G). Carefully clean both thermometers. Use a

nonflammable cleaning solvent or vinegar to

remove stubborn dirt or corrosion. Rinse with

clean water.

5. If necessary, renew thermometer markings according to instructions in section 16.2.

6. Remove the thermometer holder from

the psychrometer housing (H). To remove the

holder from the housing, remove the screws

(I) on top of the holder and in the case of the

Bendix, the shaft (J) at the rear of the holder.

Clean the bottom of the holder and the top of

the housing.

7. Remove sliding door (K) at the rear of

the housing. Remove the water bottle from

upper compartment and the batteries from

the lower compartment. Remove the hard

paper liner from the battery compartment. If

dirty, clean or replace.

8. Replace battery compartment liner

and carefully insert three fresh, heavy-duty,

waterproof, size C flashlight batteries. Hold

housing at a slight angle so that batteries do not

slam against the forward contact. Make sure

that batteries are inserted so that the center

tips are forward.

9. Put one drop of oil on the bottom end

of the fan shaft (0). Put one drop of oil on

the fan shaft between the motor and the fan

blade.

10. Turn switch (L) "on" and check lamp

on top of housing. Replace lamp if necessary.

11. Turn switch "on" and check fan operation. If fan is rubbing against cylinder walls,

turn switch "off," loosen the screws (M) on

the motor mounting plate (N) on the bottom

of the housing. Insert fingers into fan cylinder

and reposition the motor so that the fan

blades clear the cylinder wall.

12. Reattach thermometer holder on top

of housing.

13. Replace thermometers in thermometer

holder. Be sure retaining strips are tight.

14. Install a new wick on the wet bulb

(see section 17.1).

15. Clean the water bottle and fill with

clean, distilled, or other mineral-free water.

Troubleshooting

1. If switch is "on" but light doesn't operate, replace lamp on top of housing (see item

10, above).

2. If switch is "on" and light is very dim,

replace batteries (see item 8, above).

3. If switch is "on" and lamp is lit but fan

does not operate, check to see if fan is hung

up on cylinder wall (see item 11, above).

4. Further troubleshooting requires complete disassembly of the instrument as

follows:

a. Remove sliding air intake (A).

b. Remove thermometer holder (D)

from housing (H).

c. Remove sliding door (K) from rear

of housing.

d. Remove screws (M) from motor

mounting plate (N) on bottom of

housing.

e. Remove screws from side of housing

and carefully pull apart the halves of

the housing.

5. Check all contacts and electrical connections. Use crocus cloth to remove any corrosion. Bend distorted contacts back into

shape. Resolder any loose connections.

6. If neither the lamp nor the motor operate after following the previous instructions,

replace the switch.

7. If, after checking and repairing contacts

and connections, the lamp works but not the

fan, replace the motor.

CROSS REFERENCE: Description 2.2;

Operation 11.1, 11.3.

98
17.7 MORTARBOARD

PSYCHROMETER

(Southern Forest Fire Laboratory

Model)

Refer to figure 17.5.

The mortarboard psychrometer was designed for easy maintenance. Regular cleaning, wick changes, and thermometer maintenance are the main items of concern. Maintenance should be conducted throughout the

service life of the instrument.

Thermometers

1. Follow instructions for thermometer

maintenance in section 17.2.

2. At least every 2 weeks (or when wick is

changed), inspect thermometers to see if they

agree within 1/2° F. when both are read as

dry bulbs. If they do not, repair or replace

with a new matched set.

3. Inspect thermometer bulbs for dirt and

mineral deposit at each wick changing. Remove stubborn dirt with a nonflammable

cleaning solvent or vinegar.

Water Cup

1. Inspect the cap (K) £ind the tubing (J).

The cap should fit tightly on cup (L) and tubFigure 17.5. — Mortarboard psychrometer: A, Upper

radiation shield; B, lower radiation shield; C,

spacer; D, thermometer clip;jE, dry-bulb thermometer; F, wet-bulb thermometer; G, connectors and

couplings; H, support; /, wet-bulb wick; J, plastic

tubing; K, water cup cap; L, water cup.

ing should extend from just above bottom of

cup to 1 inch below tip of wet bulb (F).

2. Wash cup and tube in clean water each

time a fresh supply of wicking (I) is installed.

3. Do not allow the water level in cup to

drop below half full.

Wet-Bulb Wick

Wicking is installed in 28-inch lengths with

the excess coiled in bottom of water cup.

Wick changes are made from this supply as

long as the supply of wicking in the water cup

touches bottom of water cup.

The procedure for installing and changing

the wick is as follows:

1. Before installing a fresh length of wicking (I):

a. Remove old wick.

b. Clean water cup (L) and tubing (J).

c. Clean thermometers.

2. Wash hands and rinse thoroughly.

3. Coil a 28-inch length of fresh wicking

and place in bottom of water cup.

4. Pull end of fresh wicking (I) through

water cup cap (K) and tubing (J).

5. Slip end of fresh wicking over the wet

bulb (F) to a point 1 inch up the stem. Be

sure there are no snags in wick between cup

(L) and wet bulb.

6. The portion of wick covering the wet

bulb should be changed whenever it gets dirty

or discolored but at least every 2 weeks.

7. To change the wick, cut off exposed

portion of wicking halfway between end of

tube and wet bulb. Remove old wicking from

bulb and discard.

8. Pull up a length of fresh wicking out of

the water cup and slip it over the wet bulb to

a point 1 inch up the stem.

9. When supply of wick in water cup no

longer reaches the bottom of the cup, install a

new length of wicking.

Reflective Surface

1. Keep the top surface of the upper radiation shield (A) clean at all times and polish it

periodically (about three or four times a

year).

CROSS REFERENCE: Description 2.2;

Operation 11.1, 11.7.

99
17.8 SLING PSYCHROMETERS

(Standard and pocket models)

Refer to figure 17.6.

Annual Maintenance

1. Remove retaining clips (A) and lift thermometers from mounting plate (B). Remove

wick (E) from the wet bulb (D) and discard.

Maintain thermometers according to instructions in section 17.2.

2. Clean mounting plate (B). Use nonflammable instrument cleaning solvent to remove

stubborn dirt and corrosion.

3. Inspect the spinning or whirling mechanism (F and G) for wear. Chain links, swivels, and hooks are very susceptible to wear.

Repair or replace worn parts.

4. Tighten all screws.

5. Oil shaft or other spinning parts.

6. Replace thermometers, making sure

that they are securely mounted in holder.

7. Install a fresh wick following procedure

in section 17.1. Be sure wick is tied securely

to wet bulb.

Periodic l\/laintenance

1. Change the wick at least every 2 weeks

if instrument is used daily. If used irregularly,

change the wick at first sign of dirt or disFigure 17.6. — Sling psychrometers: A, Thermometer

retaining clip; B, mounting plate; C, dry-bulb thermometer; D, wet-bulb thermometer; E, wet-bulb

wick; F, sling chain; G, sling handle.

coloration. Pocket sling psychrometers often

require frequent wick changes because the instrument is usually slipped into a case immediately after each use and the wet wick

rubs against inside of case and thus becomes

discolored.

2. Always inspect spinning or whirling

mechanism for signs of wear before each use.

3. Store uncased psychrometers out of

direct sunlight and in a clean location. Damage to the thermometers is less likely if the instrument is hung up rather than laid down.

CROSS REFERENCE: Description 2.2;

Operation 11.1, 11.5.

100
CHAPTER 18

HYGROTHERMOGRAPHS

Because the hygrothermograph is a rather

deUcate instrument, the reUability of its data

depends to a large extent on the level of maintenance. Due to certain inherent characteristics of its sensors, large errors can occasionally

occur despite the best efforts of the observer.

These errors can be minimized, however,

through continuous general maintenance and

periodic calibration checks. Carefully service

hygrothermographs and recalibrate as necessary: (1) prior to each period of use, (2) after

changing the hair element, and (3) whenever

loss of caUbration occurs during use.

The following tools and supplies are required for efficient hygrothermograph maintenance: needle-nose pliers, small screwdriver,

small monkey wrench, camel's hair brush,

crocus cloth, and a clean wiping cloth.

Do not attempt temperature and relative

humidity calibration unless the hygrothermograph is in good mechanical condition. The

observer should be familiar with service requirements contained in the instrument's

manual. Additional copies of these manuals

are usually available from the manufacturer.

General maintenance items that apply to

most hygrothermographs are discussed below.

Refer to instrument manuals for details. Components of three popular hygrothermograph

models are shown in figures 18.1, 18.2, and

18.3. Reference letters used throughout this

chapter refer to figures 18.1, 18.2, and 18.3

unless otherwise specified.

18.1 CLEANING

Keep the instrument clean. Dirt and dust

can cause binding of the moving parts. Remove loose dust with a small camel's hair

brush. Brush lightly with instrument cleaning

solvent to remove hardened dirt. Do not oil

except as directed. Usually only the clock

need be oiled and this is best done by a clock

repairman. Avoid getting oil or solvent on the

hairs. If dusty, carefully brush hairs with soft,

clean camel's hair brush (fig. 12.4). Do not

use cleaning solvent on hairs. If extremely

dusty, wash the hairs with clean, mineral-free

water of air temperature, using a soft, clean

camel's hair brush. Replace hairs about every

2 years. Always keep in mind that hygrothermograph parts are delicate and are easily damaged by rough handling.

18.2 PEN ARM ASSEMBLIES

Allow just enough pen pressure on the recording chart to obtain a sharp and continuous trace. Pen pressure can be adjusted by

carefully bending the pen arm. The pens must

be sharp and clean. If the trace is too broad,

draw a piece of chart paper through the

points to clean out any dirt or congested ink.

If the pen is clogged with dried ink, remove

and wash in warm soapy water. Remove pen

by gently pulling it straight off the arm. Re101
Figure 18.1. — Bendix hygrothermograph. This hygrothermograph is of the clock-in-drum type. Components

are: A, Temperature pen arm;B, chart and chart drum; C, relative humidity pen arm; D, pen arm shifting rod

lever; E, temperature pen adjustment knob; F, Bourdon tube (temperature sensor); G, banjo spread hair

element (relative humidity sensor); H, relative humidity pen adjustment knob;/, magnification bar; J, swivel

hub and swivel hub setscrew; K, pivot pin; L, arbor or spindle; M, pen arm shifting rod; Af, arbor or spindle

(drive) gear; O, pinion shaft; P, pinion gear; Q, clock winding key; R, clock speed regulator.

Figure 18.2. — Belfort hygrothermograph. This clock

is mounted to the base in this instrument. Components are: A, Temperature pen arm; B, chart

and chart drum; C, relative humidity pen arm; D,

pen arm shifting rod lever; E, temperature pen adjustment knob; F, Bourdon tube (temperature

sensor); G, banjo spread hair element (relative

humidity sensor); H, relative humidity pen adjustment knob; /, magnification bar; K, arbor or

spindle; M, pen arm shifting rod; O, pinion shaft;

P, pinion gear; Q, clock winding key.

Figure 18.3. — Weather Measure hygrothermograph.

This hygrothermograph has a battery-operated

clock in the chart drum. Components are: A,

Temperature pen arm; B, chart and chart drum; C,

relative humidity pen arm; D, pen £irm shifting rod

lever; E, temperature pen adjustment knob; JF,

bimetal strip (temperature sensor); G, hair bundle

(relative humidity sensor); H, relative humidity

pen adjustment knob; M, pen arm shifting rod; S,

hooked magnification lever; T, upper hair jaw; U,

lower hair jaw.

102
place by sliding it back on the arm and gently

crimping shoulders with a pliers.

If, after cleaning, the pen still makes too

broad a trace, sharpen the pen point. Use a

point file or a fine mill file to sharpen the pen

point until light will not reflect off its nibs.

Do not make the pen too sharp or it will cut

the chart paper.

If pen fails to ink properly after cleaning

or sharpening, replace it with a new one.

After proper inking is insured, see if both

pens indicate the same time on the chart. If

not, adjust one of them by changing its position on the pen arm. Make sure pens are attached firmly enough so that they do not

slide out of position while in use.

18.3 CHART DRIVE ASSEMBLY

Remove all dirt and rust from spindle (L)

and gears. Lubrication of the spindle is often

recommended to prevent rust; however, too

much lubrication encourages the accumulation of dirt. It is often better instead to shine

the spindle with crocus cloth and minimize

the chance of dirt accumulation. Make sure

spindle is straight and that spindle and gears

are securely fastened.

Backlash can be a problem on some models

with clocks contained in the drum (fig. 18.1).

To check for backlash, lift pens from chart

and turn drum lightly back and forth. The

amount of play should cause an audible click

between the gears, but not enough to cause

more than 1/2 hour's backlash on a weekly

chart. Try this at several points around the

clock. If there is either no backlash or too

much backlash, adjustment is needed. Remove drum from the spindle and loosen the

three screws equally spaced on bottom of

drum (fig. 18.4). Shift gear away from center

of the drum, tighten the screws, and check

again for backlash. Continue this procedure

until, through trial and error, you obtain uniform backlash of an acceptable level.

The clock drive gear may mesh too tightly

with the large stationary gear (N) at bottom

of spindle (L) or inside chart drum (B), causing the clock to either stop or lose time. To

test for such a case, remove drum from spindle; if the clock then operates normally, the

gears are meshing too tightly. A bent spindle

can cause a backlash on one side of the clock

and a drag on the other side. Replace a bent

spindle.

If there is a drag between gears on clockin-drum models, remove drum from spindle

and very slightly loosen the three screws on

bottom of drum (fig. 18.4). Now, move pinion gear (P) away from center of drum. A

very slight movement will usually be

sufficient.

Tighten the screws, replace drum on

spindle, and test for amount of backlash.

18.4 CLOCK

Check clock by comparing rate of drum

revolution with chart time scale. If necessary,

use the regulator (R) provided to adjust clock

time. Move pointer of regulator towEird "S" if

clock is running fast, or toward "F" if it is

running slow. Have the clock overhauled by a

competent watch repairman if it does not respond to above regulation. It is good practice

Figure 18.4. — Loosen three screws on bottom of

drum and shift gear away from center of drum to

correct for backlash and drag between gears.

103

599-270 O - 76 - 8
to have the clock cleaned and adjusted by a

competent watch repairman annually. When

this is done, provide the repairman with the

instrument manual as it contains needed information on lubrication and timing specifications. If the instrument manual is not readily

available, the following information on clock

lubrication and timing requirements for the

two most common hygrothermographs will be

of value.

Bendix-Friez, Model 594 Series

Timing of the escapement. — 18,045 beats

per hour.

Mainspring lubrication. — Use a mixture of

one part oil, Elgin M-56A or Bendix-Friez oil

Part No. 502763, to three parts flake or

powdered graphite by volume.

Drive mechanism pivots. — These may be

lubricated with the oils listed above but without the graphite added.

Belfort, Catalog No. 5-594

Timing of the escapement. — Nine seconds

per hour (45 beats per hour) fast.

Mainspring lubrication. — Use Belfort Instrument Oil No. 5660 for warm weather

operation. For cold temperature operation

(0° and below), drain oil from mainspring barrel and relubricate with fine powdered graphite or molybdenum disulfide (molykote).

Mechanism gear train lubrication.— ¥ox

cold temperature operation use Belfort Instrument oil No. 5586.

18.5 CALIBRATION

Hygro thermo graph calibration consists

primarily of adjustments for zero and for

range or spread. Zero refers to the temperature and relative humidity indicated by the

position of the pens on the chart in relation

to the actual temperature and relative humidity of the surrounding air as measured

with wet- and dry-bulb thermometers. Range,

or spread, refers to the distance the pen arms

travel between maximum and minimum chart

values. Although instrument manuals contain

fairly complete information on hygrothermograph maintenance, they are usually quite deficient regarding calibration procedures.

18.6 ZERO ADJUSTMENT

Temperature Pen

Perform zero shift adjustment calibration

checks only when air temperature is holding

steady. Attempts to check calibration during

periods of changing temperature are usually

unprofitable due to the lag in reaction time of

the temperature-sensitive element.

Compare chart temperature indicated by

the pen to temperature indicated by a drybulb thermometer (unventilated), or a minimum thermometer (read top of alcohol

column). If chart temperature varies more

than 2° F. from thermometer reading, adjust

the pen accordingly. Adjust pen either up or

down by turning the knurled thumbscrew (E)

connected to the temperature element (F).

Briefly lift pen off the chart during adjustment to eliminate any effects of surface friction between pen and chart.

Relative Humidity Pen

The shifting of zero is a major source of

error for relative humidity data collected with

hygrothermographs. Depending on its direction, zero shift will result in recorded humidities that are either higher or lower than

those actually occurring. It is most likely to

accompany changes in weather. During range

or spread calibration, the hair element is

normally exposed to saturated air conditions

which results in a low zero position. Exposure

of the hairs to prolonged dry weather may

then cause an upward shift of the zero. Subsequent exposure to saturated air will often

result in a downward shift, often back to the

original calibration position. The tendency of

zero shift to be reversible suggests this source

of error could be minimized by periodic saturation of the hairs during extended periods of

continuous low humidities. In dry regions,

this might amount to exposing the hairs to a

saturated atmosphere for a few hours each

month (Middleton and Spilhaus 1953).

Make calibration checks while the relative

humidity is leveled off in order to minimize

the effects of lag in the response time of the

hair element. Do not attempt calibration at

low temperatures since the lag of the hair in104
creases greatly at temperatures below 20° F.

Base any adjustment of the relative humidity

pen on an average of three psychrometer readings obtained with an electric fan psychrometer (see section 11.2).

Adjust the zero if relative humidity indicated on the chart varies more than 3 or 4 percent from average of psychrometer readings.

Adjust the pen either up or down by turning

the knurled thumbscrew (H) connected to the

hair element (G). Briefly lift the pen off the

chart during adjustment to eliminate any effects of surface friction between pen and

chart.

18.7 RANGE ADJUSTMENT

Temperature Pen

Check the calibration and accuracy of the

temperature record for a given period by comparing maximum and minimum temperatures

on the chart with those obtained from standard maximum-minimum thermometers. If a

consistent difference of more than 2° F. is

found after satisfactory zero adjustment, recalibration is indicated. Recalibration for temperature range adjustment is rarely required

and unless specific instructions are provided

in the instrument manual, return to the manufacturer for this recalibration.

Relative Humidity Pen

When properly adjusted, the humidity pen

will register the same as the lowest afternoon

humidity obtained by using a psychrometer;

the humidity pen will also show a rise of between 95 and 100 percent at night if either

fog or dew is present.

Too great or too small a daily spread

(range) in a hygrothermograph humidity record is common. Like zero shift, range elongation is a major source of error for relative humidity data collected by hygrothermographs.

Range elongation apparently results from exposure to low humidities. Studies at Priest

River Experimental Forest in northern Idaho

show that range elongation may result from

exposure to minimum humidities no lower

than 30 percent. These studies also show that

the amount of elongation is related not only

to the degree of dryness but also to the length

of time that low humidities endure (Hayes

1942).

The only remedy for range elongation is to

make compensating range shortening adjustments. Conversely, a reduction in the range is

corrected by range elongation adjustments.

Several methods for making these adjustments

follow.

For sake of illustration, assume that the

adjustment for low humidity is correct and

saturated air is present at night. If the highest

humidity on the chart is over 100 percent, the

spread must be decreased. If the highest humidity on the chart is below 95 percent, the

spread must be increased.

Make the humidity spread adjustment only

at the time of day when the humidity pen on

the chart has leveled off at its lowest value for

an hour or more, preferably on a day when

humidity is below 30 percent.

1. Trial-and-error method. — {Refer to

figures 18.1, 18.2, and 18.3.) This method of

adjustment works best for field correction of

minor spread errors. It can be performed

without interrupting the weather record being

collected.

a. In the afternoons, after relative humidity has leveled off, make an average of three careful psychrometer

readings and determine relative humidity (see section 11.3).

b. Observe the difference between relative humidity determined by

psychrometer and the relative humidity indicated by the pen (C) on

the hygrothermograph chart.

c. Mark a pencil line on the magnification bar (I) at the swivel hub (J).

This will serve as a reference if you

want to start over.

d. Loosen swivel hub setscrew (J) that

holds magnification bar (I) in place

(fig. 18.5).

e. Move magnification bar (I) far

enough to change pen setting on

chart about one-half the difference

in relative humidity observed in step b.

Move magnification bar (I) out away

from chart drum (B) to decrease

spread.

105
Figure 18.5. — Adjusting the magnification bar on a

Belfort hygrothermograph.

Figure 18.6. — After saturating hair element with a

soft camel's hair brush, the humidity pen should

indicate between 91 and 95 percent relative humidity.

Move bar (I) in toward chart drum

(B) to increase spread.

A movement of 1/8 inch will cause a

change in spread of several percent.

f. Tighten the swivel hub setscrew (J)

firmly.

g. Since the zero adjustment has now

been altered, adjust pen with thumbscrew (H) to correspond with actual

psychrometric humidity.

On hygrothermographs of the type shown

in figure 18.3, the function of the magnification bar is performed by a hooked magnification lever (S) through which the hair bundle

passes. Rotate this lever to the right to increase magnification and to the left to decrease magnification.

On another type of hygrothermograph, the

magnification bar (I) is suspended at the right

end instead of at its center. It is not adjustable, but a suspension slide that holds the

hairs can be moved along the magnification

bar. Move the suspension slide out away from

the clock to increase the spread. Move the

slide in toward the clock to decrease the

spread. Note that the movement is opposite

from that for the hygrothermographs shown

in figures 18.1 and 18.2.

Often, several adjustments over a period of

a week or two are required before the proper

calibration is obtained by using this trial-anderror method of range adjustment.

2. Hair-wetting method. — This is a more

precise, time-consuming method. Good results

can be obtained in about 2 hours; however,

followup with the trial-and-error method is

recommended. The wetting method is especially helpful after installing a new set of hairs.

a. Perform this method either outside

on a warm, dry afternoon, or inside a

warm, dry room.

b. Take three very careful psychrometric readings to determine the correct

humidity; set the humidity pen accordingly.

c. Dip a soft camel's hair brush in clean

water. Stroke the humidity hairs upward on both sides until they are immersed in a continuous stream of

water (fig. 18.6). Hold the water

container directly beneath the hairs.

Continue this procedure until the

hairs are completely saturated. Then

stroke all the free water off the hairs,

allowing them to spread apart.

d. Immediately after hairs are spread

apart, read the humidity on the

chart. If the humidity pen is approximately 93 percent, do not change

the adjustment.

106
If the pen indicates over 95 percent,

the spread is too great.

If the pen indicates under 91 percent, the spread is too small.

Usually the hairs will indicate approximately 93 percent when saturated with water

and 100 percent when saturated with vapor

(fog, dew).

e. If adjustment is necessary, follow instructions for moving the magnification bar (I) or hooked magnification

lever (S) as outlined in the trial-anderror method.

f. After magnification adjustment has

been made, wet the hairs again.

g. Set humidity pen at 93 percent using

thumbscrew (H) adjustment.

h. Let instrument sit for at least 30

minutes to permit humidity pen to

return to and level off at its former

low value. Then set pen according to

a new psychrometric humidity

reading.

i. Continue to repeat the process until

the pen, when wet, will indicate approximately 93 percent, and when

dry will indicate the current low humidity as measured by the psychrometer.

Occasionally, a set of hairs will indicate

only 80 percent or so when wet with water.

but 100 percent when wet with night fog or

dew. If this occurs, order and install a new set

of hairs. After 3 or 4 days' exposure, proceed

with the adjustment process.

3. Wet-towel method. — This is the same

as the hair-wetting method explained above

except the 100 percent point is obtained by

surrounding the instrument with wet towels,

or by placing it in a box lined with wet towels. If this method is used, the towels should

be left until the arm reaches its highest point

(approximately 10 minutes) which will be

100 percent relative humidity.

4. Humidity-chamber method. —This

method (Thornthwaite 1939) involves producing and maintaining a series of different

relative humidities within a metal-lined, airtight chamber by means of saturated inorganic salt solutions (table 18.1).

The calibration chamber must be equipped

with a fan to insure complete air circulation.

The salts should be spread in a shallow pan

and distilled water added to produce a thick

solution that has an abundance of undissolved

material remaining. Refer to Thornthwaite

(1939) for additional details regarding this

method. The corrosive nature of the salt solutions involved should be considered when

using this method of calibration.

CROSS REFERENCE: Description 2.3; Installation and Exposure 8.4; Operation 12.

Table 18.1. —Relative humidities maintained at specified temperatures

by various saturated saline solutions

Relative humidity obtained using saturated solutions of:

Temperature KNO3 NaCl Mg(N03 h • 6H2O MgClj-GHjO LiCl

Percent

104 90 76 51 33 16

95 92 75 51 33 16

86 94 75 52 33 16

77 95 75 52 32 16

68 95 75 53 32 16

59 95 76 53 31 16

50 95 76 53 31 16

41 96 76 54 30 16

32 96 76 54 30 16

107
CHAPTER 19

ANEMOMETERS

Anemometers are relatively sturdy instruments and can provide many years of

trouble-free operation if given reasonable handling and regular maintenance. For most anemometers, maintenance consists of an annual

check and monthly or periodic lubrication

while in use. During the annual check, the instrument should be disassembled, cleaned,

lubricated, and inspected for proper calibration and mechanical soundness.

clean them. Badly burned or pitted contact

points are often the result of too strong an

electrical current.

When available, compressed air may be

used to good advantage in cleaning out the

anemometer housing or removing dirt from

around the gears as well as from other hard to

reach places.

19.2 LUBRICATION

19.1 CLEANING

All anemometer parts, except the electrical

contact unit, may be cleaned with a nonflammable instrument cleaning solvent such as

methyl ethyl ketone. Several commercial

preparations of this and other acceptable solvents are available under a variety of brand

names (MEK, VARSAL, etc.). Do not use

preparations containing carbon tetrachloride;

it can cause rust, but more importantly, its

fumes are poisonous. Similarly, do not use

gasoline or other highly flammable liquids.

Pipe cleaners and small toothbrushes are

handy for applying solvent and removing

gummed oil or stubborn dirt from anemometer parts.

Electrical contacts should be cleaned first

with crocus cloth and then by drawing a clean

piece of hard-finish paper between them. Replace the contacts if they are badly pitted or

so dirty that a file or emery cloth is needed to

Depending on the type of anemometer,

either anemometer oil or special silicone type

lubricants are specified for lubrication. These

lubricants are usually available from the anemometer manufacturer. Anemometer oil is

simply a light, nongumming instrument oil;

thus, any similar light instrument oil can be

used. Sewing machine oil and cream separator

oil are often recommended as substitutes for

anemometer oil. When using substitutes for

anemometer oil, use ones that will not impair

anemometer operation at low temperatures.

Anemometers should be lubricated carefully

and sparingly. Wipe off excess oil immediately. Most anemometers require only one or

two drops of oil at any one spot. Consider a

drop as the amount of oil that will collect at

the end of a piece of fine wire (about the size

used for paper clips). Such a wire makes a

handy applicator. Merely dip the end of the

wire into the oil, let the excess run off, and

then apply the amount remaining on the end

of the wire to the part requiring lubrication.

108
19.3 MECHANICAL INSPECTION

AND RECALIBRATION

Many mechanical deficiencies can be identified by merely spinning the cups and observing their action. You should be able to start

the cups spinning by blowing into them. Similiirly, the cups should never come to an

abrupt stop, even at very low speeds. Hard

starting and abrupt stopping may indicate

need for oil, need for cleaning, bent or worn

parts, or improper assembly. In normal operation, cups should not wobble while spinning.

Wobbling often indicates a bent shaft.

Although periodic anemometer calibration

checks and necessary recalibrations are critical

factors in anemometer peformance, they are

often overlooked or purposely avoided. This

situation is usually due to the lack of necessary instrumentation or the high cost of having the job done at the factory.

A portable calibrator (fig. 19.1) has recently been developed (Ryan 1970) which allows

Figure 19.1. — Anemometer

calibration: Upper, Overall

view; lower left, anemometer

housing installed for calibration; lower right, top view

showing anemometer cups

installed for calibration.

109
fairly accurate recalibration of anemometers.

The unit can be constructed for less than a

hundred dollars thereby being within the

means of most fire control agency budgets.

The recalibration process takes less than 1

hour per anemometer. Ryan reports finding

initial calibration errors as high as 28 percent

using this instrument.

19.4 CIRCUIT CHECK

A major item when inspecting anemometers for mechanical soundness is to check for

a flow of current from the anemometers to

the readout device. Check by testing the

switch contacts with a continuity tester or attach a wind counter, turn the cups by hand,

and record the number of cup revolutions required to advance the counter one count.

Now check to see if the anemometer consistently advances the counter one count each

time the proper number of cup revolutions

occurs.

If the counter or other readout device fails

to respond properly, the trouble may be in

the wires or connecting cable. Before attempting to check the wiring, however, it is wise to

first doublecheck the contact mechanism. If

the anemometer is of the multiple contact

type the trouble may be that one or more of

the pins on the contact wheel are worn short

and consequently not closing the contact as

they travel past it.

To check for a broken wire in either the

anemometer or the readout device, first disconnect the suspected wire. Attach a lead

from the continuity tester to one end of the

wire and attach the second lead to the other

end of the wire to be tested (fig. 19.2). If the

arrow on the dial of the continuity tester does

not move off the zero position, a break in the

wire is indicated.

To check for a short in a multiple conductor cable, first disconnect the cable from the

instrument and its readout device. Attach one

lead from the continuity tester to the end of

one of the wires in the cable. Now touch the

other lead from the tester to each of the other

wire ends, one at a time. A short is indicated

when the arrow on the dial of the tester

moves off the zero position. Check each wire

in the cable against all the other wires in the

same manner.

Detailed maintenance instructions for the

Figure 19.2. — Using a continuity tester to check an anemometer circuit.

110
N P.

types of anemometers likely to be used at

fire-weather stations follow. While these instructions are designed to be used cookbook

fashion during actual maintenance, we recommend they be first read all the way through

before starting disassembly.

19.5 SMALL AIRWAYS TYPE

ANEMOMETER

(Friez, Bendix-Friez, and the Instruments Corporation Models)

Refer to figure 19.3.

Monthly Maintenance

Remove front inspection plate (D) and

check the spindle (F), top bearings (J), and

the worm gear (H). If they need oil, add one

to two drops each on the top bearing, the

worm gear, and the bottom tip of the spindle.

Apply oil carefully and wipe off any excess

before replacing inspection plate.

Annual Maintenance

Disassembly

1. Unscrew cap nut (A) and lift off the

cups (B) and rain shield (C).

2. Remove front cover plate (D).

3. Loosen set screw (0) above cover plate

and lift out the spindle (F).

4. Remove back cover plate (Q) and disconnect wire from contact unit (G) by loosening screw (R) at the binding post (N).

Cleaning and Lubrication

5. Wash spindle, gears, and other parts

(but notthe contact unit (G)) with instrument

cleaning solvent (see section 19.1).

6. Drain and allow to dry.

7. Check contact points (S). If badly

pitted, replace. If dirty, clean contact points

with crocus cloth and then pull a piece of

hard-finish paper between them.

8. Check to make sure positive, but not

hard, contact is made when worm wheel pin

(I) closes the contact points (S). Bent contact

fingers (T) can cause hard contact. To correct

this situation, use needle-nose pliers and carefully straighten the contact fingers.

9. Replace spindle and tighten set screw

(O).

mfiäMmtf:»m,.ri ^I^JÊLMummL^.:&:è..

Figure 19.3.— Small Airways type anemometer: A,

Cap nut; B, cups; C, rain shield; D, front cover

plate; E, housing; F, spindle with worm gear; G,

contact assembly; H, worm gear; I, worm wheel; J,

upper ball bearing; K, lower bearing adjustment

screw; L, thumb clamp screw; M, grounded terminal; N, insulated terminal; O, spindle retaining

screw; P, mounting sleeve; Q, back cover plate; Ä,

binding post screw; S, contact points; T, contact

fingers.

Ill
10. Apply one drop of anemometer oil

(see section 19.2):

a. At each end of the worm wheel shaft

(I)

b. At top of gear on the spindle (F).

c. At lower end of the spindle (F).

d. On lower bearing (K).

e. On upper ball bearings (J).

11. Immediately wipe off any excess oil

that may have run onto parts not requiring

lubrication.

Mechanical Inspection

12. Spin the spindle to be sure that it

turns easily. If it does not coast freely, turn

lower bearing adjustment screw (K). This

screw can be reached by inserting a screwdriver through the bottom of the instrument.

Using the adjustment screw, raise or lower the

spindle just enough to get the longest spin.

13. Reconnect wire from contact unit to

the screw (R) at the binding post (N).

14. Replace washer, rain shield, cups, and

cap nut. Spin cups and check to see that the

instrument is operating properly (see sections

19.3 and 19.4).

Reassembly

15. Replace front and back covers. Tighten screws firmly but be careful not to strip

threads.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.6 FORESTER NO. 9X140

ANEMOMETER

Refer to figure 19.4.

Monthly Maintenance

This instrument requires complete lubrication at least once for every 3 months of uninterrupted use. In order to accomplish this, the instrument has to be taken from the pole, disassembled (items 1-4, below), lubricated (items

8-10, below), and reassembled (items 14-18,

below).

Annual Maintenance

Disassembly

1. Unscrew cap nut (A) and remove cups

(B).

2. Remove cylinder shell screw (D) on side

of cylinder head (C). Use a twisting movement

to remove cylinder head and stud (C).

3. Unscrew the slotted screw (H) at top of

main shaft (F) which seals the oil channel to

the lower bearing. (A few early models have a

lockring instead of a screw at this point.)

4. Remove main shaft (F) through bottom

of cylinder shell (E). If it sticks, lightly tap the

top of the main shaft.

Oeaning and Lubrication

5. Do not attempt to wash the shielded

bearings (E). These operate at 0.0001-inch

Figure 19.4. — Forester 9X140 anemometer: A, Cap

nut; B, cups; C, cylinder head and stud assembly;

D, cylinder shell screw; E, cylinder shell with internal gear; F, main shaft; G, sprocket gear assembly; H, main shaft oil channel screw; /, sprocket gear; J, contacts; K, balance disc; L, sprocket

gear striking pen.

112
clearance and cleaning solvents may do more

harm than good.

6. Clean all other parts, as needed, using an

instrument cleaning solvent (see section 19.1).

7. Check the silver contact points (J) and

replace if badly burned or pitted. If dirty, clean

with crocus cloth and then by pulling a piece of

hard-finish paper between them.

8. Place two drops of anemometer oil on

the shield of each bearing (see section 19.2).

9. Place one drop of anemometer oil on

sprocket gear shaft (I).

10. Place two drops of oil at top ofinternal

gear located inside the cylindershell (E).

11. Immediately wipe off any excess oil

that may have run onto parts not requiring

lubrication.

12. Check the contact mechanism (J) by rotating the sprocket gear (I) and observe whether the striking pin (L) causes the bronze fingers

(J) to make and break contact. The movement

of the inside contact point should be between

1/32 and 1/16 of an inch. The outer contact

point should deflect about 1/64 of an inch.

13. Check to see that the screws holding the

contact arms are tight and secure.

Reassembly

14. Insert main shaft (F) into bottom of

cylinder shell (E) and up through the two

bearings.

15. Install the oil channel screw (H) (or

lockring) at top ofshaft.

16. Using a twisting motion, push on the

cylinder head (C), line up the hole in the side,

and tighten the screw (D).

17. Replace the balance disc (K) being careful to keep the side marked "top" on top.

18. Replace cups Eind tighten the cap nut.

19. Spin cups and check instrument for

proper operation (sections 19.3 and 19.4).

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.7 FORESTER MODEL 9X150

Refer to figure 19.5.

Monthly Maintenance

This instrument does not require monthly

maintenance if proper annual maintenance is

provided.

Annual Maintenance

Disassembly

1. Remove 1/8-inch pipe plug from side of

the body and drain the versilube fluid from the

instrument. NOTE: Versilube is a special

synthetic lubricant which will neither congeal

nor impair operation at subzero temperatures.

A bottle of this fluid is supplied with each instrument and additional quantities can be ordered from the manufacturer. DO NOT USE

ANY OTHER LUBRICANT.

Figure 19.5. — Forester Model 9X150 anemometer

(upper) assembled view, (lower) unassembled

view: A, Cap nut; B, washer; C, cups; D, housing;

E, upper main shaft; F, exterior terminal posts;

G, rotor cap; H, balance disc; /, balance weight;

J, rotor hub pin.

113
2. Unscrew 1/4-inch stainless steel cap nut

(A) and washer (B) on top of cups. Remove

cups (C), balance disc (H), and rain shield (G).

Do not disturb the small weight (I) on the balance disc.

Qeaning and Lubrication

3. Clean dust and oil residue from exterior

of housing (D), cups, interior of the rain shield,

and the brass surfaces of the terminal posts (F).

4. Briefly turn anemometer upside down.

The versilube fluid remaining in the body will

lightly lubricate lower main shaft bearing.

5. Turn anemometer upright and add

three drops of versilube on the upper main

shaft bearing.

6. With anemometer in the upright position, refill the body with fresh versilube fluid.

Fill to lower edge of the fill hold.

Reassembly

7. Replace pipe plug, using Teflon pipe

thread tape.

8. Replace the rain shield and the balance

disc. Replace the cups making sure that the pin

(J) on the hub is seated in the holes on the

balance disc and rain shield. Replace the washer

and the cap nut.

Mechanical Inspection

9. Spin shaft and check for iiny binding

action. If binding occurs, check for improper

assembly, bent or worn parts, dirt, and need for

oil.

10. Use a continuity tester and check

switch contacts. Every 15 turns of the cups

should make one contact (see section 19.4).

11. If the anemometer does not appear to

operate properly, return it to the manufacturer. Do not disassemble any further than indicated above as the mercury switch inside the

housing is easily broken.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.8 CHISHOLM MODEL 2B3C

ANEMOMETER

Refer to figure 19.6.

Monthly Maintenance

Remove cap nut, screw, or bolt from top of

cups. Place one to three drops of oil in the oil

duct which is exposed when the cap nut, screw,

or bolt is removed.

Annual Maintenance

Disassembly

1. Unscrew cap nut (A) and lift off the

cups (B).

2. Remove mounting nut lockring (N) and

slide mounting nut (O) from main shaft (D).

3. Remove the small bolt that goes

Figure 19.6. — Chisholm Model 2B3C anemometer: A, Cap nut; B, cups; C, electrical unit retaining bolt; D,

main shaft; E, electrical unit mounting point; F, electrical unit; G, cylinder retaining screw; H, revolving

cylinder; /, cylinder head; J, roller bearings; K, sprocket gear; L, contact fingers; M, contact points; N,

mounting nut lockring; O, mounting nut.

114
through the main shaft (D) at point (E).

4. Carefully slide the electrical contact

unit (F) down over the end of the main shaft

(D).

5. Remove the small screw (G) from the

revolving cylinder (H). Hold the revolving cylinder with one hand and remove the cylinder

head (I) by turning it to the left with the other

hand.

6. Remove the main shaft (D) from the

cylinder head (I).

Qeaning and Lubrication

7. Do not attempt to wash the electrical

contact unit (F).

8. Wash all other parts in an instrument

cleaning solvent (see section 19.1).

9. Put two drops of anemometer oil

around the top of the two roller bearings (J) of

the main shaft (see section 19.2).

10. Put two drops of anemometer oil

around the worm gear located inside the top of

the revolving cylinder (H).

11. Immediately wipe off any excess oil

that may have run onto parts not requiring

lubrication.

Mechanical Inspection

12. Check the contact mechanism by slipping the entire electrical contact unit on the

shaft and temporarily fastening it into place.

Manually turn the sprocket gear (K) and see if

the striking pin causes the bronze fingers (L) to

make and break contact at the silver contacts

(M). Remove the contact unit from the shaft.

Reassembly

13. Place cylinder head (I) on top of the

roller bearings (J). Put the revolving cylinder

(H) up over the shaft (D) atnd on the cylinder

head (I). Turn it to the right to match up the

holes. Replace the small screw (G).

14. Turn anemometer upside down and rotate the revolving cylinder until the small pin

on the gear wheel (K) is face up and in line with

the shaft. Carefully slide the electrical contact

unit up over the shaft and into the revolving

cylinder. At this point, the contact points

should be to the left ofthe medn shaft when the

anemometer is pointing away from you.

15. Replace the small bolt (C) through the

electrical unit and shaft.

16. Replace cups and tighten cap nut.

17. Spin cups and check to see that the anemometer is operating properly (see sections

19.3 and 19.4).

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.9 STEWART ALUMINUM CUP

ANEMOMETER

Refer to figure 19.7.

Monthly Maintenance

According to manufacturer's instructions,

this instrument does not require monthly service unless electrical contact points need adjustment (see item 8, below).

Annual Maintenance

Disassembly

1. Loosen set screw on side of the hub and

lift off cups.

2. Loosen screws and remove cover plate

from the housing (A).

3. Do not remove the nylon pinion gear

(F) or loosen the brass bearing blocks (C) at the

ends of the shaft. If you do, tiny ball bearings

will fall out. These are extremely difficult to

replace.

Cleaning and Lubrication

4. Using a clean, soft cloth, wipe off the

top of the spindle (B), the spindle sleeve, and

the inside of the hub. Lightly oil each of these

areas with silicone fluid lubricant.

5. Place several drops of silicone fluid on

the spindle just above the top bearing and just

above the lower bearing. Now spin the spindle

clockwise to work the lubricant into the

bearings.

6. Put a small amount of silicone grease

(or vaseline) on the gear pinion (F) where the

ground strap is attached.

Mechanical Inspection

7. Spin shaft and check for friction or

binding. If it binds, check for improper assembly, bent or worn parts, dirt, and need for oil.

8. Check the action of the contact leaf

spring (D). If necessary, adjust the spring contact so it is just barely moved by the pin on the

ring gear. If too tight, excessive wear will result

115
Figure 19.7. — Stewart aluminum cup anemometer:

A, Housing; B, spindle; C, bearing block; D, contact leaf spring; E, lower thrust bearing; F, pinion

gear.

and the anemometer will stick at low windspeeds; if too loose, the attached readout

device may not indicate properly.

Reassembly

9. Replace cups and tighten setscrew.

10. Replace cover plate.

11. Spin cups and check to see that the anemometer is operating properly (see sections

19.3 and 19.4).

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.10 STEWART 4-CUP

ANEMOMETER

(Models prior to 1959; with black

cups)

Refer to figure 19.8.

Monthly Maintenance

Remove the inspection plate (A) and check

the top and the bottom of the spindle (C). If

dry, add one to two drops of oil at each of these

locations. Some models contain an oil duct on

top of the rotor for lubrication of the top of the

spindle. This duct often becomes plugged up

and may require cleaning. If duct is lacking,

remove cups and apply oil to the top of the

spindle. Apply oil carefully and wipe off any

excess before replacing the inspection plate.

Annual Maintenance

Disassembly

1. Remove screw on the top of cup assembly hub and remove cups. If there is no screw

on top, loosen set screw in the side of hub and

slip cups off the hub. If cups will not slip off

after removing setscrew, hold the anemometer

shaft with one hand and use the other hand to

unscrew cups.

2. Remove the cover plate (A).

3. Always keep the housing (B) in an upright position. If turned upside down, four

small ball bearings will fall out.

4. Unscrew bushing shaft from housing

and slide over spindle (C). Remove spindle carefully. Ifit offers resistance, move it from side to

side until it lifts out.

5. Do not remove pinion gear (E) or

loosen the brass bearing block at end ofshaft. If

you do, the tiny ball bearings contained with116
Figure 19.8. — Stewart 4-cup anemometer: A, Cover

plate; B, housing; C, shaft; D, worm gear; E, pinion

gear; F, contact points; G, lower thrust bearing; H,

contact leaf spring.

in might fall out. They are extremely difficult

to replace.

Qeaning and Lubrication

6. Wash the gears, shaft, spindle, and other

parts in instrument cleaning solvent (see

section 19.1). Flush the entire housing with

solvent.

7. Insert the spindle temporarily and work

it around and up and down.

8. Drain solvent from housing and set

aside until dry.

9. Put two drops of anemometer oil on the

gears (see section 19.2).

10. Put two drops of anemometer oil at the

top of the shaft (through the hole in the top of

the hub, if present) to lubricate the upper

bushing.

11. Immediately wipe off any excess oil.

Mechanical Inspection

12. Replace gears, spindle, and shaft. Replace cups and tighten setscrew. Spin cups

slowly and check for friction or binding (see

sections 19.3 and 19.4).

13. Check the action of the contact leaf

spring (H). If necessary, adjust the spring contact so that it is just barely moved by the pin on

the pinion gear (E). If too tight, excessive wear

will result and the anemometer will stick at low

airspeeds; if too loose, the attached readout

device may not indicate properly.

14. If unable to correct mechanical difficulties by cleaning, oiling, or adjustment, the instrument should be replaced by a newer model

anemometer.

Reassembly

15. Replace the gasket. If the gasket is similar to the one in figure 19.8, put the cutout

portion up so the pinion gear (E) will not bind

on it.

16. Replace cover plate.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.11 BELFORT TOTALIZING

ANEMOMETER

Refer to figure 19.9

Monthly Maintenance

Maintenance should be performed at least

every 3 months, more often if anemometer is

117
-^

i>.. r^'

7

Figure 19.9. — Belfort totalizing anemometer: A, Cap

nut; B, hub screw; C, cups; D, housing; E, back

cover plate; F, spindle retaining screw; G, spindle;

H, upper ball bearings; /, worm gear; J, worm

wheel with pins; K, terminal block assembly; L,

thumbscrew.

constantly exposed to excessive dust, frequent

rains, or strong continuous windspeeds. This

periodic maintenance should be the same as

outUned below for annual maintenance.

Annual Maintenance

Disassembly

1. Remove the cap nut (A), loosen setscrew (B) in the hub of cup assembly, and remove the cups (C).

2. Release spindle retainer screw (F) located in the housing (D) and lift spindle (G)

straight up out of housing.

3. Remove front and rear (E) cover plates.

Qeaning and Lubrication

4. Wash the spindle and upper ball bearing

(H) in an instrument cleaning solvent (see section 19.1).

5. Inspect counter mechanism. If very

dirty, wash and oil the lower ball bearing and

wipe off all dirt and oil from the mechanism as

well as from the interior of the housing.

6. Apply one drop of anemometer oil or

other light, nongumming instrument oil, such

as the Belfort Instrument Co. # 5600, to each

ofthe following points:

a. The upper ball bearings (H).

b. The spindle (G).

c. The worm, lower spindle bearing as-.

sembly (I).

d. The worm assembly (J).

e. The contact operating pins — but not

on the contacts themselves. Do not

apply too much oil — use only a few

drops for the entire lubrication procedure (see section 19.2).

Mechanical Inspection

7. Inspect contacts. Clean with crocus

cloth and pull a piece of hard-finish paper between them. If contacts are burned or pitted,

replace them and check for overloading.

8. Replace counter and contact mechanism.

9. Replace the spindle and tighten the

spindle retainer screw. Check to see that contacts and worm wheel are operating properly.

Reassembly

10. Replace the cups on the spindle.

Tighten the setscrew in the hub of the rotor

assembly just enough to prevent the spindle

from turning while the cap nut is being put in

place and tightened snugly. After the cap nut is

installed, finish tightening the setscrew.

11. Spin the cups by hand to see that they

turn freely. If not, check for improper assembly, bent or worn parts, dirt, and need for oil

(see sections 19.3 and 19.4).

12. Replace and cover plates.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1,

13.2.

118
Figure 19.10. — Priez dial type anemometer: A, Oil cup-cap nut; B, rotor hub set screw; C, cups; D, top

bushing; E, spindle with worm; F, dial cover plate; G, housing;//, gears;/, 1/60-mile contact; J, contact adjustment screw; K, 1-mile contact; L, thumbscrew clamp; M, grounded terminal; N, 1/60-mile terminal; O,

1-mile terminal; P, oil point plug; Q, outer dial wheel; R, inner dial wheel; S, 1-mile contact pin; T, dial screw;

U, location of 10-mile bar.

19.12 FRIEZ DIAL TYPE

ANEMOMETER

Refer to figure 19.10.

Monthly Maintenance

Remove plug (P) from backside of housing

(G) (side opposite dial). Put one drop of oil at

the top of the worm gear (Q) on the spindle (E).

Put one drop of oil at the lower end of the

spindle where it enters the lower bearing.

Unscrew top from oil cup (A) at top of anemometer. Check to see that wicking extends

down the center pipe. Fill cup about half full of

oil.

Annual Maintenance

Disassembly

1. Unscrew brass oil cup and cap nut (A).

2. Loosen setscrew (B) and remove cups

(C).

119

599-270 O - 76 - 9
3. Unscrew top bushing (D) and lift

spindle (E) from housing (G).

4. Remove cover plate (F) on dials by removing the two holding screws. Leave dials in

place.

Cleaning

5. Clean spindle (E) and top bushing (D)

with instrument cleaning solvent (see section

19.1).

6. Blow out oil duct in top of spindle to

clear it of all obstructions from the top to the

small hole in the side of the spindle atthe level

of the top bushing.

7. Inspect contact points. If either the

1/60-mile contact (I) or the mile contact (K)

are dirty, clean with crocus cloth and then pull

a piece of hard-finish paper between them.

Mechanical Inspection

8. If the 1/60-mile contacts do not open

sufficiently, increase the clearance by turning

the contact adjustment screw (J) to the left. If

the contact closure is insufficient, turn the

contact adjustment screw to the right.

9. If the 1-mile contacts do not open

enough, loosen the screw that holds the lower

portion of the contact and drop the contact

down slightly. If they do not close sufficiently,

lift the contact up slightly.

10. It may be necessary to bend the spring

section of each of these contacts to secure

proper operation but this should be a last

resort.

Reassembly

11. Return the spindle, making sure it is

seated in the bottom bearing. Replace top

bushing.

12. Replace cups and tighten setscrew.

Lubrication

13. Put one drop of anemometer oil on

each gear wheel on the front of the dial. Replace glass dial cover and tighten holding screws

(see section 19.2).

14. Remove plug (P) from housing on back

of dial. Put one drop of anemometer oil at the

top of the worm gear on the spindle. Put one

drop of oil at the lower end of the spindle

where it enters the lower bearing. Replace plug.

15. Unscrew cover from brass oil cup. If

wick is absent, one can be made from heavy

cotton sewing thread. It should lead from the

oil cup down to the oil duct. Fill oil cup with

anemometer oil to level of spindle.

16. Replace oil cup on top of spindle and

check hole in spindle to be sure that oil is flowing onto the bushing.

17. Spin cups by hand and check to see that

anemometer is operating properly (see sections

19.3 and 19.4).

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1,

13.2.

19.13 WEATHER MEASURE W164

AND W164B CONTACT

ANEMOMETER

Refer to figure 19.11.

Monthly Maintenance

Routine monthly service is not required for

this instrument if annual maintenance is performed as specified below.

Annual Maintenance

Disassembly

1. If Model W164B, remove its mechanical

counter by removing the counter face plate and

the fastener in the back of the counter. To free

the counter from the housing, simply press the

entire assembly forward. Model W164 does not

have a mechanical counter.

2. Remove the cups (A) by unscrewing the

lock nut (B) and cap nut (C) at the top of the

shaft (H) and pushing upward gently atthe base

of the shaft.

3. Remove the bearing setscrew (D) on

the side of the housing (I). Now remove the

bearing oil seal (E) atthe top of the shaft (H) by

turning upward and off the base assembly.

Remove the top bearing (F).

4. Loosen the top housing lock pin (K)

and turn the top assembly upward and off the

bottom housing (L).

5. To disassemble further, remove the bottom gear plate from the bottom support assembly by lifting it upward and off the guide pin.

6. Care must be taken to maintain the

proper shaft bearing clearance during assembly.

To assure the correct clearance, scribe indica120
Figure 19.11.—Weather Measure W164 contact

anemometer: A, Cups;B, cap lock nut; C, cap nut;

D, top lock screw; E, bearing oil seal; F, top bearing; G, bearing oil seal; H, drive shaft with worms;

/, top housing; J, drive gear; K, top housing lock

pin; L, bottom housing; M, cannon plug; N,

weather boat.

ting marks on the bottom bearing support and

base-plate assembly prior to disassembly.

7. To remove the shaft (H), loosen the

bottom bearing by screwing it down until sufficient clearance is accomplished to slip the shaft

off the worm and out of the bottom assembly.

Cleaning and Lubrication

8. Lubricate the bottom and the top bearing with anemometer oil that preferably has a

silicone base. Use a dry film lubrication on the

gears (see section 19.2).

Mechanical Inspection

9. Check the contacts. Replace them if

they are pitted or burned and check for overload or inadequate spark suppression.

Reassembly

10. Replace shaft, being careful to maintain

the proper shaft bearing clearance.

11. Return the bottom gear plate to the

bottom support assembly.

12. Screw the top assembly on to the bottom housing. Tighten the top housing set

screw.

13. Replace the top bearing and the bearing

oil seal. Tighten bearing setscrew.

14. Replace cups and screw down the cap

nut and then the cap lock nut.

15. Spin cups and test operation (see sections 19.3 and 19.4).

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.5; Operation 13.1.

19.14 DWYER WIND METER

Refer to figure 19.12.

Maintenance requirements for this instrument are relatively simple. It must be kept

clean, dry, and static free.

Cleaning

1. Clean the outer shell (A) with a damp

cloth. Do not use cleaning agents that attack

plastic.

2. Clean inner tube (B) by using either the

treated pipe cleaners provided with the instrument or regular pipe cleaners (fig. 19.13). Before cleaning inner tube, unscrew the metal

plug (D) on the bottom and remove the white

121
Figure 19.12. — Dwyer hand-held wind meter: A,

Outer shell; B, inner tube; C, indicator ball; D, bottom plug; E, top stem.

ball (C). After cleaning, replace ball and metal

plug.

Do not press on the white indicator ball with

fingers or other objects as it is easily deformed

and damaged, rendering it unusable or

unreliable.

Drying

If moisture enters the inner tube, unscrew

bottom plug and remove white ball. Clean tube

with a pipe cleaner (fig. 19.13). After all moisture has been removed, replace ball and return

metal plug.

Removing Static

A static electricity charge may cause the ball

to stick in the tube. This can be corrected by

running a pipe cleaner up and down in the tube

(fig. 19.13). Follow procedure as in cleaning or

drying the tube.

Calibration

Proper calibration depends on the instrument being maintained in a clean, dry, and

Figure 19.13. — Top, Cleaning, drying, and removing

static from inner tube; bottom, cleaning top stem

pinhole.

static-free condition. Be sure to keep the tiny

pinhole in the top stem (E) clean and open. Use

nylon bristles provided with the meter to accomplish this task (fig. 19.13). Do not use wire,

pins, drills, etc., which might accidentally enlarge the opening.

CROSS REFERENCE: Description 3.1;

Operation 13.4.

122
CHAPTER 20

WIND COUNTERS

Maintenance requirements for wind counters are mainly concerned with the electrical

circuit. Items such as maintaining sufficient

battery strength; clean, tight electrical connections; and sound wiring are critical to continuous trouble-free operation.

20.1 BUZZERS AND FLASHERS

1. Install fresh batteries whenever the buzz

or flash becomes weak.

2. At least once a year, clean buzzer contacts with crocus cloth and hard-finish paper.

3. Periodically check electrical connections

for tightness. Remove corrosion as it

accumulates.

4. If buzzer fails to operate, or operates

weakly or intermittently, follow this procedure

successively until the trouble is corrected:

a. Replace batteries. Make sure thatthey

are hooked in series rather than parallel (fig. 20.1).

b. Replace lamp or flasher.

c. Check the buzzer contacts. Burned

contacts indicate too much current.

Usually two to four lV2-volt dry

cells are enough; the number depends

on the hne distance, buzzer voltage,

and battery strength.

d. Check all electrical connections on

buzzer. Snap off the cover and check

the inside connections.

e. Using a rubber handle screwdriver,

short across from switch to buzzer. If there is no response, clean the

buzzer contacts. If contacts are clean

and trouble persists, bend the vibrator

closer to the magnet. If this does not

correct the malfunction, replace the

buzzer.

f. Short across the terminals successively at the lightning arrester on the

buzzer or flasher side, then on the anemometer side, and last, create a short

at the anemometer itself by touching

the lead wires together.

g. If buzzer sounds or lamp lights each

time the above shorts are made, the

trouble is in either the anemometer

lead wires or the anemometer itself.

5. If buzzer or flasher operates continuously when the switch is closed, check all circuits for shorts or bare wires.

CROSS REFERENCE: Description 3.1;

Operation 13.1.

WIRING DIAGRAMS

ihgi—# MECHANICAL WIND COUNTER

TWO CONDUCTOR

Figure 20.1.— Wiring diagrams: Upper, Buzzer or

flasher; lower, mechanical wind counter.

599-270 O - 76 - 10 123
Maintenance instructions for the more commonly used mechanical wind counters follow.

20.2 FORESTER 9X156 WIND

COUNTER, MODEL 1

Refer to figure 20.2.

Annual Maintenance

1. Clean the exterior of the counter. Use

nonflammable instrument cleaning solvent to

remove stubborn dirt.

2. Carefully open counter and clean the inside using a soft brush. Use instrument cleaning

solvent to remove stubborn dirt.

3. Check all electrical connections inside

the counter. Tighten loose connections and resolder broken connections. Use rosin-core

solder.

4. Reassemble counter and check the timer

for accuracy. If necessary, adjust timer setting

as follows:

a. Loosen locking lug.

b. Rotate timer stop to correct position.

c. Tighten locking lug.

5. Inspect battery leads and install a fresh

battery. Remove any dirt or corrosion from

battery leads and replace any worn or broken

lead wires.

6. Inspect anemometer leads and clean and

replace as necessary.

7. Test wind counter by attaching a contacting anemometer (fig. 20.1). Spin the cups

by hand and observe if the counter advances

each time the anemometer closes a contact.

The counter can also be tested by touching the

counter leads together at 1- to iy2-second

intervals.

Periodic Maintenance and

Troubleshooting

1. Occasionally check the timer against a

stopwatch. Reset if necessary.

2. In the event of counter failure, proceed

as follows:

a. Replace battery and check battery

lead wires for visible signs of wear or

breaks.

b. Remove one anemometer lead wire

from the counter.

Figure 20.2. —Forester 9X156 Wind Counter,

Model 1.

c. Set timer and while it is running, use a

short piece of wire and short across

from one binding post to the other,

alternately making and breaking the

circuit.

d. If counter advances each time the circuit is closed, the trouble is in the anem ometer or the anemometer lead

wires. Check the lead wires with a continuity tester (see section 19.4) and

replace if necessary. If lead wires are

sound, refer to maintenance instructions for anemometer and check contacts and electrical connections

accordingly.

e. If counter fails to advance when circuit is closed, and all the previous

steps have been followed, test battery

lead wires for continuity (see section

19.4). If trouble is not found here, the

counter should be checked by an electronic technician.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.6; Operation 13.1.

20.3 HAYTRONICS TOTALIZING

WIND COUNTER

Refer to figure 20.3.

This instrument has the same maintenance

requirements as the preceding Forester 9X156.

124
6. Inspect battery lead wires (Fand G) for

wear, breaks, or corrosion. Clean, repair, or replace as necessary. Install a fresh, heavy-duty,

6-volt lantern battery that has screw posts.

7. Inspect anemometer lead wires for wear,

breaks, or corrosion. Clean, repair, or replace

these wires as necessary.

8. Push up on the right-hand switch of the

counter front. This is the "on" position and

should cause the right-hand counter wheel to

advance one count. This is a self test of the

instrument.

If the counter does not advance one count

when the power switch is turned "on," do any

of the following until the trouble is corrected:

a. Check battery polarity.

Figure 20.3. — Haytronicstotalizing wind counter.

The main difference between them is that the

Haytronics has an "off-on" switch rather than a

timer dial. With this in mind, follow the maintenance instructions for the Forester 9X156

wind counter.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8.6; Operation 13.1.

20.4 STEWART ELECTRONIC

ODOMETER

Refer to figure 20.4.

Annual Maintenance

1. Clean exterior of counter. Use instrument cleaning solvent to remove stubborn dirt.

2. Open counter by lightly squeezing on the

sides and slowly pulling the two sections

straight apart. Flexible wires on the two

switches will allow the sections to be separated

sufficiently to reach the interior.

3. Clean interior of counter with instrument cleaning solvent and a soft brush.

4. Check all connections inside the counter.

Tighten loose connections and resolder broken

connections. Use rosin-core solder.

5. Carefully close the counter box, making

sure not to pinch any of the interior wiring

between the two sections or to disturb the transistors in their sockets. Loop the switch wires

into accordion folds and then squeeze the sides

of the box and slide the front cover (A) slowly

and squarely onto the back section.

Figure 20.4. — Stewart electronic odometer: A, Front

cover; B, mechanical counter; C, test lamp; D, rubber grommet; E, fuse; F, negative battery wire; G,

positive battery wire; H, anemometer ground wire

(positive) spring clip; /, anemometer wire negative

spring clip; J, counter "off-on" switch; X, test lamp

"on" switch.

125
b. Test battery for power or install a

fresh one.

c. Check all lead wires with a continuity

tester (see section 19.4).

d. Open counter and replace fuse (E) on

the circuit board. Use 3AG, iy2-amp

Littlefuse #31201.5, or equivalent.

9. Attach anemometer, spin the cups, and

hold the left-hand switch down. This should

cause the test lamp to light each time the anemometer contacts close. This is a test of the

anemometer circuit.

If the lamp does not light, do any of the

following until the trouble is corrected:

a. Check battery polarity.

b. Test battery for power or install a

fresh one.

c. Open counter and replace the lamp

(C). Use a GS48 lamp, or equivalent.

d. Check anemometer lead wires with a

continuity tester.

e. Check anemometer contacts and electrical circuit.

Periodic IVIaintenance and

Troublesliooting

1. Replace battery if required. The decline

in brilliance of test lamp can be used as a guide

for battery replacement.

2. Before each observation, test instrument

by turning power switch "on" and seeing if the

counter advances one count. If there is no advance, see item 8, Annual Maintenance.

3. Before each observation, depress switch

under test lamp and check to see that lamp

lights when anemometer contacts close. If

lamp does not light, see item 9, Annual

Maintenance.

CROSS REFERENCE: Description 3.1; Installation and Exposure 8,6; Operation 13.1.

126
CHAPTER 21

Wind vanes are designed for trouble-free

operation over long periods of time. Annual

maintenance consisting of cleaning, lubrication, and general refurbishing is usually sufficient to keep an instrument in good operating

condition.

Simple, nontransmitting wind vanes require

maintenance that will insure free turning in

light winds. Inspect for friction, binding, and

excessively worn parts.

At least once a year the arrow, or pointer,

should be removed from the spindle and

cleaned with instrument cleaning solvent. The

spindle should be cleaned also and then lubricated with two or three drops of anemometer

oil. Inspect all parts for excessive wear and

damage such as bent spindle or arrow that

could cause binding or irregular turning. If appropriate, repaint worn surfaces (not the spindle) to guard against corrosion and to enhance

general appearance.

21.1 STEWART WIND DIRECTION

SYSTEM

Annual Maintenance

Wind Vane

Refer to figure 21.1.

1. Loosen the setscrew on the body ofthe

arrow (where the shaft and body meet) and

remove the arrow (A) from the spindle (D).

WIND VANES

2. Clean the arrow (A) and the wind vane

spindle (D) with instrument cleaning solvent.

3. Loosen the four corner screws and remove the front housing cover (B).

4. Clean the commutator ring with instrument cleaning solvent. A small, soft brush or

cotton swab will iiid this operation.

5. If it has not already been done, note

what color wire is attached to each binding post

(F).

6. Remove the lead wires one at a time and

clean all dirt and corrosion from the ends ofthe

wires as well as from the binding posts.

Figure 21.1. — Stewart wind direction system —the

electric wind vane component: A, Arrow; B, front

cover; C, orientation scribe mark;D, spindle; £, contact roller; F, terminal block binding post; G, anemometer wire binding post; H, ground connection

screw; /, multiple conductor cable; J, nut and compression sleeve.

127
Figure 21.2. — Stewart wind direction system — the

wind indicator dial: A, Cabinet; B, indicator panel;

C, land socket;!), lamp socket terminal;£, anemometer flasher unit; F, front panel screws; G, multiple

conductor cable; íí, battery cable.

7. Replace wire leads and tighten all

connections.

8. Inspect front housing cover gasket.

If it is worn, torn, or otherwise damaged and

will no longer provide a moistureproof seal,

replace it with a new one cut from similar

material.

9. Replace front housing cover.

10. Put three drops of anemometer oil on

the spindle (D), just above the top bearing.

11. Replace arrow and tighten set screw.

Wind Direction Indicator.

Refer to figure 21.2.

1. If battery is attached, detach and

discard.

2. Loosen comer screws (F) and remove

front panel (B).

3. Clean dust from interior of cabinet (A).

4. Inspect electrical connections (D) and

remove any dirt or corrosion.

5. Repair loose connections by soldering

them in place. Use rosin-core solder.

6. Attach a fresh 6-volt lantern battery;

spin the attached wind vane arrow and check to

see that all indicator lamps light.

7. If a lamp does not light, replace it with

one that is known to be good.

8. To replace a lamp, first remove the protective lens by turning counterclockwise. Grip

lamp with a short piece of rubber tubing and

also turn counterclockwise. Replacement lamp

should be GE #46, or equivalent, and have a

blue bead just below the element. Be sure to

replace this protective lens after installing a

new lamp.

9. After installing each new lamp, spin

wind vane arrow ageiin. If lamp still fails to

light, check for breaks and shorts in wires and

connecting cable (see section 19.4).

10. When all lamps are "on," replace front

cover.

Periodic (Maintenance

1. The passage of current through the contacts retards both the buildup of corrosion and

the accumulation of dust particles and oil film

on the contact surfaces. For this reason, it is

suggested that the indicator lamp be left "on" a

good portion of each day.

128
2. Whenever lamps become dim, replace the

battery.

CROSS REFERENCE: Description 3.2; Installation and Exposure 8.7.

21.2 OTHER WIND DIRECTION

SYSTEMS

Other wind direction systems exist that are

capable of supplying data for fire-weather purposes (fig. 21.3). Some of these systems are

combined with £in anemometer to supply both

speed and direction data. Maintenance ofthese

units is often complicated and many are sealed

units requiring factory service. Follow manufacturer's instructions regarding maintenance

ofsuch instruments.

Figure 21.3. — Wind direction system using generator

type anemometer and contacting wind vane. Wind

direction is indicated by lights; windspeed by arrow

on dial.

129
CHAPTER 22

RAIN GAGES

Maintenance requirements for nonrecording

rain gages are similar; thus, they are treated as a

group in this section. Recording rain gages, on

the other hand, have differing maintenance requirements depending on type, make, and

often even on the model. If at all possible, the

instruction book provided with the instrument

should be referred to before attempting any

major maintenance on recording rain gages.

22.1 NONRECORDING RAIN GAGES

Nonrecording rain gages are perhaps the

easiest of all fire-weather station instruments to

maintain. Nevertheless, the few simple requirementslisted below should be followed for accurate measurement of precipitation.

Annual Maintenance

1. Carefully check both the measuring tube

and the overflow cylinder for leaks and dents.

Repair or replace these components as necessary.

2. Check the rim of the collector, or funnel.

It should be perfectly round (except the small

wedge-shaped gage), knife-edge sharp, and free

of nicks, dents, and other irregularities. Repair

or replace as necessary.

3. Thoroughly clean inside of measuring

tube using hot water and a brush.

4. Check the measuring stick. If markings

are faded or ifstick is dirty, clean or replace.

5. On the plastic models that have graduated cylinders it may be necessary to occasionally renew markings. This can be done by using

the techniques described for thermometers (see

section 16.2).

Periodic i\1aintenance

1. Check firmness level and plumb of rain

gage support. Repair as necessary.

Figure 22.1. — Checking level on standard rain gage.

130
2. Keep top of gage level. Check periodically by laying a carpenter's level across the top of

the collector (fig. 22.1). Adjust as necessary.

3. Keep overflow cylinder and measuring

tube free of dirt and debris. Do not allow debris

to collect in funnel. Empty measuring tube

after each measurement.

4. Do not handle the graduated part of the

measuring stick with hands. Always hold stick

atthe upper end.

5. During freezing weather, remove funnel

and measuring tube to preventice damage.

CROSS REFERENCE: Description 4.1; Installation and Exposure 8.8; Operation

14.1-14.3.

22.2 TIPPING BUCKET RAIN GAGE

Refer to figure 22.2.

Specific maintenance requirements will vary

depending on model and manufacturer. The instrument manual provided by the manufacturer should be consulted for detailed information on maintenance and calibration.

Annual Maintenance

1. Discontinue use of tipping bucket rain

gage in freezing weather unless the instrument

contains a heating unit.

2. Check rim of collector (A). It should be

perfectly round and free of nicks, dents, and

other irregularities. Repair as necessary.

3. Remove storage container (E) and then

clean and check for leaks.

4. Remove collector (B) and clean all moving parts with a soft brush and instrument

cleaning solvent. Be sure to use a cleaner that

does not attack painted surfaces.

5. Check all parts for wear. Replace worn

parts.

6. Check tipping bucket (C) action. Eliminate any binding.

7. Lubricate sparingly the pivots of the

bucket and the V bearing in the support

bracket. Use a light, nongumming instrument

oil.

8. Do not attempt to adjust position ofthe

calibration stop screws (D) located in the supporting bracket below the cups unless complete

calibration instructions are available. CalibraFigure 22.2. — Tipping bucket rain gage: A, Collector

rim or knife edge;ß, collector; C, tipping bucket; 0,

calibration stop screw; E, water storage container;

F, cable to recorder.

tion is set at the factory and usually does not

require modification unless the instrument has

been subjected to very rough handling.

Periodic Maintenance

1. Keep collector free of debris.

2. Wipe out tipping bucket with a clean

cloth weekly.

3. Wipe bucket pivots and support bracket

V bearing with oily cloth weekly.

4. Periodically check recorded precipitation with measured amount of water in storage

container.

Recorder Maintenance

A variety of recorders can be used with tipping bucket rain gages. Refer to the appropriate

instruction manual for maintenance requirements. If a drum type reader is used, maintenance instructions given in sections 18.3 and

18.4 may apply.

CROSS REFERENCE: Description 4.1; Installation and Exposure 8.9.

131
22.3 WEIGHING RAIN GAGE

Refer to figure 22.3.

Maintenance requirements of the weighing

rain-gage pen, pen arm assembly, chart drive

assembly, and clock are identical to the requirements prescribed for similar components ofthe

hygrothermograph. For this reason they are

not repeated here (see chapter 18).

General Maintenance

The following general maintenance items

should be performed atthe end of each season's

use or every 6 months if the gage is operated

year-round. Refer to manufacturer's instrument manual for detailed instructions.

1. Remove collector and outer case. Clean

all moving parts thoroughly using instrument

cleaning solvent applied with a soft brush. Do

not use solvents that attack painted surfaces.

2. Check linkage system, spring, and other

moving parts for wear and other evidence of

binding or excessive friction.

3. Sparingly lubricate bearings of all moving parts (except chart drive assembly) with a

light, nongumming instrument oil.

4. Scrub bucket inside and out to remove

accumulated dirt, grime, and corrosion.

5. Check level of fluid in dash pot (I). Add

necessary dash pot fluid to bring level to within

one-fourth inch of the top of the dash pot.

Dash pot fluid is available from most instrument supply houses or directly from the rain

gage manufacturer.

6. Check weighing mechanism for accuracy

by placing 29.0 ounces in the bucket for each

inch of rain. (Bendix-Friez Model 775CS requires 72.5 ounces for each inch of rain.) Make

necessary thumbscrew (D) adjustments to

bring pen to 1-inch level on chart. Rain gage

calibration weights are available from weather

instrument supply houses or from rain gage

manufacturers (fig. 22.4).

7. Refer to sections 18.1 to 18.4 for general

maintenance requirements for pen, pen arm

assembly, chart drive assembly (B), and clock.

Calibration

If the accuracy of a weighing rain gage is

questioned, do the following before trying

recalibration:

Figure 22.3. — Weighing rain gage — weighing and recording assembly: A, Weighing platform; B, chart

drive assembly; C, stop screw; D, spring adjusting

screw; E, thumb nut (red); F, linkage assembly; G,

magnification bar (first traverse);//, magnification

bar (second traverse);/, dash pot;J, pen lifter.

Figure 22.4. — Calibration weights for recording rain

gages.

132
1. Check the chart installation. The chart

must be firmly seated against the flange along

the lower end of the chart drum (B).

2. Check chart drum (B). It must be properly seated on the spindle or arbor. The external

gears must be meshed.

3. Check to see that there are two spacing

washers between the base of the gage and the

large stationary gear at the base of the spindle

or arbor.

4. Check mechanical condition of the gage.

Look especially for points of undue friction in

the linkage.

After having checked the above items,

proceed to check present calibration as follows:

5. Place bucket on weighing platform (A).

6. Zero the pen arm using the red knurled

thumb nut (D). The pen should be on the zero

line of the chart.

7. Add to the bucket weights (fig. 22.4) the

equivalent of 1 inch of rainfall (29.0 ounces).

Add 12 weights, one at a time, and note the

chart value indicated as each weight is added. If

the chart values observed are incorrect for the

weight added, the instrument is in need of

calibration.

If there is insufficient or nonuniform motion of the pen over the first and/or second inch

of chart when the bucket and weights are

added, but correct or uniform motion of the

pen is obtained thereafter, then the spring

probably needs replacement.

This malfunction of the spring can be

checked by observing the action of the spring

when the empty bucket and the weights are

added to the platform. After the bucket and a

weight are added, the spring should have started to open. If no space can be observed between each effective coil, the spring is defective

and should be replaced.

Further calibration should not be attempted

without the detailed instructions and schematic diagrams provided by the manufacturer.

These are either contained in the instrument

manual (Bendix-Friez) or are available by request from the manufacturer (Belfort).

CROSS REFERENCE: Description 4.1; Installation and Exposure 8.9; Operation 14.4.

133
CHAPTER 23

FUEL MOISTURE

STICKS

A fuel moisture stick should be discarded

after one season's use (more often in areas of

rapid weathering); hence, there is no annual

maintenance requirement. While in use, a few

simple maintenance items require the observer's attention.

Dirt, oil, and dust add to the weight of the

stick and can interfere with normal moisture

changes of the stick. The stick, therefore,

should be kept clean. Prior to each weighing,

dust the stick with a soft, clean paint brush. Do

not brush the stick if it is wet. Wait until it is

dry.

Cover hands with clean gloves or use a clean

cloth or a clean piece of hard-finish paper to

pick up stick for weighing. Handling stick with

bare hands might contaminate it with oil and

dirt.

A properly installed duff bed will prevent

mud from' splashing up on the stick during

heavy rains. In the event that the stick does

become mud splattered, allow mud to dry and

then brush off (do not rub in) the dirt.

Do not remove the metal hook at the end of

the stick as its weight is included in the 100-

gram dry weight of the stick. Similarly, guard

against scratches, chips, breaks, etc. If they

occur, replace with a new stick.

CROSS REFERENCE: Description 5.1; Installation and Exposure 8.10.

134
CHAPTER 24

FUEL MOISTURE

SCALES

When properly installed in a weatherproof

shelter, the fuel moisture scale requires minimum maintenance. Annual cleaning and periodic calibration checks are the major items of

concern.

Specific maintenance instructions for the

scales most often used to weigh fuel moisture

analogs are presented in the following sections.

24.1 THE APPALACHIAN SCALE

(Forester Model 9X100, BendixFriez)

Refer to figure 24.1.

Annual Maintenance

1. Disassemble scale and clean all parts

using an instrument cleaning solvent that is

nonflammable.

2. Check the beam (E) for straightness. If

bent, repair or replace.

3. Check wire hook (J) at rear of beam. It

should be well-formed, straight, and should

swing free.

4. Clean and check the bearing hole on

front (C) and rear (D) pivot plates. If excessively worn, replace.

5. Check the beam pivot shaft. It must be

straight. If bent or excessively worn, repair or

replace.

Figure 24.1. — The Appalachian scale; A, Backplate

with calibrated scale; B, beam stop plug; C, front

pivot plate; D, rear pivot plate; E, beam; F, beam

pivot shaft; G, beam pivot shaft spacer; H, sliding

weight setscrew; /, sliding weight; J, beam link or

hook; K, 100-gram test weight; L, mounting bracket

wing nut.

6. Reassemble, mountin shelter; check first

the shelter and then the scale for level. Both

must be square and plumb.

7. Check adjustment. The sliding weight (I)

must be movable by moderate hand pressure.

Adjust by using the set screw (H) on top of

sliding weight. Set sliding weight at 100 and

135
hang 100-gram test weight on hook at end of

pointer. Pointer should indicate zero on the

graduated arc scale. If the pointer does not indicate zero, loosen wing nuts (L) and adjust entire backplate (A) up or down. Do not adjust

zero with sliding weight on beam as this, in

effect, changes ovendry weight of the fuel stick.

Periodic IVIaintenance

1. Dust with soft brush whenever a buildup

of dirt is visible.

2. Occasionally check both shelter and

scale for level and plumb.

3. Prior to each use of scale, check calibration with test weight (K). Make only very fine

adjustments with sliding weight (see item 7,

above).

CROSS REFERENCE: Description 5.3; Installation and Exposure 8.11; Operation 15.1.

24.2 REGION 6 SCALE

This scale is almost identical to the Appalachian scale except that it has no sliding weight

on the beam. Maintenance instructions, except

for calibration, are as given above for the

Appalachian scale. To calibrate, hang 100-gram

weight on hook at end of beam. If the beam

does not read zero, loosen the wing nuts that

hold the backplate to the mounting plate and

turn the scale on the upper right-hand bolt until

the pointer reads zero. Tighten wing nuts and

check pointer. Repeat until zero is obtained.

CROSS REFERENCE: Description 5.3; Installation and Exposure 8.11; Operation 15.1.

24.3 WILLIAI\/IS POCKET

FIRESTICK IVIOISTURE SCALE

Refer to figure 24.2.

The primary maintenance requirement of

this sturdy little instrument is periodic cleaning. Apply instrument cleaning solvent and use

a toothbrush to scrub away accumulated dirt,

especially from the threads on the balance

beam (D) and the handle (A).

The central knife edge (E) of the scale is

spring-loaded to protect it from injury, and is

adjusted to move freely under the screw

Figure 24.2.— Williams Pocket Firestick Moisture

Scale: A, Handle and locking screw; B, cover and

lOO-gram test weight; C, balance weight;D, balance

beam;£, knife edge;^, hook.

Figure 24.3. — Forester 9X120 portable fuel moisture

scale, Chisholmmodel: A, Scale;B, scale beam support bracket; C, fuel stick suspension loop;I>, pointer; E, scale beam shaft; F, scale beam weight; G,

100-gram test weight: H, scale beam weight adjustment nut.

heads. This adjustment never needs to be

changed and is correct when it leaves the factory.

The cover (B) of the scale also serves as a

100-gram test weight. For this reason do not

engrave on it, stick plastic marking tape on it,

or otherwise add to or subtract from its original weight.

CROSS REFERENCE: Description 5.3;

Operation 15.3.

24.4 PORTABLE FUEL IVIOiSTURE

SCALE-CHISHOLM IVIODEL

Refer to figure 24.3.

To check calibration, hang the 100-gram

test weight on the loop (C) provided, hold the

136
scale level, and check to see that pointer (D)

indicates zero on the scale (A). If pointer does

not indicate zero, loosen nut (H) at weight

end of the scale beam and adjust weight until

zero is obtained. Tighten nut and recheck. Always be sure to hold the scale level.

CROSS REFERENCE: Description 5.3;

Operation 15.2.

24.5 TRIPLE BEAM BALANCE

Refer to figure 24.4.

Annual Maintenance

1. Dust thoroughly with a soft, clean

brush. Wash top of platform (A) if necessary.

2. Remove the bearing cover plates (E and

F). Blowing the bearings out with a dry air

blast is the recommended method of cleaning.

On older models it may be necessary to use a

toothbrush to remove stubborn dirt.

3. Clean any accumulated debris from the

magnet faces located under the platform (A)

in the balance cup (B). Press a piece of Scotch

tape against the magnet face to pick up attracted material which might interfere with

the damping vane.

4. Replace the bearing plates. Take care

not to damage the bearings or dull the knife

edges.

5. Check knife edges, especially on older

models. If dull, the scale will react sluggishly.

Sharpen or replace dull knife edges.

Periodic Maintenance

1. Remove dust from top of platform before each use.

2. Periodically check the scale's balance

since foreign material may accumulate on the

platform beams and cause a slight change in

the balance position. Do this on a fairly flat

and level surface.

With an empty pan and all the weights at

zero, the pointer should oscillate the same

number of divisions above and below the center line, or zero, and eventually come to rest

at zero. Very lightly tap a bearing cover so the

pointer will not stop prematurely.

If the scale does not balance, adjust the

knurled adjusting knobs (two knobs act toFigure 24.4. — Triple beam balance: A, Platform; B,

balance cup; C, knurled adjustment knob; D, friction plate; E, bearing cover; F, bearing cover; G,

base;ii, poise (sliding weights);/, beam.

Figure 24.5. — Harvard balance: A, One-half-inch fuel

sticks; B, 100-gram weight; C, pan; D, knurled adjusting knob; E, main bearing; F, main bearing cover

plate; G, lock.

gether as lock nuts on older models.) Screw

the knobs out if the pointer is low, screw in if

the pointer is high. When proper adjustment is

obtained, lock the nuts tightly together, then

recheck the pointer.

3. Check the zero balance whenever the

balance is moved since it will be affected by a

change in the inclination of the working surface.

CROSS REFERENCE: Description 5.3;

Operation 15.4.

24.6 HARVARD BALANCE

Refer to figure 24.5.

Maintenance instructions for the Harvard

balance are similar to those for the triple

beam scale.

CROSS REFERENCE: Description 5.3;

Operation 15.5.

137
LITERATURE CITED

Barney, Richard J.

1962. Appalachian scale shelter. U.S. Forest Serv. Res. Note 88, 7 p., illus.

In termountain Forest and Range

Exp. Sta., Ogden, Utah 84401.

Breuer, Erwin H.

1968. Remote measurement of wet and

dry bulb temperatures. USDA Forest Serv. Fire Contr. Notes 29(4):

14-15, illus.

Byram, George M.

1940. The Appalachian fuel moisture

scale. J. Forest. 38: 493-495, illus.

Corbett, Edward S.

1967. Measurement of precipitation on

experimental watersheds. Nat. Sei.

Found. Advance. Sei. Seminar Proc.

1965: 107-129, illus.

Countryman, Clive M.

1971. This HUMIDITY business: what it

is all about and its use in fire control. 15 p., illus. USDA Forest

Serv., Pacific Southwest Forest and

Range Exp. Sta., Berkeley, Calif.

94701.

Cramer, Owen P., and Ralph H. Moltzau

1968. Wind instrument mountings for

above-the-cab lookout exposure.

USDA Forest Serv. Res. Note

PSW-175, 9 p., illus. Pacific Southwest Forest and Range Exp. Sta.,

Berkeley, Calif. 94701.

Davis, Kenneth P.

1959. Forest fire: control and use. 584 p.,

illus. New York: McGraw Hill Book

Co.

Deeming, John E., and James W. Lancaster

1971. Background, philosophy, implementation — National fire Danger Rating

System. USDA Forest Serv. Fire

Contr. Notes 32(2): 4-8, illus.

Deeming, John E., James W. Lancaster,

Michael A. Fosberg, R. William Furman,

and Mark J. Schroeder

1972. The National Fire-Danger Rating System. USDA Forest Serv. Res. Pap.

RM-84, 165 p. Rocky Mt. Forest

and Range Exp. Sta., Fort Collins,

Colo. 80521.

Fischer, William C, William R. Beaufait, and

Rodney A. Norum

1969. The hygrothermoaerograph —

construction and fire management

applications. USDA Forest Serv.

Res. Note INT-87, 8 p., illus. Intermountain Forest and Range Exp.

Sta., Ogden, Utah 84401.

Gisborne, H. T.

1933. The wood cylinder method of measuring forest inflammability. J. Forest. 31: 673-679.

Hardy, C. E.

1953. Half-inch fuel-moisture stickshow they are made. U.S. Forest

Serv. Fire Contr. Notes 14(4): 1-8,

illus.

Hauck, Charles A., and Dee F. Taylor

1968. Project Theo surface networks. Paper presented at Amer. Meteorol.

Soc.-Soc. Amer. Forest. Conf. on

Fire and Forest Meteorol., Salt

Lake City, Utah, March 12-14. 9 p.,

illus.

Hayes, G. L.

1942. A discussion of hygrographs. U.S.

Forest Serv. Res. Note 25, 6 p.

Northern Rocky Mountain Forest

and Range Exp. Sta., Missoula,

Mont. 59801.

Jones, Douglas M. A.

1969. Effect of housing shape on the catch

of recording gages. Mon. Weather

Rev. 97(8): 604-606, illus.

Keetch, John J.

1966. Quality control in fire danger rating. USDA Forest Serv. Fire Contr.

Notes 27(4): 11,16.

138
Kidd, W. J., Jr.

1960. The advantages of using ethylene

glycol in seasonal storage precipitation gages and a method for computing the initial charge. J. Forest.

58: 882-884, illus.

Lewis, Frank E.

1966. Fire weather telemetry. USDA Forest Serv. Fire Contr. Notes 28(1):

14, 16, illus.

Meeks, Charles H.

1968. Report on the results of tests conducted with the humidity element

of the Friez hygrothermograph model 594. U.S. Dep. Comm., ESSA,

Nat. Severe Storms Lab. Tech. Circ.

5, 8 p., illus.

Middleton, W. E. K., and A. F. Spilhaus

1953. Meteorological instruments. Ed. 3,

286 p., illus. Canada: University of

Toronto Press.

Murray, John R., and Clive M. Countryman

1968. A portable station for recording fire

weather data. USDA Forest Serv.

Res. Note PSW-182, 7 p., illus.

Pacific Southwest Forest and Range

Exp. Sta., Berkeley, CaUf. 94701.

Pirsko, Arthur R., and Paul G. Scoweraft

1969. Adequate presuppression manning

depends on accurate fire weather

observations. USDA Forest Serv.

Fire Contr. Notes 30(1): 7-8.

Ryan, Paul W.

1970. Portable calibrator developed for

anemometers. USDA Forest Serv.

Fire Contr. Notes 31(3): 14-15,

illus.

Schroeder, Mark J., and Charles C. Buck

1970. Fire weather. USDA Handbook

360, 229 p., illus. Wash., D. C.

Smith, L. P.

1970. The difficult art of measurement.

Agr. Meteorol. 7(4): 281-283.

Society of American Foresters

1958. Forest terminology. Ed. 3, 97 p.

Washington, D. C: Society of

American Foresters.

Taylor, Dee F.

1963. Mortarboard psychrometer. U.S.

Forest Serv. Res. Pap. SE-5, 12 p.,

illus. Southeastern Forest Exp. Sta.,

Asheville, N.C. 28802.

Thornthwaite, C. W.

1939. Handbook for climatologists. Part

V. Instructions for the measurement of evaporation from natural

surfaces. 22 p., illus. Washington,

D.C.

USDA Forest Service

1959. Belt weather kit. U.S. Forest Serv.

Fire Contr. Notes 29(4): 122-123,

illus.

1962. Wildland fire danger rating. Pacific

Southwest Forest and Range Exp.

Sta., Berkeley, Calif. 94701.

1964a. Aluminum weather instrument

shelter. ED&TC Rep. 5100-13, 10

p., illus. Washington, D.C.

1964b. National fire-danger rating system

handbook. FSH 5109.11. Washington, D.C: USDA.

1964c. Portable fire-weather station.

Equip Tips 5100, 5 p., illus. Missoula, Mont.

1969. Remote wind measurements. USDA

Forest Serv. Fire Contr. Notes

30(1): 16, illus.

U.S. Department of Commerce, ESSA

1970. Weather Bureau observing handbook

No. 2. 77 p., illus. Substation Observations, Superintendent of Documents, Washington, D.C.

Williams, D.C.

1964. Forest fire danger manual. Can.

Dep. Forest Res. Br. Pub. 1027,

28 p., illus.

World Meteorological Organization

1956. International cloud atlas. Vol. 1,

155 p., illus. Geneva, Switzerland.

1969. Guide to meteorological instrument

and observing practices. Ed. 3,

WMO-No. 8, TP. 3. Geneva,

Switzerland.

139

599-270 O - 76 - 11
APPENDIX

FIRE-WEATHER STATION CONDITION REPORT

INSTRUCTIONS: This form may be used for several purposes--(1) as a station location record--Secti on 1-

(2) as an equipment inventory record--Sect i on 2; (3) as an inspection report--Sect i on 3;'

and [k) as an observer se 1f-training guide--Secti on 3.

SECTION 1 - STATION LOCATION RECORD

Enter information or check {y) appropriate items.

Station name

Operating agency_

State

Station number_

Local unit

County

Year established

Operating season

T R Section

Topography: Flat or gently rolling , hilly or broken

mountain top , mountain slope .

Aspect: N^ , S

mounta in va 1 ley

, E _, W

SECTION 2 - STATION EQUIPMENT RECORD

Enter information or check ( v/ ) appropriate items.

Instrument shelter: Cotton region

Maximum-minimum thermometer: Standard

Psychrometer: Electric fan ~

Hygrothermograph: Make_

Anemometer: Make

Wind counter: Type

Wind vane: Type ~"

Wind direction indicator : Type

Rain gage (nonrecording): Forest Service type

Recording rain gage: Type ~

other

othe r

other

chart period_

mode 1

make

make

make

Fuel moisture analog: 1/2-inch sticks_

Fuel moisture scale: Type

Weather Service type

make ~

other

make

Enter an X in either Yes or No col

REMARKS.

SECTION 3 - INSPECTION REPORT AND SELF-TRAINING GUIDE

umn according to condition. Explain all No entri.es, by number, in

Station Location

1. Adequately represents area of concern.

2. Allows for long term operation.

3- Accommodates instrument exposure

requi rements.

a. Dust sources at least 100 ft. on

wi ndward.

b. Moisture sources at least 100 ft.

on windward.

c. Large reflective surfaces a

distance equal to their height

away.

d. Paved or black topped areas at

least 50 ft. away.

e. Large obstructions at least a

distance equal to their height away.

f. Distinct changes in topography

lacking.

Station Layout

h. Allows free flow of air.

5. Allows full sun exposure.

6. Tall vegetation cleared for 20 ft.

around station.

All vegetation on station grounds

less than k in. high.

Station grounds not irrigated. '

9. Fence of open type construction. I

10. Fence less than k ft. high. !

Yes No

i

19

20.

21.

22.

23.

25.

26.

27.

28.

29.

30.

31.

Instrument Shelter

Cotton region or other approved

des ign.

Shelter floor h ft. above ground.

Shelter firmly secured to stand.

Stand firmly secured to ground.

Installation level and plumb.

Door faces away from sun.

Painted glossy white, inside and

out.

Inside clean of dirt and dust.

Only temperature sensitive instruments in shelter.

Standard Maximum-Minimum Thermometers

Yes No

Exposed in instrument shelter.

Townsend Support securely mounted

on crossboard.

Townsend Support spinning clamp

on bottom.

Minimum bulb on left, in top clamp.

Minimum bulb 5° below horizontal.

Maximum bulb on left, in lower

clamp.

Maximum bulb 5° above horizontal.

Thermometers clean and legible.

Thermometer columns intact, not

separated.

Maximum column does not "retreat."

Minimum index floats freely.

Maximum spins freely in its clamp.

140
32.

33.

3^.

35.

36.

37.

38.

39.

^0.

Al.

hl,

A3.

A5.

A6.

kl.

A8.

49.

50.

51.

52.

53.

Fan Psychrometer

Exposed in instrument shelter.

Firmly mounted, clear of maximum

thermometer.

Wet bulb wick clean.

Wet bulb wick extends 1 in. above and

below bulb.

Thermometers clean and legible.

Thermometers agree within 1/2° when

both bulbs dry.

Water and container present and clean.

Polarity of battery wires correct.

Fan operates at top speed, batteries

fresh.

Hygrothermograph

Exposed in instrument shelter.

Clear of maximum thermometer.

Hair element intact and clean.

Temperature element dust free.

Pens inking properly.

Both pens indicate the same chart time

Chart time correct.

Range and spread of pen arms appear

correct.

Current chart values agree with

psychrometer values.

Anemometer

5A.

55.

56.

57.

58.

59.

60.

61.

62.

63.

Yes No

d.

f.

Located for representative readings.

Pole adequately supported, windfirm.

Lightning protection adequate.

Cups exposed at 20-ft. standard height.

a. Level ground, low covei 20 ft.

b. High ground in rolling topography20 ft.

c. Low ground in rolling topography--

20 ft. plus average depth of low

spot.

Dense ground cover--20 ft. plus

average height of cover.

Scattered ground cover--20 ft. plus

one-half average height of cover.

Sparse ground cover--20 ft. plus

one-third average height of cover.

Periodic height adjustment possible.

Easy access to anemometer provided.

Cups turn freely in light winds.

Mechanical Wind Counter

Lightning protection adequate.

Weatherproof wire used.

Polarity of battery wires correct.

Voltage and line length in proper

bal anee.

Counter advances one digit at a time.

Timer runs for exactly 10 minutes.

Counter not installed in temperature

shelter.

6A.

65.

66.

67.

68.

69.

70.

71.

72.

73.

Ik.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

93.

3k.

95.

96.

97.

98.

99.

100.

Wind Vane and Indicator

Lightning protection adequate.

Vane oriented with true north.

Vane turns freely in light wind.

Weatherproof wire used.

Indicator readout agrees with vane

di rection.

Polarity of battery wires correct.

Indicator not installed in

temperature shelter.

Standard Rain Gage

Level and plumb.

Gage free of dents, leaks, debris.

Stand firmly attached to ground.

Top of gage 36 in. above ground.

45° angle from top of gage clears

obstacles.

Measuring stick clean and legible.

Recording Rain Gage

Firmly mounted to ground.

Level and plumb.

Pen inking properly.

Chart time correct.

Pen properly zeroed.

Calibration appears correct.

Collector free of dents and debris.

Pail clean, free of leaks.

Fuel Moisture Sticks

Duff bed 36 in. square, 2 in. deep.

Duff bed over mineral soil, no humus

Duff bed free of living vegetation

Duff bed at ground level, not in

pit.

Stick hook end north, nails down.

Stick clean and undamaged.

Wire racks 10 in. above duff bed.

Wire rods of galvanized wire.

Fuel Moisture Scale

Yes No

Shelter firmly mounted to ground.

Shelter level and plumb.

Shelter weatherproof, in good repair

Scale installed properly, level and

plumb.

Scale clean, dust free.

Scale balances at zero.

Scale balances at 100 grams with

test wei ght.

Balance action free, doesn't bind.

REMARKS:

141
INSTRUMENT SHELTER ANCHOR PIN

Vs" X 3" BOLTS w/WASHERS ^ WIN6 NUTS

smm

&

SMB ----

o;

<—z"—».

^

^ '^ t

^

TOP VIEW

W'x Z"x ^" COLD-ROLL

STEEL PLATE

-WELD

SECTION

VV'DIA.ROD COLD-ROLL

STEEL

-TURNED ON LATHE

NJOT TO SCALE

142
-i-8-

o>

-2'-0'

^—

^U^-íp

^ ' ^

-I I'/»"

3^

BUTT

l'-6"-

METAL DOOR CATCHESHINGED STEEL HASP

3/4'pLrWOOO

SEE DETAIL"A'l

>

r

FRONT VIEW SECTION

WALL MOUNT ATTACHMENT

¡NUT5 ~ljfc~

'WASHER 3/4 PLYWOOD

l^"x I !^" STOVEBOLT

WASHER

'ANEMOMETER MAST

DETAIL "A"

WOT TO SCALE

4" WALL MOUNT

3-D DRAWING

WEATHER STATION ACCESSORY SHELTER

143
2 0"

r

2 día. door

knob (wood}"F^-^

:5i

—^;^

Buff

hinge

3^4

&uff hinge>

^

-Riv

See DefaiTH

%* plywood -*

FRONT ELEVATION

,%V 4"x^"T

SECTION A-A

Washer

A X 3"s+ovebolf

/H" pit/wood

nge

%' plywood door

DETAIL H SECTION B-B

APPALACHIAN SCALE SHELTER

144
Corpcnters level shown

Scale mounting strip-. ^:„ oniition A

Adjus^^^

V^^'^

boi,\<

PERSPECTIVE VIEW

SCALE LEVELING DETAIL

a

/

Nom. 4'x4'-

3?tf^

S!!!SWA*«i¡í!

Pfr

ipumÊ^

LJ _

1^35^

Scale mounting strip

Place one

p\ece of ^ X %*

window trim as

shown for locating

A" 4) hole for Adj. No. 2

SHELTER MOUNTING DETAIL MOUNTING BOARD DETAIL

145
HYGROTHERMOAEROGRAPH

05

(E) Solenoid

(G)Connecting wire

link

(c)windspeed

pen arm

(iï)Pen arm

tongue

HYGROTHERMOGRAPH MODIFICATION

i '( III

(a)Solenoid

mounting

bracket

(R) Solenoid

connecting

loop

BJPen arm mounting

bracket Ô shaft

(A)Bulkhead
HYGROTHERMOAEROGRAPH "»'-»-»^^p^ Pen arm ,

4^

to

Anemometer

Contacts

68 K > R

1 ^

+ 6 V

Rp > 68K

47/jf

)

I >«4

X*

Solenoid

/

^

1

ELECTRICAL CIRCUIT

Parts List

1 - Solenoid

2 — Resistors

I - Capacitor

I - Battery

4 — Transistors

- D.C. Relay; 200 ohm w/silver contacts.(SIGMA-200 or equivalent.)

- R,and R2=68k,i lOVo; 1/2 watt.

- C| = 47juf, 10 volt D.C. ; t 10%.

- 6 volt, lantern type.

- Q, ,and Q3; NPN FAIRCHILD S 7581 or equivalent.

Q2,and Q^; PNP G.E. 2NI303 or equivalent.
INDEX

Accessory shelter, 50

construction detail, 143

Alcohol thermometers, 4-5, 89-90

Alter rain gage shield, 26, 28, 53

Aluminum shelter, 7-8

Analog, fuel moisture, 30-31, 41, 135

Anchor pin, 42-43

construction detail, 142

Anemometers, 16-20, 45-50, 73-76, 108-122

Belfort totalizing, 18, 48, 117-118

buzzers, 17, 74, 123-124

calibration, 109-110

Chisholm Model 2B3C, 114-115

contacting, 16-19, 40, 73-74

counters, 17, 41, 73-74, 123-129

cup, 16-19

dial, 18-19, 45, 74-75, 119-120

flashers, 17, 74, 123-124

Forester Model 9X140, 112-113

Forester Model 9X150, 113-114

Friez dial, 18-19, 45, 119-120

generator, 16, 19-20, 129

height adjustment, 16, 45-48, 75

installation, 46-50

lightning protection, 46-50

maintenance, 108-122

operation, 73-76

pole, 41, 45-46

small Airways, 17, 111-112

Stewart aluminum cup, 115-116

Stewart 4-cup, 116-117

Weather Measure W164 and 164B, 18,

120-121

Appalachian scale, 31, 55, 83, 135-136

Appalachian scale shelter, 31, 45, 55, 135

construction detail, 144-145

Automatic weather station, 56-57

Average humidity, 9

Average temperature, 4

Average windspeed, 18, 73-76

B

Balance, Harvard, 31-33, 86, 137

Balance, Ohaus, 33, 137

Balance, triple beam, 31, 33, 85-86, 137

Belfort hygrothermograph, 101-107

Belfort totalizing anemometer, 18, 48, 117-118

Belt weather kit, 12, 20, 56-57

Bendix-Friez Small Airways anemometer, 17,

111-112

Bendix hygrothermograph, 13, 101-107

Bendix Psychron Model 566, 11, 97-99

Bimetal strip, 4, 13-14

Bourdon tube, 4, 13-14

Buzzer, 17, 74, 123-124

Calibration chamber, 107

Calibration weights, 132-133

Chamber, humidity, 107

Charts, 14-15, 26

Chisholm Model 2B3C anemometer, 114-115

Chisholm scale, 31-32, 84, 136-137

Circuit check, anemometer, 110-111

Clouds, 34-37

classification, 34-35

cover, 34

form, 34, 36

vertical, 34-36

Column, fractured, 89-90

Column, separated, 89-91

Combined maximum-minimum thermometer,

6, 91-92

Condition report, 39, 140-141

148
Contacting anemometer, 16-19, 40, 73-74

Continuity tester, 110-111

Cotton region shelter, 6-7, 40, 42-45

Counter, wind, 16-19, 41, 50-51, 73-75,

123-126

nonreset, 17, 74, 123-126

reset, 17, 73-74, 124

totalizing, 18, 124-126

with 10-minute timer, 17-18, 51, 73, 124

Cup anemometer, 16-19

Current temperature, 4-6

D

Deformation thermometers, 4, 13

Depression, wet bulb, 9

Dewpoint, 4, 9-15

instruments, 9-13

tables, 9

Dial anemometer, 16, 18-19, 45, 74-75,

119-120

Dial thermometers, 4

Digital recording rain gage, 26

Direction, wind, 16, 21, 127-129

Dry bulb,

temperature, 4, 9-10

thermometers, 10-13, 94

Duff bed, 41,53, 134

Dumbbell, 5-6

Duration, precipitation, 25, 28-29

Dwyer wind meter, 20, 75-76, 121-122

E

Electro V psychrometer, 97-99

Electric fan psychrometer, 10, 40, 44, 65,

94-96

Electric odometer, 125-126

Equipment, weather station, 40-41

Exposure, instrument, 44-55

Farmer's rain gage, 25, 80, 130-131

Fencepost rain gage, 25, 80, 130-131

Fence, weather station, 41, 54

Fergusson rain gage, 25-26, 52-53, 80-82,

132-133

Fire-weather station,

condition report, 39, 140-141

equipment, 40

fence, 41, 54

grounds, 41

layout, 41

location, 40

Flasher, anemometer, 17, 74, 123-124

Forester 9X140 anemometer, 112-113

Forester 9X150 anemometer, 113-114

Forester 9X100 Appalachian scale, 31, 83,

135-136

Forester 9X120 Chisholm scale, 32, 84, 136-137

Forester 9X060 electric fan psychrometer, 44,

94-96

Forester 9X050 hand fan psychrometer, 96-97

Forester 9X156 wind counter, 124

Forest Service electric fan psychrometer, 10,

94-96

Forest Service hand fan psychrometer, 11, 96-97

Forest Service rain gage, 22-24, 45, 52, 130-131

Four-inch clear plastic rain gage, 24, 79, 130-131

Fractured thermometer column, 89-90

Friez dial anemometer, 18-19, 45, 74, 119-120

Friez small Airways anemometer, 17, 111-112

Fuel moisture, 30-33

analog, 30-31, 41

duff bed, 53, 134

indicator sticks, 30-31, 83-86, 134

scales, 31-33, 55, 83-86,135-137

screens, 53-54

G

Generator anemometers, 16, 19-20, 129

Gemware Model Electro V psychrometer, 97-99

Grounds, weather station, 41

H

Hair hygrometer, 9-10

Hand fan psychrometer, 10-11, 66, 96-97

Hand-held wind meter, 20, 75-76, 121-122

Harvard balance, 33, 86, 137

Haytronics wind counter, 124-125

Height adjustment, anemometer, 16, 45-47, 75

Human hair element, 10, 14

Humidity, average, 9

Humidity chamber, 107

Humidity, relative, 9-15

Hygrometer, wet- and dry-bulb, 9, 12, 68

Hygrothermoaerograph, 18-19, 44

construction detail, 146

electrical circuit, 147

Hygrothermograph, 4, 10, 13-15,18, 41, 70-72,

101-107

calibration, 15, 71-72, 104-107

149
Chart drive, 13, 103

chart record, 14-15

charts, 14-15

clock, 103-104

exposure, 44

maintenance, 15, 101-107

modification, 18

operation, 70-72

pen arms, 13, 101-103

relative humidity element, 10, 13-15

reliability, 15

temperature element, 13-14

Weather Measure, 44, 101-107

I

Index rod, 5-6

Indicator, wind direction, 21, 50-52, 127-129

Inorganic fuel moisture analog, 30

Installation, fire-weather instruments, 42-55

Instrument Corporation anemometer,

111-112

Instruments,

exposure, 42-55

installation, 42-55

maintenance, 87-137

operation, 59-86

Instrument shelters, 6-8, 42-45

anchor pin, 42-43, 142

cotton region, 6-8, 42-45

portable, 7-8

K

Kind of precipitation, 28-29

Layout, fire-weather station, 41

Lightning protection, 46-50

Liquid-in-glass thermometers, 4-5

Location, fire-weather station, 40

M

Maintenance, 87-137

Markings, thermometers, restoring, 89

Maximum temperature, 4-6, 60-62

Maximum-minimum thermometers, 5-6, 44,

60-62, 91-92

combined, 6, 62, 91-92

Six's, 6, 62, 91-92

standard, 5, 40, 44, 61-62, 91

Maximum thermometer, 5-6, 44, 60-62, 89-90

constriction, 5

operation, 60-62

retreater, 90

Measuring stick, rain gage, 22-23, 130

Mechanical wind counter, 17-18, 41, 50-51,

73-76, 124-126

Mercury thermometers, 4-6, 89-92

Metal tower, 46

Minimum temperature, 4-6, 60-62

Minimum thermometer, 5-6, 44, 60-62, 89-92

Mortarboard psychrometer, 9, 13, 69, 99

Mounts, instrument shelter, 42-43

Mounts, rain gage, 23-24, 45, 52-53, 130

N

Nipher shield, 28

Nonrecording rain gage, 22-25, 41, 52-53,

77-80, 130-131

Nonreset counter, 17, 74, 123-126

O

Odometer, electric, 125-126

Ohaus triple beam balance, 33, 137

One-mile contacts, 18

One-sixtieth mile contacts, 17-18

Operating instructions, weather instruments,

59-86

Orientation of wind vane, 51-52

Pins, anchor, 42-43, 142

Poles, anemometer, 41, 45-46

Portable electric fan psychrometer, 10-11,

65-66, 97-99

Portable fuel moisture scale, 32, 84-85, 136-137

Portable instrument shelter, 7-8

Portable wind meter, 20, 75, 121-122

Precipitation, 22-29

duration, 25, 28-29

instruments, 22-28

kind, 28-29

record, 28-29

Psychrometers, 9-10, 93-100

electric fan, 10, 40, 44, 65, 94-96

Forester 9X060, 95

Forest Service, 10-11, 95

handfan, 10-11,66, 96-97

Forester 9X050, 96

150
maintenance, 93-100

Mortarboard, 9, 13, 69, 99

operation, 63-69

portable electric fan, 10-11, 65-66, 97-98

Bendix Psychron, 11, 97

Gemware Electro V, 97

sling, 10-12, 66-67, 100

pocket, 12, 100

standard, 11-12, 100

Psychrometric tables, 9-10, 64

R

Rain gage, 22-28, 52-53, 77-82, 130-133

digital recording, 26

Farmer's, 25, 80, 130-131

fencepost, 25, 80, 130-131

Fergusson, 25-26, 52-53, 80-82, 132-133

Forest Service, 22-24, 45, 52, 77-79,

130-131

four-inch clear plastic, 24, 79, 130-131

installation, 52-53

maintenance, 130-133

measuring stick, 22-23,130

mounts, 23-24, 45, 52-53, 130

nonrecording, 22-25, 41, 52-53, 77-79,

130-131

operation, 77-82

recording, 22, 25-28, 41, 52-53, 80-82,

131-133

reliability, 27-28

shields, 26, 28, 53

small orifice, 22, 24-25, 79-80, 130-131

standard 8-inch, 22-23, 41, 52-53, 77-79,

130-131

tipping bucket, 27, 131

Weather Service type, 22-23, 130-131

wedge-shaped, 25, 80, 130-131

weighing, 25-26, 52-53, 80-82, 132-133

Range adjustment, 105-107

Region 6 scale, 31, 136

Relative humidity, 4, 9-15

average,9

and dewpoint tables, 9, 64

instruments, 9-15

maximum and minimum, 9

pen arm, 13-14, 104-107

Remote readout, 20, 50-51

Remote weather station, 56-57

Report, fire-weather station condition, 39,

140-141

Reset wind counter, 17, 73, 124

Retreater, 90

Rod, index, 5-6

Salt solutions, 107

Scale,

Appalachian, 31, 55, 83, 135-136

Chisholm, 31-32, 84, 136-137

Forester 9X100, 135-136

Forester 9X120, 136-137

fuel moisture, 31-33, 41, 55, 83-86

Harvard balance, 31, 33, 86, 137

Ohaus, 33, 137

pocket, 31-32, 84-85, 136

portable, 31-32, 84-85, 136-137

shelters, 31, 33, 41, 45, 55, 135, 144-145

triple beam, 31, 33, 85-86, 137

Williams, 31-32, 84-85, 136

Screen, fuel moisture, 45, 53-54

Screen, thermometer, 6-8, 40, 42-45

Separated thermometer column, 89-91

Shelters,

accessory, 50, 143

cotton region, 6-8, 40, 42-45

instrument, 6-8, 40, 42-44

portable, 7-8

scale, 31, 33, 41, 45, 55, 135, 144-145

Shields, rain gage, 28, 53

Spirit thermometer, 4

Six's thermometer, 6, 62, 91-92

Sling psychrometer, 10-12, 66-67, 100

pocket, 12, 100

standard, 11, 100

Small Airways anemometer, 17, 111-112

Bendix, Bendix Friez, and Instruments Corp.

models, 111-112

Small orifice rain gage, 22, 24-25, 130-131

Snow board, 29

Snow measurement, 28-29, 53, 77, 79

depth, 29, 79

water equivalent, 29, 77, 79

Snow stake, 29

Speed, wind, 16-20

Spinning bracket, 5, 40, 44, 91

Standard fire-weather station, 39-41

equipment, 40

location, 40

layout, 41

Standard maximum-minimum thermometers,

5, 40, 44, 91

151
Standard rain gage, 22-23, 41, 52-53, 77-79,

130-131

Standards, 39

Station, fire-weather, 40-58

automatic, 56-57

portable, 56

remote, 57

standard, 40-41

Stewart anemometer, 115-117

aluminum cup, 115-116

4-cup, 116-117

Stewart odometer, 125-126

Stewart wind direction system, 51-52, 127-129

Stick, fuel moisture, 30-31, 41, 53-54, 134

Stick, measuring, 22-23, 130

Support, instrument shelter, 42-43

Support, rain gage, 23-24, 45, 52-53, 130

Support, Townsend, 5, 40, 44, 91

System, wind, 51-52, 127-129

spirit, 4-5

standard maximum-minimum, 5, 40, 44, 61-62, 91

Support, Townsend, 5, 40, 44, 91

reading, 60

round bulb, 4-5

wet bulb, 10-13, 94

Thermoscreen, 6-8, 40, 42-45

Time of precipitation, 25, 28-29

Tipping bucket rain gage, 27, 131

Tool cache, 88

Totalizing anemometer, 18, 74, 117-118

Totalizing wind counter, 17-18, 41, 50-51,

73-74, 124-126

nonreset, 17, 74, 123-126

reset, 17, 73, 124

with 10-minute timer, 17-18, 73, 124

Tower, anemometer, 46

Townsend Support, 5, 40, 44, 91

Triple beam balance, 33, 85-86, 137

Twenty-foot standard, 16, 45-47, 75

Tables, psychrometric, 9-10

Temperature, 4-8

average, 4

current, 4-6

dewpoint, 9-10

dry bulb, 4, 9

instruments, 4-6

maximum, 4-6, 60-62

minimum, 4-6, 60-62

pen arm, 13-14, 104-105

wet bulb, 4, 9

Ten-minute wind counter, 17-18, 51, 73, 124

Thermometers, 4-6

alcohol, 4-5, 60, 89-90

Bourdon tube, 4, 13, 14

bimetal, 4, 13, 14

combined maximum-minimum, 6, 62, 91-92

cylindrical bulb, 4-5

deformation, 4, 13

dial, 4

dry bulb, 10-13, 94

fractured columns, 89-90

liquid-in-glass, 4-6

maintenance, 89-92

markings, 89

mercury-filled, 4-6, 60, 89-91

screen, 6-8

separated columns, 89-91

Six's maximum-minimum, 6, 62, 91-92

spinning brackets, 5, 40, 44, 91

Vanes, wind, 16, 20-21, 41, 45, 51-52, 127-129

Ventilation, wet bulb, 9-10, 63-64

Vertical clouds, 34-37

W

Water equivalent, 29, 77, 79

Weather Measure anemometers, 18, 120-121

Weather Measure hygrothermograph, 44, 101-107

Wedge-shaped rain gage, 25, 80, 130-131

Weighing rain gage, 25-26, 80-82, 132-133

Wet- and dry-bulb hygrometer, 9, 12, 68

Wet bulb,

depression, 9

temperature, 4, 9-10

thermometer, 10-13, 94

ventilation, 9-10, 63-64

wick, 9-10, 63-64, 93-94

Williams pocket scale, 31-32, 84-85, 136

Wind, 16-21

Wind counters, 16-19, 50-51, 73-76,123-126

Wind direction, 16, 21, 127-129

Wind direction indicator, 21, 41, 50-52, 127-129

Wind meter, hand-held, 20, 75, 121-122

Windspeed, 16-20, 73-122

Wind system, 20, 127-129

Wind vane, 16, 20-21, 45, 51-52, 127-129

Zero adjustment, 104-107

152
Ml ^4) "• ^- «DEPARTMENT OF COMMERCE

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICE

RELATIVE HUMIDITY

and

DEW POINT TABLE

Pressure 23 Inches of Mercury

For use at elevations between 6J01 and 8,500 feet above sea level

(in Alaska use at elevations between 5,701 and 7,900 feet above sea level)

Values in the body of the table are relative

humidities (in percent) and dew points (in deg. Fahr.), with

respect to water, for indicated values of wet and dry bulb

temperatures in degrees Fahrenheit.

HOW TO USE THE TABLE

Locate at the top of the column the reading corresponding to

the wet bulb temperature. Locate at the left side of the table

the reading corresponding to the dry bulb temperature. Follow

down the column under the wet bulb temperature, and across trom

the dry bulb temperature; at the intersection of these two

columns will be found the relative hximidity (%) in black and the

dew point (^F.) in red.

599-270 O - 76 - 12
WET BULB TEMPERATURES

9 10 11 12 1

13 114 15 16 17 18 19 20

15 -30

11

-13

?4 17

0

so

+5

64

9

77

13

91

16

?

-lb

14

-13 -5

19

+1

5?

6

65

10

7fl

14

9?

17 -44 -21

17

-10

79

-3

41

+3

54

8

66

12

79

15

97

18

-34n

-17

19

-8

11

-1

41

+5

55

9

67

13

SO

16

91

19 -28

10

-14

7?

-5

11

+1

45

6

57

10

69

14

«1

17

91

20 -531

-23

11

-11

?4

-3

Tí

+3

47

8

5?

12

79

15

?2

18

?4 21 22 23 24 25

21 -385

-18

16

-8

77

-1

17

+5

4R

9

60

13

71

17

82

20

94

22

-308-15

1»

-6

?9

+1

19

6

50

11

61

14

72

18

83

21

95

23

1

-24

11

-11

71

-3

11

+3

41

8

52

12

62

16

73

19

S4

22

95

24 -414

-19

14

-8

71

-1n

+5

41

9

51

13

64

17

74

20

85

23

96

25

-317

-15

Ifi

-5

?fi

+1

Ti

7

4'i

11 15 18

7Í

21

94

24

?6 26 27 28 29 30

26

1

-24

10

-11

19

-3

28

+3

37

8

47

13

56

16

66

20

76

23

86

25

97

27

-421

-19

1?

-8

?1

0

10

+5

19

10

48

14

58

18

67

21

77

24

87

26

97

28 -316

-14

15

-5

?1

+2

1?

7

41

12

50

16

59

19

69

22

7«

25 27

9«

29

-239

-10

17

-2

?5

+5

14

9

41

13

52

17

61

20

70

23

79

26

S9

29

9«

30

-40 -18

11

-7

l?

+1

28

6

36

11

44

15

53

19

«2

22

71

25

99

27

f)9

30

9? 31 32 33 34 35

31

-296-13

14

-4

??

+3

in

8

If

13

46

17

55

20

61

23

77

26

81

28

90

31

99

DRY BULB 32

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TEMPERATURES 33

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WET BULB TEMPERATURES

46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

81 -231

-53

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11

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84 -311

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86 -251

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87 -44 -122

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TEMPERATURES 107 -211

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WET BULB TEMPERATURES

31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

51 -48

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33

39

36

43

38

47

40

52

42

56

44

61

46

65

48

70

50

75

52

79

53

84

55

90

56

95

58

100

59 -20

3

-6

7

+3

10

9

14

15

17

19

21

23

25

26

28

29

32

32

36

35

40

37

44

39

48

42

52

44

57

46

61

48

66

49

70

51

75

53

80

54

85

56

90

58

95

59

100

60 -32

2

-12

5

-1

8

+6

12

12

15

17

18

21

22

25

26

28

29

31

33

34

37

36

41

39

45

41

49

43

53

45

57

47

62

49

66

50

71

52

75

54

80

55

85

57

90

59

95

60

100

61 62 63 64 65

61 -20

3

-6

6

+3

10

10

13

15

16

19

20

23

23

27

27

30

30

33

34

35

38

38

42

40

46

42

50

44

54

46

58

48

62

50

67

52

71

53

76

55

80

56

85

58

90

60

95

61

100

62 -32

2

-11

5

-1

8

+7

11

13

14

17

17

21

21

25

24

28

28

31

31

34

35

37

39

39

43

41

46

43

50

45

54

47

59

49

63

51

67

53

72

54

76

56

81

58

85

59

90

61

95

62

100

63 -19

3

-5

6

+4

9

10

12

15

15

20

19

24

22

27

25

30

29

33

32

36

36

38

40

40

43

43

47

45

51

47

55

49

59

50

63

52

68

54

72

55

76

57

81

59

85

60

90

62

95

63

100

64 -32

1

-11

4

0

7

+7

10

13

13

18

17

22

20

26

23

29

26

32

30

35

33

37

37

40

40

42

44

44

48

46

52

48

56

50

60

52

64

53

68

55

72

57

77

58

81

60

86

61

90

63

95

64

100

65 -19

3

-5

6

+4

9

11

12

16

15

20

18

24

21

28

24

31

27

34

31

36

34

39

38

41

41

43

45

45

49

47

52

49

56

51

60

53

64

54

68

56

73

58

77

59

81

61

86

62

90

64

95

65

100

66 67 68 69 70

ES

66 -31

1

-10

4

0

7

+8

10

14

13

18

16

22

19

26

22

29

25

32

28

35

32

38

35

40

39

42

42

44

46

46

49

48

53

50

57

52

61

54

65

55

69

57

73

59

77

60

82

62

86

63

91

65

95

66

100

67 -18

3

-4

6

+5

8

11

11

16

14

21

17

25

20

28

23

31

26

34

29

37

33

39

36

41

39

44

43

46

46

48

50

50

54

51

57

53

61

55

65

57

69

58

73

60

78

61

82

63

86

64

91

66

95

67

100

68 -29

1

-9

4

+1

7

8

10

14

12

19

11

23

18

27

21

30

24

33

27

36

30

38

33

41

37

43

40

45

44

47

47

49

51

51

54

53

58

54

62

56

66

58

70

59

74

61

78

62

82

64

86

65

91

67

95

68

100

69 -58 -16

3

-3

5

+5

8

12

11

17

13

21

16

25

19

29

22

32

25

35

28

37

31

40

34

42

38

44

41

46

44

48

48

50

51

52

55

54

58

56

62

57

66

59

70

60

74

62

78

63

82

65 li 68

95

69

100

70 -27 -8

4

+2

7

9

?

15 20

1?

24

1/

27

20

31

23

34

26

36

29

39

32

41

35

43

38

46

42

48

45

50

48

51

52

53

55 II a i! 7^0° n fi |2^ if 11 lí 70100

71 72 73 74 75

71 -50 -15

3

-2

5

+6

8

13

10

18

13

22

16

26

18

29

21

32

24

35

27

38

30

40

33

43

36

45

39

47

42

49

46

51

49

53

52

54

56

56

59

58

63

59

67

61

71

63

75

64

79

65

83

67

87

68

91

70

96

71

ion

DRY BULB

TEMPERATUR

72 -25

2

-7

4

+3

6

10

9

16

11

20

14

24

17

28

19

31

22

34

25

37

28

39

31

42

34

44

37

46

40

48

43

50

46

52

50

54

53

56

56

57

60

59

64

61

67

62

71

64

75

65

79

67

«3

68

87

69

91

71

96

72

ion

73 -43

1

-13

3

-1

5

+7

8

13

10

18

13

23

15

27

18

30

20

33

23

36

26

39

29

41

32

43

34

46

37

48

41

50

44

52

47

53

50

55

53

56

57

58

60

60

64

62

68

63

71

65

75

66

79

68

83

69

87

70

91

72

96

73

ion

74 -22

2

-6

4

+4

6

11

9

16

11

21

14

25

16

29

19

32

21

35

24

38

27

40

29

43

32

45

35

47

38

49

41

51

44

53

47

55

51

56

54

58

57

60

61

61

64

63

68

64

77

66

75

67

79

69

83

70

87

71

91

73

96

74

100

75 -37

1

-12 0

5

+8

7

14

10

19

12

24

1?

27

1?

31

20

34 37

?5

39

?8

42

JO

44

?3

46

36

48

3?

50

4S

52

45

54

4?

56

51

58

55

59

5?

61

51

62

Í5

64

Í8

65

72

67

76

68

SO

70

S,1

71

«7

72

V

74

ífi

75

ini)

76 77 78 79 80

76 -19

2

-4

4

+5

6

12

9

17

11

22

13

26

16

30

18

33

21

36

23

38

26

41

28

43

31

45

34

48

37

50

40

52

43

53

46

55

49

57

52

59

55

60

58

62

6?

63

65

65

69

66

7?

68

76

69

sn

71

84

72 73

9?

75

96

76

ino

77 -32

1

-10

3

+2

5

9

7

15

10

20

12

24

14

28

17

32

19

35

21

37

24

40

26

42

29

45

32

47

35

49

37

51

40

53

43

55

46

56

49

58

52

60

55

61

59

63

6?

65

66

66

69

68

73

69

76

70

«n

72

84

73

88

74

9?

76

96

77

inn

78 -17

2

-3

4

+6

6

13

8

18

11

23

13

27

15

30

17

33

20

36

22

39

25

42

27

44

30

46

33

48

35

50

38

52

41

54

44

56

47

58

50

59

53

61

56

63

59

64

63

66

66

67

69

69

73

70

76

71

80

73

84

74

88

75

V

77

96

78

100

79 -27

1

-8

3

+3

5

11

7

16

9

21

12

25

14

29

16

32

18

35

21

38

23

41

26

43

28

45

31

48

33

50

36

52

39

54

41

55

44

57

47

59

50

61

53

62

56

64

60

65

63

67

66

68

70

70

73

71

77

72

«0

74

84

75 76

9?

78

96

79

inn

80 -52 -14

2

-1

4

+8

6

14 19 24

U2.

28 31

-LL

34

19.

37

.22.

40

.2L

42 45

_¡9.

47 49 51

2?

53

.J9.

55

_Í2.

57 58 60

_¿.l,

62

,54

63 65

69

66 68

.M.

69

7?

71 72

77

73

_2L

75 76

92

79 80

1ÇC
WS TA B-.0-5B U. S. DEPARTMENT OF COMMERCE

(11-73) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICE

RELATIVE HUMIDITY

and

DEW POINT TABLE

Pressure 25 Inches of Mercury

For use at elevations between 3,901 and 6,100 feet above sea level

(in Alaska use at elevations between 3,601 and 5,700 feet above sea level)

Values in the body of the table are relative

humidities (in percent) and dew points (in deg. Fahr.), with

respect to water, for indicated values of wet and dry bulb

temperatures in degrees Fah renheit.

HOW TO USE THE TABLE

Locate at the top of the column the reading corresponding to

the wet bulb temperature. Locate at the left side of the table

the reading corresponding to the dry bulb temperature. Follow

down the coltamn under the wet bulb temperature, and across trom

the dry bulb temperature; at the intersection of these two

columns will be found the relative humidity (%) in black and the

dew point (®F.) in red.

599-270 O - 76 - 13
WET BULB TEMPERATURES

13 14 15 16 17 18 19 20 21 22 23 24 25

20 -V -2^0^ 3'2 ¿4^ 56^ ¿¿ sV ¡i

21 -ÍÍ -11

23

-3

34 4^

a

58 7^ ¿1 Í4°

22 -463

-20

14

-8

25

-1

36 ti 5^9° lí è! 9^

23 -346

-16

17 if í¿ 49' èi

a ¿1ë

24 -279

-12

19 3-¿ Îè 5? ¿í /í iS ^¿

25 -52 -21

12

-9

22

-1

12

+5

4?

10 Í3 14 18 21

85 .'è 26 27 28 29 30

26 -365

-16

14

-6

24

+1

34

7

44

12

54

16

65

19

75

22

S6

25

97

27 -27 -12

17 26

+4

36

9

46

13

56

17

66

21

76

24

87

26

97

28 -56 -21

10

-9

19

0

29

+6

18

11

48

15

57

19

67

22

77

25

87

27

9«

29 -374

-16

11

-5

22

+2

31

8

40

12

49

16

59

20

68

23

78

26

8«

29

9«

30 -277

-11

1;

-2

2^1

+4

33

10

42

14 18

fío

21

79

24

7f

27

í)9

30

ti 31 32 33 34 35

31 -541

-20

10

-8

IR

0

26

+6

15

11

44

16

5?

19

61

23

71

26

RO

28

90

31

99

32 -354

-15

12

-4

20

+3

28

9

37

13

45

17

54

21

61

24

72

27

81,

30

9Ç

32

100

33 -257

-10

15

-1

22

+5

30

u

39

15

47

19

56

22

64

25

71

28

87

31

91

33

100

34 -482

-189-6

17

+2

25

8

32

12

40

17

49

20

57

24

65

27

74

29

83

32

91

34

100

35 -314

-13

12 1I +4

27

10

34 ii iá

a l^ II lí ii láí 36 37 38 39 40

36 -227

-9

14

0

71

+7

79

u

16

44 \^

ü 6^^u 11 ^2^ 10^0^

37 -403

-169

-5

16 Í^ 1? tó kÍ l^ l\u ^l il íí ^<¡¿

38 -S' -11

1?

-1

19 îè il k^ í?w lí 11

n ^1 íf ,ín«

39 -^^ -197

-6

14n 2? \l 11 l\ \i l\ 7^8 7',' ¿í 9V 1,?,?

40 -32

"ift \'^V

MM ^^

^W^

n ?fl (?^ ^^ in'í 41 42 43 44 45

41 -'1 fF

U ?? \]M Ikw

u 4°

n T'Í íi íi

S

DRY BULB 42 -39? -'i -ú

n ^1W il 11 h' 5^R' (?Í h' ?9'

M ái

M

TEMPERATURES 43 -255

-9

in 16°

+1 ]l \l 21

41

24

47 Ii ?9°

U ?^ ii

E ^\M

44 -481

-177

-4

11

+4

18 il 1510

19

16

22

4?

25

48

28V, 31

60

34

66 i^ ¡fi ^6° ii irirt

45 -294

-100 +7

20

12

2^

17

31

20

37

24

41

27

4?

30 32

fil

35

67

37

71E

41

fifi ii Ifi^ 46 ¡ti 48 49 50

46 -196

-5

11 Í7^ 22 \^ 18

33

u

25

44 11 \ï ii ii ]l fo i^ 1^ lí)&

47 -323

-128-1

13 íiwM iï 2440 l\ fl

« J5 11 ]i ^l i^ %i Al

48 -205

-6

10

+2

15

9

20

14

25

18

10

22

15

25

41 II ¥2 ^5^7 1% il

nM í-i ^l lee

49 -352

-u72

12

+5

17

11

21

16

26

20

11

24

37

27

42 1? l\M ii fo ilw í) íi Ai

50 -224

-7?+2

13

8

19

14

21

18

2!)

22

13

25

3$

28

43

31

48 fi

w 11 Yo )\ \\

W ^\ ihl) 51 52 53 54 55

51 -39?

-146

-3

10

+5

15

11

20

16

24

20

29

24

34

27

39

30

44

33

49

35

54

37

60 ï% f^ 44

76 "à '.%

M 1^

52 -243

-88+1

12

8

17

n

71

18

26

22

30

25

15

28

40

31

45

34

50

36

55

39

60

41

66

43

71 77 82 "sa 94 roo

53 -451

-165-39+5

14

11

IR

16

22

20

77

24

12

27

36

30

41

33

46

35

51

38

56

40

61

42

66

44

72

46

77

48

81

50

88

51

94 lili.

54 -273

-97+1

11

8

15

13

19

18

24

22

78

25

33

29

37

31

42

34

47

37

52

39

57

41

62

43

67

45

72

47

77

49

83

51

89

M 100

55 -531

-17 -48+4

13

11

17

16

?1

20 24

29

27

34

30

38

33

43

36

4?

38n40 42

62 '67

46

73

48

7?

50

?3

52 V4 100
WET BULB TEMPERATURES

35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

56 -29?

-1060

10

+8

14

13

18

18

22

22

26

26

31

29

35

32

39

34

44

37

49

39

53

41

58

44

63

46

68

47

73

49

78

51

83

53

89

54

94 100

57 -184

-48+4

12

11

15

16

19

20

23

24

28

27

32

30

36

33

40

36

45

38

49

41

54

43

59

45

64

47

68

49

73

50

79

52

84

54

89

55

94

37

100

58 -31?

-106

01+7

13

13

17

18

21

22

25

26

29

29

33

32

37

35

41

37

46

40

50

42

55

44

59

46

64

48

69

50

74

51

79

53

84

55

89

56

95

58

100

59 -194

-57+4

11

11

14

16

18

20

22

24

26

28

30

31

34

34

38

36

42

39

47

41

51

43

55

45

60

47

65

49

69

51

74

53

79

54

84

56

89

57

95

59

100

60 -32?

-11509

+8

1?

13

16

18

_19

22 1 ?326

?7

29

31

32

35

35

39

38

43

40

47

42

52

44

56

46

61

48

65

50

70

52

75

54

79

55

84

57

90

58

95

60

100

61 62 63 64 65

61 -193

-57

+4

in

U

14

16

17

"""21

?1

24

74

28 31

32

34

36

37

40

39

44

41

48

43

52

46

57

48

61

49

66

....

70

53

75

55

80

56

85

58

90

59

95

61

100

62 -331

-1150s+8n

14

15

19

18

23 26

26

30

29

33

33

35

37

38

41

40

45

43

49-

45

53

47

57

49

62

51

66

52

71

54

75

56

80

57

85

59

90

61

95

62

100

63 -191

-56

+4911

13

16

16

21 25

23

28

77

31

30

34

34

37

38

39

42

42

46

44

50

46

54

48

58

50

62

52

67

54

71

55

76

57

80

58

85

60

90

62

95

63

100

64 -341

-114

0S+8

11

14

14

19

17

23

?1

27

74

30 33

31

36

35

38

39

41

43

43

46

45

50

47

54

49

59

51

61

53

67

55

72

56

76

58

81

60

85

61

90

63

95

64

100

65 -191

-4

fi

+5 11

1?

17

15

21

1''

25

??

29 32

p9

35 37

Iff

40 42

41

44

47

47 49 50 52

ff1

54

«S

56

72

57

76

59

»1

61

Si

62

90

64

9Í

65

100

66 67 68 69 70

66 -331

-104

+178

11

14

13

19

16

23

?n

27

?3

31 34

30

36

33

39

17

41

40

44

44

46

48

48

5?

50

56

52

60

53

64

55

68

57

72

58

77

60

81

62

86

63

90

65

95

66

100

67 -193

-46

+58

12

11

17

15

22

IS

26

71

29

?4

32

77

35

31

38

34

40

38

43

41

45

45

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41

10

44

11

47

12

49

13

52

15

54

16

57

17

59

19

61

20

63

22

65

23

67

25

68

26

70

28

72

29

73

31

75

33

77

34

78

36

80

38

81

40

82

42

84

44

85

46

112 -29 -41

+8?163234286327

368409

43

10

46

11

49

13

51

14

54

15

56

16

58

18

60

19

62

21

64

22

66

24

68

25

70

27

71

28

73

30

75

31

76

33

78

35

79

37

81

38

82

39

84

42

85

44

113 -101

+5?141214265

316

357

398

42

10

45U

48

12

51

13

53

14

55

16

58

17

60

18

62

20

64

21

66

23

68

24

69

26

71

27

73

29

74

30

76

32

77

34

79

35

80

37

82

39

83

41

85

114 -181

+12113

194255

306347

388419

44

10

47

11

50

12

53

14

55

15

57

16

59

17

61

19

63

20

65

22

67

23

69

24

71

26

72

27

74

29

76

31

77

32

79

34

80

36

82

37

83

39

85

41

115 -31 -41

+87173234

285336

377

40844947

11

49

12

52

13

54

14

57

15

59

17

61

18

63

19

65

21

67

22

69

23

70

25

72

26

74

28

75

_25.,

77

..3.1

78

33

80

34

81

36

83

3J.

84

116 -101

+57143

214275326

367398

439

46

10

49U51

12

54

13

56

15

58

16

60

17

62

18

64

20

66

21

68

23

70

24

72

25

73

27

75

28

77

30

78

31

80

33

81

35

83

36

84

DRY BULB 117 -181

+11127193254

305356

38742845948u51

12

53

13

55

14

58

15

60

16

62

18

64

19

66

20

68

22

70

23

71

24

73

26

75

27

76

29

78

30

79

32

81

33

82

35

84

JU.

TEMPERATURES 118 -31 -31

+92173

244295336

377

418

449

47

10

50

11

52

12

55

13

57

14

59

16

62

17

64

18

65

19

67

21

69

22

71

23

73

25

74

26

76

28

78

29

79

31

81

32

82

34

84

35

119 -9 +6 15 22 274

32 366407

438

469

49

12.

52

12

54

13

57

14

59

OS

61

16

63

17

65

19

67

20

69

21

71

22

72

24

74

25

76

27

77

28

79

.3_q,

80

_.3L

82

33

83
WS TA B-0-5C U. S. DEPARTMENT OF COMMERCE

(11.73) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICE

RELATIVE HUMIDITY

and

DEW POINT TABLE

Pressure 27 Inches of Mercury

For use at elevations between 1,900 and 3,900 feet above sea level

(in Alaska use at elevations between 1.700 and 3,600 feet above sea level)

Values in the body of the table are relative

humidities (in percent) and dew points (in deg. Fahr), with

respect to water, for indicated values of wet and dry bulb

temperatures in degrees Fahrenheit.

HOW TO USE THE TABLE

Locate at the top of the column the reading corresponding to

the wet bulb temperature. Locate at the left side of the table

the reading corresponding to the dry bulb temperature. Follow

down the column under the wet bulb temperature, and across from

the dry bulb temperature; at the intersection of these two

columns will be found the relative humidity (%) in black and the

dew point (®F.) in red.
WET BULB TEMPERATURES

20 21 22 23 24 25 26 27 28 29 30

30 -453

-17

12

-6

21

+2

30

8

39

13

49

17

58

21

68

24

78

27

89

30

99 31 32 33 34 35

31 -315

-13

14

-3

23

+5

32

10

41

15

50

19

60

22

69

25

79

28

89

31

99

32 -238

-8

17

0

25

+7

34

12

43

16

52

20

61

24

71

27

80

29

90

32

100

33 -43?

-16

11

-5

19

+3

27

9

36

14

45

18

54

22

63

25

72

28

81

31

91

33

100

34 -295

-12

13

-2

?1

+5

79

11

38

16

46

20

55

23

64

26

73

29

82

32

91

34

100

35 -21

ft

-7 +1

?1

8

11

13

40

17 21

?7

25

65

28

7*

30

??

33

91

35

100 36 37 38 39 40

36 -393

-15

1(1

-4

18

+4

26

10

33

15

42

19

50

23

58

26

66

29

75

31

83

34

91

36

100

37 -275

-10

13

0

20

+7

28

12

35

17

43

21

51

24

59

27

67

30

75

32

83

35

92

37

100

38 -571

-188

-6

15

+3

22

9

30

14

37

19

45

22

53

26

60

28

68

31

76

34

84

36

92

38

100

39 -331

-12

in

-2

17

+6

24

11

32

16

39

20

47

24

54

27

61

30

69

32

76

35

84

37

92

39

100

40 -236

-7

13

+2

19

8

26

14

34

18

41

22

48

25

55

28

62

31

69

33

77

36

84

38

92

40

100 41 42 43 44 45

41 -432

-158-3

15

*5

22

U

28

16

35

TO

42 49

26

56

29

63

32

70

34

77

37

85

39

92

41

100

42 -274

-9

11

0

17

8

24

13

30

18

37

21

43

25

50

28

57

31

64

33

71

36

78

38

85

40

92

42

100

43

1

-187-5

13

4

19

10

26

15

32

19

38

23

45

26

51

29

58 11 34

71

37

78

39

85

41

93

43

100

44 -323

-119-1

15

+7

21

12

27

17

33

21

39

24

46

28

52

30

59

33

65

36

72

38

79

40

86

42

93

44

100

45 -215

-6

11

+3

17

9

23

14

29

19

35

23

41

26

47

29

53

32

59

34

66

37

72

39

79

41

86

43

93

45

100

46 47 48 49 50

pv r^ %y r\1 11 r\

46 -382

-138

-2

13

+6

19

12

25

16

30

21

36

24

42

27

48

30

54

33

60

36

67

38

73

40

80

42

86

44

93

46

100

UKT DULD

TEMPERATURES

47 -244

-7

10

+2

15

9

21

14

26

18

32

22

37

26

43

29

49

32

55

34

61

37

67

39

74 ¡l 43

87

45

93

47

100

48 -461

-156

-3

12

+5

17

U

22

16

28

20

33

24

39

27

44

30

50

33

56

36

62

38

68

40

74

42

80

44

87

46

93

48

100

49 -263

-98+1

13

8

18

13

24

18

29

22

34

26

40

29

45

32

51

34

57

37

63

39

68

41

75

43

81

45

87

47

93

49

100

50 -571

-175

-4

10

+4

15

11

20

16

25

20

30

24

36

27

41

30

46

33

52

36

57

38

63

40

69

42

75

44

81

46

87

48

94

50

100

51 52 53 54 55

51 -31?

-u7

0

17

+7

17

13

22

18

27

22

32

26

37

29

42

32

47

34

53

37

58

39

64

41

70

44

75

46

81

47

88

49

94

il

100

52 -204

-59+4

14

10

18

15

23

20

28

24

33

27

38

30

43

33

48

36

54

38

59

40

65

43

70

45

76

47

82

48

88

50

94

52

100

53 -36?

-126-1

11

+7

15

13

20

18

24

22

29

25

34

29

39

32

44

34

49

37

54,

39

60

42

65

44

71

46

76

48

82

50

88

51

94

53

100

54 -224

-6R+3

17

10

17

15

21

20

?6

24

30

27

35

30

40

33

45

36

50

38

55

41

60

43

66

45

71

47

77

49

82

51

88

52

94

54

100

- 55 -42 -145

-29+6

14

12

18

17

23

22

27

25

32

29

36

32

41

35

46

37

51

40

56

42

61

44

66

46

72

48

77

50

83

52

88

53

94

55

100

56 57 58 59 60

56 -253

-77

+2

11

9

15

15

20

20

24

24

28

27

33

30

37

33

42

36

47

39

52

41

57

43

62

45

67

47

72

49

78

51

83

53

89

54

94

56

100

57 -501

-155

-29*6

13

12

17

17

21

22

25

26

30

29

34

32

39

35

43

37

48

40

53

42

57

44

62

46

67

48

73

50

78

52

83

54

89

55

94

57

100

58 -272

-86+2

10

9

14

15

18

20

22

24

26

27

31

31

35'

34

40

36

44

39

49

41

53

43

58

46

63

48

68

49

73

51

78

53

84

55

89

56

94

58

100

59 -164

-38+6

12

12

16

17

20

22

24

26

28

29

32

32

36

35

41

38

45

40

50

42

54

45

59

47

64

49

69

51

73

52

79

54

84

56

89

57

94

59

100

60 -292

-96

+29

9

13

15

17

ZO

21

24

25

28

29

31 34 37 39

_4i

41 44

5?

46

59

48

^4

50 52

7*

53

79

55

84

57

89

58

?5

60

100
WET BULB TEMPERATURES

39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

61

4 ~\11 14 18 72 76 30 34 38 47 47 51 56 60 65 69 74 79 84 89 95 100

62

7 ) 9 12 16 20 73 77 31 35 39 43 48 5? 56 6! 65 70 75 80 85 90 95 100

63

3 7 10 14 17 21 25 28 3? 36 40 44 48 53 57 61 66 70 75 80 85 90 95 100

64 S S 11 i'i Ifl ?? 76 79 33 37 41 45 49 53 57 62 66 71 75 SO 85 90 95 100

65

.} 6 9 13 16 20 23 27 30 34 38 42 46 50 54 58 62 67 71 76 80 85 90 95 100

66 67 68 69 70

66 4 « u 14 17 21 24 28 31 35 39 43 47 51 55 59 63 67 72 76 81 85 90 95 100

67 6 <) 17 15 19 22 25 29 32 36 40 43 47 51 55 ?? 63 68 72 76 81 86 90 95 100

68 "4 *; 10 13

51

17 20 23

VI

30 33 41 44 48 52 56 60 64 68 72 77 81 86 90 95

6Ö

100

Ó9 "'', 'I 9 12 15 18 21 24 27 31 34 38 41 45 49 53 56 60 64 69 73 77 81 86 91 95 100

70 i 4 7 10 13 16 19 22 25 28 32 35 39 42 46 49 53 57 61 65 69 73 77 82 86 91 95 100

71 72 73 74 75

71

1

'\

8 11 14 17 30 23 26 29 33 36 39 43 46 50 54 58 61 65 69 73 78 82 86 91 95 100

72 4 9 15 18 71 74 27 30 34 37 40 44 47 51 54 53 62 66 70 74 78 82 86 91 95 100

73 3 5 8

1 <

11 13 16 19 22 25 28 31 ^^ 38 41 44 48 51 55 59 62 66 70 74 78 82 87 91 95 100

74

. 4 6 9 17 14 17 20 23 26 29 32 35 38 42 45 48 52 55 59 63 67 70 74 78 83 87

71

91 95 100

75 3 5 8 10 13 16 18 21 24 27 30 33 36 39 42 46 49 52 56 60 63 67 71 75 79 83 87 91 96 100 76 77 78 79 80

76 '1 4 6 9 11 14 17 19 77 75 28 31 34 37 40 43 46 50 53 57 60 64 67 71 75 79 83 87 91 96 100

77

-J-.

3 '> 7 10 12 15 18 20 23 26 29 32 34 37 41 44 47 50 54 57 61 64 68 71 75 79 83 87 91 96 100

78

1 4 6 9 11 13 16 19 21 24 27 29 32 35 38 41 44 48 51 54 57 61 64 68 72 76 79 83 87 91 96 100

79

5 7

}^ 12 14 17 20 22 25 27 30 33 36 39 42 45 48 51 55 58 61 65 68 72 76 80 84 88 92 96 100

80

,2 4 ,6 ,8 11 ^? 15 f? 20 23 26 28 ^} ^^f ^^ 40 43 46 49

^1^

55 58 62 65 69 72 76 ^^ 84 88 92 96 100 81 82 83 84 85

81 1 5 7 9 17 14 16 19 21 24 26 29 32 35 37 40 43 46 49 52 56 59 62 66 69 73 76 80 84 88 97 96 100

TEMPERATURES

82

-1/

2 4 6 8 10 13 15 17 20 22 25 27 30 35 38 41

58

44 47 50 53 56 59 63 66 69

¡1

73 77 80 84 aa 97 96 100

83 9 11 14 16 18 21 23 26 28 31 33 36 39 42 44 47 50 53 57 60 63 66 70 73 77 80 84 Sfi 97 96 100

84

2

+ 1

4

LÜ

,8 10 12 15 17 19 21 24 26 29 31 34 37 39 42 45 48 51 54 57 60 63 67 70 74 77 81 84 88 92 96 100

85 1 3 5 7 9 11 13 15 18 20 22 25 27 30 32 35 37 40 43 46 48 51 54 57 61 64 67 70 74 77 81 85 88 92 96 100

86 87 88 89 90

86

2 4 6 8 10 12 14 16 19 21 23 25 28 30 33 35 38 41 43 46 49 52 55 58 61 64 67 71 74 78 81 85 aa 97 96 100

37

5 7 9 11 13 15 17 19 22 24 26 29 31

55

33

5>

36

59

39 41 44 47 49 52 55

n

58

72

61 64

-7T

68

-IT

71 74 78 81 85 88 97 96 100

38

-y<

,2 4 6 8 10 12 !t 16 Í? 20 22 25 27 29 32 34 37 39 42 44 47 50 53 56 59 62 65 68 71 75 78 81 85 89 92 96 100

89

1 3 i 7 9 11 13 15 17 19 21 23 25 28 30 32 35 37 40 42 45 48 50 53 56 59 67 65 68 71 75 78 82 85 89 9? 96 100

90

1 2 4 6 8 10 12 13 15 17 20 22 24 26 , 28 31 33 35 38 40 43 45 48 51 54 56 _59_ 62 65 69 72 75 78 82 J5. 89 1 92

5T

96

-9Tr

100
WET BULB TEMPERATURES

53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

91 -13

2

+2

3

11

5

18

7

23

9

28

U

32

12

36

14

39

16

42

18

45

20

47

22

50

25

52

?7

54

?9

56

H

58

34

60

3Í

62

38

64

41

66

43

67

4fi

69

49

71 72 74

57

75

fJO

77 78

66

79

69

81

73

82

75

83

79

85

83

86

85

87

89

89

93

90

96

92 -23

1

-3

3

+8

4

16

6

22

8

27

10

31

11

35

13

38

15

41

17

44

19

47

21

49

23

51

25

54

27

56

30

58

32

60

34

62

36

63

39

65

41

67

44

69

46

70

49

72 73

54

75

57

76

60

78

63

79

66

80

69

82

72

83

75

84

79

86

S?

87

86

88

89

90

93

93 -45 -9

2

+4

3

13

5

19

7

25

9

29

10

33

12

37

14

40

16

43

18

46

20

48

22

51

24

53

26

55

28

57

30

59

32

61

35

63

37

65

39

66

42

68

¿(4

70

47

71

^0

73 74 76 1 77

58 1 60

79

63

80

66

81

69

83

73

84

76

85

79

87

82

88

86

89

89

94 -17

1

0

3

+10

4

17

6

23

8

28

9

32

U

36

13

39

15

42

17

45

19

47

20

50

22

52

24

54

27

57

29

59

31

61

33

62

35

64

38

66

40

68

42

69

45

71

47

72 Tit 76

}•>

77

58

78

61

80

64

81

67

83

70

84

73

85

76

87

79

88

82

39

86

95 -31

1

-5

2

+6

4

15

5

21

7

26

9

30

10

34

12

38

14

41

16

44

17

47

19

49

21

52

23

54

25

56

27

58

29

60

31

62

34

64

36

66

38

67

40

69

43

71

4?

72

4§

74 75 77

f.6

78

?8

80

61

81

64

82

67

84

70

85

73

86

76

88

79

89

83

96 -12

1

+3

3

12

4

19

6

24

8

29

9

33

11

37

13

40

14

43

16

46

18

48

20

51

22

53

24

55

26

57

28

59

30

61

32

63

34

65

36

67

39

68

41

70

43

72

^6

73

48

75

51

76

53

78

56

79

59

81

61

82

64

83

67

85

70

86

71

87

76

89

79

97 -23 -2

2

+9

4

16

5

22

7

27

8

32

10

36

12

39

13

42

15

45

17

48

19

50

21

52

23

55

24

57

26

59

28

61

30

63

33

65

35

66

37

68

39

70

41

71

44

73

46

74

49

76

51

77

54

79

56

80

59

82

62

83

65

84

67

86

70

87

71

88

76

98 -44 -8

2

+5

3

14

5

20

6

26

8

30

9

34

11

38

13

41

14

44

16

47

18

49

19

52

21

54

23

56

25

58

27

60

29

62

31

64

33

66

35

68

37

69

40

71

4?

73

44

74

47

76

49

77

57

79

''4

80

57

81

59

33

6?

84

65

85

68

87

71

88

74

99 -16

1

+1

2

11

4

18

5

24

7

29

8

33

10

37

12

40

13

43

15

46

17

49

18

51

20

53

22

56

24

58

26

60

28

62

30

64

32

65

34

67

36

69

3Í?

71

40

72

4?

74

4'í

75

47

77

50

78

5?

80

55

81

57

83

60

84

6?

85

65

87

68

88

71

100 -29

1

-4

2

+8 16

5

22

6

27

8

32

9

35

u

39

12

42

14

45

16

48

17

50

;9

53

21

55

23

57 59

?6

61

?8

63

30

65

33

67

34

68

35

70

IS

72

41

73

43

75

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71

79

74

80

78

81

81

83

85

84

88

85

92

87

96

88

100

89

-191-13+105177239

28

11

32

13

36

15

39

17

42

19

45

22

48

24

50

26

52

29

55

31

57

34

59

36

61

39

62

41

64

44

66

47

68

50

69

52

71

55

72

58

74

61

76

65

//

68

78

71

80

74

81

73

83

81

84

85

85

88

86

92

88

96

89

100

90 -37 -72

+64

146

218

26

10

30

12

34

14

38

16

41

18

44

20

47

22

49

25

52

27

54

29

56

32

58

34

60

.M.

62

39

64

42

66

45

67

47

69

50

71

53

72

56

74

59

75

62

77

65

78

68

79 81 82

78

84

32

85

85

86

89

87

92

89

96

90

100
WET BULB TEMPERATURES

54 55 56 57 58 59 50 61 62 53 64 65 66 67 68 59 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 85 87 88 89 90 91 92 93 94 95

91 -15

1

+ i

3

U

5

18

7

24

9

29

U

33

13

il

15

40

17

43

19

45

21

48

23

51

25

53

28

55

30

57

32

59

35

61

37

53

40

65

42

57

45

58

48

7Ô

51

72

53

73

56

75

59

'75

52

-78

55

1?

68

81

72

82

75

83

78

85

82

85

85

87

89

88

9?

90

96

91

100

92 -28

1

-4

2

+8

.4

16

6

22

8

2/

10

31

12

35

14

39

16

42

18

45

20

47

22

50

24

52

26

55

28

57

31

59

33

61

35

53

38

55

40

56

43

68

45

70

48

71

51

73

54

74

57

76

60

77

53

79

66

80

69

82

72

83

75

84

78

86

82

87

85

88

89

90

97

91

96

92

100

93 -11

2

+4

3

13

5

20

7

25

9

30

11

34

12

38

14

41

16

44

18

47

20

49

23

52

25

54

27

56

29

58

31

50

34

62

36

64

38

66

41

68

43

59

45

71

49

72

51

74

54

75

57

77

60

78

53

80

66

81

59

83

72

84

75

85

79

87

8?

88

85

89

89

91

93

92

96

93

100

94 -21

1

-1

3

+ 10

4

17

6

23

8

28

10

32

11

35

13

40

15

43

17

46

19

48

21

51

23

53

25

55

28

58

30

50

32

52

34

63

37

65

39

57

41

69

44

70

47

72

49

74

52

75

55

77

57

78

60

80

63

81

66

82

59

84

72

85

75

85

79

88

8?

89

85

90

89

92

93

93

96

94

100

95 -4J +6 14

. 5

21

7

26

9

31

10

35

12

39

14

42

15

45

18

47

20

50

22

52

24

55

26

57

28

59

30

51

33

53

35

65

37

57

40

68

42

70

45

72

47

73

50

75

52

76

55

78

58.

79

61

81

64

82

66

83 85

73

85

76

87

79

89

8?

90

86

91

89

93

91

94

96

95

100

96 -16

1

+ 1

3

11

4

19

6

25

8

29

9

34

11

37

13

41

15

44

17

47

19

49

21

52

23

54

25

56

27

58

29

60

31

52

33

64

35

56

38

58

40

70

43

71

45

73

48

74

50

75

53

77

55

79

58

80

61

82

64

83

67

85

70

86

73

87

76

88

79

90

8?

91

86

92

89

94

91

95

95

97 -30

1

-4

2

+8

4

16

5

23

7

28

9

32

10

36

12

40

14

43

15

45

17

48

19

51

21

53

23

56

25

58

27

50

29

62

32

64

34

66

35

57

38

69

41

71

43

72

45

74

48

76

51

77

53

79

56

80

59

81

61

83

64

84

57

86

70

87

73

88

76

90

79

91

81

92

85

93

89

95

93

98 -11

1

+4

3

13

5

20

6

26

8

31

9

35

11

38

13

42

15

45

15

48

18

50

20

53

22

55

24

57

26

59

28

51

30

63

32

65

34

67

37

69

39

70

41

72

44

74

46

75

48

77

51

78

54

80

56

81

59

83

6?

84

64

85

67

87

70

88

73

89

76

91

80

92

81

93

86

94

89

99 -21

1

-1

2

+ 10

4

18

5

24

7

29

9

33

10

37

12

41

14

44

15

47

17

49

19

52 54

23

57

25

59

27

51

29

63

31

65

33

65

35

58

37

70

39

72

42

73

44

75

46

76

49

>8

51

79

54

81

57

82

59

84

6?

85

55

86

68

88

71

89

74

90

77

92

80

93

81

94

86

lool -43 -/ + 7 15

5

22 27 32 36

U

40 43

14

46 49 51

29

54

21

55

23

58

2'?

60

27

62

29

64

31

66

33

68

3,'?

70

3f

71

4P

73

42

74

44

76

47

78

49

79

52

81

54

82

57

83

50

85

62

85

65

87

68

89

71

90

74

91

77

93

fio

94

83

101 -15

1

+2

3

12

4

20

5

25

7

30

8

35

10

38

12

42

13

45

15

48

17

50

18

53

20

55

22

57

24

60

26

62

28

64

30

65

32

67

34

69

36

71

38

72

40

74

43

76

45

77

47

79

50

80

52

82

55

83

57

84

50

85

63

87

65

89

68

90

71

91

74

92

77

94

80

102 -28

1

-3

2

+9

3

17

5

24

5

29

8

33

9

37

11

41

12

44

14

47

16

50

17

52

19

55

21

57

23

59

25

61

26

63

28

65

30

57

32

59

34

70

36

72

39

74

41

75

43

77

45

78

48

80

50

81

53

83

55

84

58

86

50

87

63

88

56

90

68

91

71

92

74

93

77

103 -10

1

+5

3

15

4

21

5

27

7

32

8

35

10

40

12

43

13

45

15

49

16

51

18

54

20

55

21

58

23

50

25

63

27

64

29

66

31

68

33

70

35

72

37

73

39

75

41

75

43

78

46

80

48

81

50

82

53

84

55

85

58

87

60

88

63

89

65

91

69

92

71

93

74

104 -19

1

+ 1

2

12

3

19

5

25

6

30

8

35

9

38

u

42

12

45

14

48

15

51

17

53

19

55

20

58

22

60

24

52

26

54

28

66

29

58

31

59

33

71

35

73

37

75

40

75

42

78

44

79

46

81

48

82

51

84

53

85

56

86

58

88

51

89

63

90

55

92

59

93

77

105 -37 -5 +8

3

17

4

23

6

29

7

33

8

37 41

11

44

13

47

14

50

16

52

18

55

19

57

?1

59

23

51

24

63

25

65

28

67

30

69

32

71

34

72

36

74

38

76

40

77

^2,

79

44

80

47

82

49

83

51

85

54

85

56

87

59

89

61

90

64

91

66

93

59

106 -12

1

+4

2

14

4

21

5

27

6

32

8

36

9

40

11

43

12

46

14

49

15

52

17

54

18

56

20

59

22

51

23

53

25

65

27

67

29

69

30

70

32

72

34

74

36

75

38

77

40

79

43

80

45

82

47

83

49

84

57

86

54

87

56

89

59

90

61

91

54

93

67

107 -23

1

-1 +11

3

19

4

25

6

30

7

35

8

38

10

42

11

45

13

48

14

51

16

53

17

55

19

58

20

60

22

62

24

54

26

56

27

68

29

70

31

72

33

73

35

75

37

77

39

78

41

80

43

81

45

83

47

84

50

86

57

87

54

88

57

90

59

91

6?

92

64

108 -49 -7

1

+7 16

4

23

5

29 33

8

37

9

41

10

44

12

47

13

50

15

53

15

55

18

57

19

50

21

62

23

64

24

66

26

68

28

70

30

71

31

73

31

75

35

76

37

78

39

79

41

81

43

82

46

84

48

85

50

87

5?

88

55

89

57

91

59

92

6?

109 -15

1

+3

2

13

3

21

5

27

5

32

7

35

8

40

10

43

U

46

13

49

14

52

15

54

17

57

18

59

20

51

22

53

23

65

25

67

27

69

78

71

30

73

3?

74

34

76

35

78

38

79

40

81

4?

' 82

44

84

46

85

48

86

50

88

53

89

55

91

57

92

50

110 -28 -2 +10 19

4,

25

5

30

6

35

?

39 42

1,0

45

M

48

1?

51

15

54

16

56

18

58

19

61

21

63

22

65

24

67

25

69

27

70

29

72

31

74

32

76

34

77

36

79

38

80

40

82

42

83

44

85

46

86

48

88

51

89

51

90

55

92

58

111 -8

1

+7

2

16

3

23

5

29

5

33

7

37

8

41

10

44

11

48

12

50

14

53

15

56

17

58

18

50

20

62

21

64

23

66

24

68

26

70

28

72

29

73

31

75

33

77

35

78

37

80

39

81

41

83

43

84

45

86

47

87

49

89

51

90

51

91

55

112 -17

1

+2

I

13

3

21

4

27

5

32

7

36

8

40

9

43

10

47

12

50

13

52

14

55

16

57

17

60

19

62

20

64

22

66

23

58

25

70

26

71

28

73

30

75

32

76

33

78

35

80

37

81

39

83

41

84

43

86

45

87

47

88

49

90

51

91

54

113 -32 -3

1

+10

I

18

4

25

5

30

5

35

7

39

8

42

10

46

11

49

12

52

14

54

15

57

16

59

18

61

19

63

21

65

22

67

24

69

25

71

27

73

29

74

30

76

32

78

34

79

36

81

37

82

39

84

41

85

43

87

45

88

47

90

50

91

52

114 -10 +6

2

15

3

23

4

29

5

33

7

38

8

41

9

45

10

48

11

51

13

53

14

56

15

58

17

61

18

53

20

65

21

67

23

69

24

71

26

72

27

74

29

76

31

77

32

79

34

81

35

82

38

84

40

85

42

86

44

88

45

89

48

91

50

115 -19 +2

..JL

13

_2

21

4

27

5

32

6

36

7

40

?

44

10

47

u

50 53

13

55

15

58

16

60

17

62

19

64

20

65

22

68 70

25

72

26

74

28

75

30

77

31

79

33

80

35

82

36

83

38

85

40

85

47

88

44

89

46

90

48

DRY BULB m -3

\

+10

2

18

3

25

4

30

6

35

7

39

8

43

9

45

10

49

11

52

13

55

14

57

15

59

17

62

18

64

19

55

21

68

22

70

24

71

25

73

27

75

28

77

30

78

37

80

33

81

35

83

37

84

19

86

41

87

4?

89

44

90

TEMPERA TURES 117 -10 +6

2

16

3

23

4

29

5

34

5

38 42

8

45

10

48

U

51

12

54

13

56

14

59

16

61

17

63

18

65

20

67

21

59

23

71

24

73

26

75

77

76

79

78

30

80

37

81

34

83 84

17

85

39

87

41

89

41

90

45

118 -20

1

+2

1

13

2

21

3

27

5

32

6

37

7

41

8

44

9

47

10

50

11

53

12

56

14

58

15

60

16

63

18

65

19

67

20

69

22

71

23

72

25

74

26

76

28

78

29

79

31

81

33

82

34

84

15

85

38

87

19

88

41

90

43

119 -40 -4

_.l

+10 19 25 31

—5.

35 40

-2.

43

-a.

47

_2L

50

-11

52 55 58

14

60

-15.

62

-IS

56

19

68

-21

70

..22

72

24

74

,2¿

75

27

77

2?

79

-20.

80

31

82

33

84

35

85

36

87

38

88

40

89
WS TA B-0-5D U. S. DEPARTMENT OF COMMERCE

(10-73) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICE

RELATIVE HUMIDITY

and

DEW POINT TABLE

Pressure 29 Inches of Mercury

For use at elevations between 501 and 1,900 feet above sea level

(in Alaska use at elevations between 301 and 1,700 feet above sea level)

Values in the body of the table are relative

humidities (in percent) and dew points (in deg. Fahr.), with

respect to water, for indicated values of wet and dry bulb

temperatures in degrees Fahrenheit.

HOW TO USE THE TABLE

Locate at the top of the column the reading corresponding to

the wet bulb temperature. Locate at the left side of the table

the reading corresponding to the dry bulb temperature. Follow

down the column under the wet bulb temperature, and across from

the dry bulb temperature; at the Intersection of these two

coltimns will be found the relative humidity (%) in black and the

dew point (^F.) in red.
WET BULB TEMPERATURES

21 22 23 24 25 26 27 28 29 30

JO

3 1'

—tr

27 37

-TÎ

46 57

Tí'

67

2i

77

27

88

30

99

31 32 33 34 35

31

1 10 20 29

—?

38

IT

48

TT

58 68 78 89

31

99

32 -364

-13

13

-3

22

+5

31

11

40

15

50

20

60

23

69

26

79

29

90

32

100

33 -257

-9

15

0

24

+7

33

13

42

17

52

21

61

25

71

28

80

30

90

33

100

34 -561

-189-5

18

+3

26

9

35

14

44

19

53

23

62

26

72

29

81

32

91

34

100

35 -344

-13

12

-2

20

+6

29

11

37

16

46

20

55

24

64

27

73

30

82

33

91

35

100 36 37 38 39 40

36 -246

-8

14

+1

22

8

31

14

39

18

48

22

56

25

65

28

74

31

82

34

91

36

100

37 -501

-179

-4

17

+4

25

10

33

15

41

20

49

24

58

27

66

30

74

32

83

35

91

37

100

38 -314

-11

11

0

19

+7

27

13

35

17

43

21

51

25

59

28

67

31

75

33

83

36

91

38

100

39 -217

-6

14

+3

21

9

29

15

37

19

44

23

52

26

60

29

67

32

75

34

83

37

92

39

100

40 -422

-149-2

16

+6

23

12

31

17

38

21

46

24

53

28

61

30

68

33

76

36

84

38

92

40

100 41 42 43 44 45

41 -265

-9

11

+1

18

8

26

14

33

18

40

22

47

26

54

29

61

32

69

34

77

37

84

39

92

41

100

42 -187

-4

14

+5

21

11

28

16

34

20

41

24

48

27

55

30

62

33

70

35

77

38

85

40

92

42

100

43 -333

-119

0

16

+8

23

13

29

18

36

22

42

25

49

28

56

31

63

34

70

36

78

39

85

41

92

43

100

44 -215

-6

12

+3

18

10

24

15

31

20

37

23

44

27

50

30

57

33

64

35

71

38

78

40

83

42

93

44

100

45 •422

-138-1

14

+6

20

12

26

17

32

21

39

25

Í5

28

51

31

58

34

65

36

72

39

78

41

86

43

93

45

100

46 47 48 49 50

46 -254

-7

10

+2

16

9

??

14

28

19

34

23

40

26

46

30

52

32

59

35

65

38

72

40

79

42

86

44

93

46

100

DRY BULB 47 -561

-166-3

1?

+5

18

11

21

17

29

21

35

25

41

28

47

31

53

34

60

36

66

39

73

41

79

43

86

45

93

47

100

TEMPERATURES 48 -293

-10B

+1

14

8

19

14

25

19

31

23

36

26

42

29

48

32

54

35

60

38

67

40

73

42

80

44

86

46

93

48

100

49 -195

-5

10

1^

16

11

21

16

26

20

32

24

38

28

43

31

49

34

55

36

61

39

67

41

74

43

80

45

87

47

93

49

100

50 -372

-12 , 7

-1

12

+7

17

13

22

18

28

22

33

26

39

29

44

32

50

35

56

38

62

40

68

A2

74

44

80

46

87

48

93

50

100

51 52 53 54 55

51 234

-69

+3

14

10

19

15

24

20

29

24

35

28

40

31

46

34

51

36

57

39

63

41

69

43

75

45

81

47

87

49

93

51

100

52 471

-146-2

11

-^6

15

13

20

18

25

22

31

26

36

29

41

32

47

35

52

38

58

40

63

42

69

44

75

46

81

48

87

50

94

52

100

53 -273

-87+2

12

9

17

15

22

20

27

24

32

27

37

31

42

34

48

36

53

39

58

41

64

43

70

46

76

48

82

49

88

51

94

53

100

54 -175

-39

+6

14

12

19

17

23

22

28

26

33

29

38

32

43

35

49

38

54

40

59

42

65

45

70

47

76

49

82

50

88

52

94

54

100

55 -322

-106-Hn9

15

15

20

20

25

24

30

27

34

31

39

34

44

36

49

39

55

41

60

44

65

46

71

48

76

50

82

52

88

53

94

55

100

56 57 58 59 60

56

—4-48f5n12

17

17

?1

22

?6

26

31

^l9

3ft

32

40

35

45

38

50

40

55

43

61

45

66

47

71

49

77

51

S2

53

88

54

94

56

100

57 -371

-116n

10

8

14

14

18

19

73

24

77

27

12

31

17

34

41

37

46

39

51

42

56

44

61

46

67

48n50

77

52

93

54

88

55

94

57

100

58 -213

-57

+5

11

11

16

17

20

22

24

26

29

29

33

32

38

35

42

38

47

40

52

43

57

45

62

47

67

49

72

51

78

53

83

55

89

56

94

58

100

59 -431

-12509

^8n

14

17

19

71

24

?5

28

10

31

14

34

19

37

41

39

40

42

51

44

5«

4b

fil

48

68

50

73

52

78

54

S3

56

89

57

94

59

100

60 -24 -6

L_i

+4

-lu.

11 17

JA

22

.21

26

-2Z,

29 33 36 38 41

.M

43 45 47 49

JiS.

51 53

JS.

55

.M.

57 58

,S4.

60

m.
WS TA B-0-5E U. S. DEPARTMENT OF COMMERCE

(lt-73) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICE

RELATIVE HUMIDITY

and

DEW POINT TABLE

Pressure 30 Inches of Mercury

For use at elevations between 0 and 500 feet above sea level

(in Alaska use at elevations between 0 and 300 feet above sea level)

Values in the body of tfie table are relative

humidities (in percent) and dew points (in deg. Fahr.), with

respect to water, for indicated values of wet and dry bulb

temperatures in degrees Fahrenheit.

HOW TO USE THE TABLE

Locate at the top of the column the reading corresponding to

the wet bulb temperature. Locate at the left side of the table

the reading corresponding to the dry bulb temperature. Follow

down the column under the wet bulb temperature, and across trom

the dry bulb temperature; at the intersection of these two

columns will be found the relative humidity (%) in black and the

dew point (®F.) in red.
WET BULB TEMPERATURES

21 22 23 24 25 26 27 28 29 30

30 -316

-12

15

-1

25

+6

35

11

45

16

56

20

66

24

77

27

88

30

99 31 32 33 34 35

31 -238

-8

18

+1

27

8

37

13

47

18

57

22

68

25

78

28

89

31

99

32 -482

-16U-4

20

+4

30

10

39

15

49

19

59

23

69

26

79

29

89

32

100

33 -315

-12

14

-1

23

+6

32

12

41

17

51

21

60

24

70

28

80

30

90

33

100

34 -228

-7

16

+2

25

9

34

14

43

18

52

22

62

26

71

29

81

32

90

34

100

35 -472

-16

10

-4

19

+5

27

U

36

16

45

20

54

24

63

27

72

30

81

33

91

35

100

36 37 38 39 40

36 -305

-U

11

0

71

+7

29

13

38

18

47

22l

55

"25

64

28

73

31

82

34

91

36

100

37 -217

-6

15

+3

23

9

31

15

40

19

48

23

57

26

65

29

74

32

32

35

91

37

100

38 -422

-14

10

-2

13

+6

25

12

33

17

42

21

50

25

58

28

66

31

74

33

83

36

91

38

100

39 -275

-9

12

+1

20

8

23

14

35

19

43

22

51

26

59

29

67

32

75

34

83

37

92

39

100

40 -187

-4

15

+4

22

11

30

16

37

20

45

24

52

27

60

30

68

33

76

35

84

38

92

40

100

41 42 43 44 45

41 -363

-12

10

-1

17

+7

24

13

32

18

39

22

46

25

53

29

61

31

68

34

76

3/

34

"39"

92

41

100

42 -235

-7

12

+3

19

10

26

15

33

20

40

23

47

27

54

30

62

33

69

35

77

38

84

40

92

42

100

43 -491

-158-2

14

+6

21

12

28

17

35

21

41

25

48

28

55

31

62

34

70

36

77

39

85

41

92

43

100

44

-294-9

10

+2

17

9

23

14

29

19

36

23

43

26

49

29

56

32

63

35

70

37

78

40

85

42

92

44

100

45 -186

-4

12

+5

19

11

25

16 21

37

24 28

fl

31

57

34

6¿t

36

71

39

7?

41 43

?3

45 46 47 48 49 50

nOY RillR

46 -35?

-1180

14

+7

20

13

26

18

32

22

39

26

45

29

52

32

58

35

65

37

72

40

79

42

86

44

93

46

100

TEMPERATURES 47 -225

-6

10

+3

16

10

22

16

28

20

34

24

40

27

46

31

53

33

59

36

66

39

72

41

79

43

86

45

93

47

100

48 -451

-147

-2

12

+6

13

13

24

18

29

22

35

26

41

29

1 *7

32

54

35

60

37

66

40

73

42

79

44

36

46

93

48

100

49 -273

-89+2

14

9

20

15

25

20

31

24

37

27

42

30

48

33

54

36

61

39

67

41

73

43

80

4b

86

4/

93

49

100

50 -175

-3

10

+5

16

12

21

17

27

21

32

25

38

29

44

32

49

35

55

37

61

40

63

42 44 46

87„

48 50

100

51 52 53 54 55

51 -33?

-117

+1

1?

8

17

14

23

19

28

23

34

27

39

30

45

33

50

36

56

39

62

41

63

43

74

45

81

47

87

49

93

51

100

52 -214

-59+4

14

11

19

17

24

21

29

25

35

29

40

32

46

35

51

37

57

40

63

42

69

44

75

46

31

48

87

50

94

52

100

53 -421

-136

-1

11

+8

16

14

21

19

26

23

31

27

36

30

41

33

47

36

52

39

58

41

64

43

69

45

75

47

81

49

87

51

94

53

100

54 -2

53

-78+3

1?

11

17

16

22

21

27

25

32

28

37

32

42

35

48

37

53

40

59

42

64

44

70

47

76

49

82

50

38

52

94

54

100

55 -57 -155

-29+7

14

13

19

18 23

23

27

33

30

38

33 36

¿,9

39

?4

41

J9

43

65J

46

JO.

48 50 51

M.

53 55

100

56 57 53 59 60

56 -292

-87+3

11

10

16

16

20

21

25

25

30

28

35

32

39

35

44

37

50

40

55

42

60

45

65

47

71

49

77

51

82

53

38

54

94

56

100

57 -174

-38

+6

13

13

17

18

22

23

26

27

31

30

36

33

41

36

45

39

50

41

56

44

61

46

66

48

71

50

77

52

83

54

88

55

94

57

100

58 -332

-106

+2

10

10

14

16

19

21

23

25

28

28

32

32

37

35

42

38

46

40

51

43

56

45

61

47

67

49

72

51

77

53

83

55

38

56

94

58

100

59 -193

-47+6

12

13

16

18

20

23

24

27

29

30

33

33

38

36

43

39

47

41

52

44

57

46

62

48

67

50

72

52

78

54

83

56

89

57

94

59

100

60 -381

-115+19

9

13

15

17

20

21

25

26

29

30

32

34

35

39

38

44

40

48

43

53

45

53

47

63

49

68

51

73

53

78

55

83

57

89

58

94

60

100
WET BULB TEMPERATURES

40 41 42 43 1

44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

61 -211

-47+5

11

12

15

18

19

23

2Í

27

27

30

31

34

36

36

40

39

44

42

49

44

54

46

58

48

63

50

68

52

73

54

78

56

84

58

89

59

?4

61

100

62 -441

-124+189

12

15

16

20

20

25

24

29

28

32

32

35

37

38

41

41

45

43

50

45

54

48

59

50

64

52

69

54

74

55

79

57

84

59

89

60

95

62

100

63 -23?

-56+5

10

12

14

18

17

23

21

.27

25

31

29

34

33

37

38

39

42

42

46

44

51

47

55

49

60

51

64

53

69

55

74

56

79

58

84

60

89

61

95

63

100

64 -501

-134

0R

+9

11

15

15

21

19

25

23

29

26

32

30

35

34

38

39

41

43

43

47

46

51

48

56

50

60

52

65

54

70

56

74

57

79

59

84

61

89 . 6295

64

100

65 -252

-56+5912

13

IB

16

23

20 , 27

24

31

28

34

31

37

3?

40P42 45 47

52

49

><>

51

61

53

65

55

70

57

75

59 60

85

62

?0

63

95

65

109

66 67 68 69 70

66 -57 -134

07+9

10

15

14

21

IS

25

21

29

25

33

29

36

32

39

36

41

40

44

44

46

49

48

53

50

57

52

62

54

66

56

71

58

75

60

80

61

85

63

90

64

95

66

100

67 -267

-65

+5S

12

12

18

15

23

19

27

22

31

26

34

30

37

34

40

37

43

41

45

45

47

49

50

54

52

58

54

62

55

66

57

71

59

76

61

80

62

85

64

90

65

95

67

100

68 -141

07

+9

10

16

13

21

17

25

?0

29

74

33

?7

36

31

39

34

42

3S

44

4?

47

46

49

50

51

54

53

58

55

63

57

67

58

71

60

76

62

81

63

85

65

90

67

95

68

inn

69 -262

-65

+5813

11

19

14

23

1R

28

21

31

25

35

28

38

32

41

35

43

39

46

43

48

47

50

51

52

55

54

59

56

63

58

67

60

72

61

76

63

81

64

85

66

90

68

95

69

100

70 -14

0

f.

+9116

1?

21

1IÍ

26

1?

30

??

33 - 36 39

13

42

1(i

45 47

44

49

40

51 53 55

(in

57

fi4

59

fift

61

7?

62

77

64 66

«fi

67

90

69

91

70

100 71 72 73 74 75

71 -26?

-55+5a13

11

19

14

24

17

28

?0

32

73

35

77

38

30

41

34

44

37

46

41

48

45

51

4«

53

52

55

56

56

60

58

64

60

68

62

73

63

77

65

81

67

86

68

9(T

70

95

71

100

72 -133

+1610916

1?

22

15

26

IB

30

71

34

74

37

79

40

31

43

35

45

38

47

47

50

45

52

49

54

53

56

57

58

61

59

65

61

69

63

73

64

77

66

87

68

86

69

91

71

91

72

100

73 -26?

-54+6713

10

19

13

24

16

29

19

32

77

36

25

39

79

41

32

44

35

47

39

49

47

51

46

53

50

55

53

57

57

59

61

61

65

62

69

64

73

66

77

67

82

69

86

70

91

72

95

73

100

74 -133

+1610«17

11

22

14

27

17

31

20

34

23

37

26

40

30

43

33

46

36

48

40

50

43

52

47

54

50

56

54

58

58

60

62

62

66

63

70

65

74

67

78

68

82

70

86

71

91

73

95

74

100

75 -25 -44

+67

14

10

20

1'

25

11

29

11

33

21

36

24

39

27

42

11

45

14

47

17

49

40

52

44

54

47

56

jl

58

15

59

5S

61

fi?,

63

fifi

65

70

66

74

68

7ft

69

9i

71

f)7

72

91

74

95

75

10ft 76 77 78 79 80

(ES

76 -57 -123

+2511817

11

23

14

27

16

31

19

35

22

38

25

41

28

44

31

46

35

49

38

51

41

53

45

55

48

57

52

59

55

61

59

62

63

64

66

66

70

67

74

69

78

70

82

72

87

73

91

75

95

76

100

BULB

PERATUf

77 -232

-34

+77

15921

12

25

15

30

18

33

20

37

23

40

26

43

29

45

32

48

35

50

39

52

42

54

45

56

49

58

52

60

56

62

59

63

63

65

67

67

71

68

75

70

79

71

83

73

87

74

91

76

96

77

100

78 -49 -113

+35

12818

10

23

13

28

16

32

19

35

21

39

24

41

27

44

30

47

33

49

36

51

39

53

43

56

46

57

49

59

53

61

56

63

60

65

63

66

67

68

71

69

75

71

79

72

83

74

87

75

91

77

96

78

100

79 -212

-24+86

15921

12

26

14

30

17

34

20

37

22

40

25

43

28

46

31

48

34

51

37

53

40

55

43

57

47

59

50

61

53

62

57

64

60

66

64

67

68

69

71

70

75

72

79

73

83

75

87

76

91

78

96

79

100

80 -43 -93

+45

12819

10

24

13

29

15

33

18

36

21

39

2?

42

26

45

29

47

}2

50

?5

52

38

54

41

56

44

58

47

60

50

62

54

64

57

65

61

67

64

68

68

70

72

72

75 79

74

?3

76

?7

77

?1

79 80 81 82 83 84 85

81 -192

-14

+96

16922

11

27

14

31

16

35

19

38

21

41

24

44

27

46

30

49

33

51

35

53

38

55

42

57

45

59

48

61

51

63

54

65

58

66

61

68

65

70

68

71

72

73

76

74

80

76

83

77

87

78

92

80

96

81

100

DRY 82 -371

-73+55137

20

10

25

12

29

15

33

17

37

20

40

22

43

25

45

28

48

31

50

33

53

36

55

39

57

42

59

45

61

48

6-Í

52 55 58 62 65

71

69

72

72

74

76

75

80

77

84

78

88

79

92

81

96

82

100

TEM 83 -162

04+ 106179

23

11

28

13

32

16

35

18

39

21

42

23

44

26

47

29

50

31

52

34

54

37

56

40

58

43

60

46

62

49 52 55 59 62

70

65

72

69

73

73

75

76

76

80

78

84

79

33

80

92

82

96

83

100

84 -311

-63+65

14721

10

26

12

30

14

34

17

37

19

41

22

43

24

46

27

49

29

51

32

53

35

55

38

57

41

59

43

61

46

63

50

65

53

67

56

68

59

70

62

71

66

73

69

74

73

76

76

77

80

79

34

80

88

81

92

83

96

84

100

85 -14 +2

If

11 18 24u28

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33

15

36

18

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72

66

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81

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92

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199

86 87 88 39 90

86 -261

-43

+8515722927

12

31

14

35

16

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21

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23

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26

49

28

52

31

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56

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67

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70

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73

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38

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92

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100

87 -112

+34

12619825

10

29

13

33

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37

17

40

19

43

22

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24

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27

51

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32

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70

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80

81

82

84

83

88

84

92

86

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100

83 -221

-23+95177239

28U32

13

36

16

39

18

42

20

45

22

48

25

50

27

53

30

55

32

57

35

59

38

61

40

63

43

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46

66

49

68

52

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55

71

58

73

61

74

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76

67

77

71

79

74

80

77

81

81

83

85

84

88

85

92

87

96

88

100

89 -45 -82

+54146208

26

10

30

12

34

14

38

17

41

19

44

21

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23

49

26

52

28

54

30

56

33

58

36

60

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62

41

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66

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52

71

55

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58

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61

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64

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68

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71

80

74

81

78

82

31

84

35

85

88

86

92

88

96

89

100

90 -171

03+ 11518724 29 33

13

37

15

40

17

43

20

46

22

48

24

51

26

53

29

55

31

58

.34

60

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44

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69

50

70

53

72

55

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65

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63

79

71

81

74

82

73

84

_8i

85

85

86

89

87

.JL

89 90

100
WET BULB TEMPERATURES

54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95

91

-341

-52+7415622827

10

31

12

35

14

39

16

42

18

45

20

48

23

50

25

53

27

55

29

57

32

59

34

61

37

63

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58

47

70

50

71

53

73

56

75

59

75

62

78

65

79

68

80

71

82

75

83

78

85

82

86

85

87

89

88

92

90

96

91

100

92 -132

+33125197259

30U

34

13

37

15

41

17

44

19

47

21

49

23

52

26

54

28

56

30

58

33

60

35

52

37

64

40

66

43

68

45

69

48

71

51

73

53

74

56

76

59

77

62

79

65

80

68

82

72

83

75

84

78

86

82

87

85

88

89

89

92

91

96

92

100

93

-251

-33

+94

176238

28

10

32

12

36

14

40

16

43

18

46

20

48

22

51

24

53

26

56

28

58

31

60

33

52

36

54

38

65

41

67

43

69

46

71

48

72

51

74

54

75

57

77

60

78

63

80

66

81

69

83

72

84

75

85

78

87

82

88

85

89

89

91

93

92

96

93

100

94 -102

+53145217

269

31

11

35

13

38

14

42

16

45

18

48

21

50

23

53

25

55

27

57

29

59

31

51

34

63

36

65

39

67

41

58

44

70

46

72

49

73

52

75

54

76

57

78

60

79

63

81

66

82

69

84

72

85

75

86

79

88

82

89

85

90

89

92

93

93

96

94

100

95 -201

03

4-114

186

24829

10

33

11

37

13

41

15

44

17

47

19

49

21

52

23

54

25

56

28

59

30

51

32

63

34

54

37

66

39

68

42

70

44

71

47

73

49

75

52

76

55

78

57

79

60

81

63

82

66

83

69

85

72

86

76

87

79

89

82

90

86

91

89

93

93

94

96

95

100

96 -39 -62

+74155

227

279

32

10

36

12

39

14

43

16

46

18

48

20

51

22

53

24

56

26

58

28

50

30

62

33

64

35

66

37

68

40

69

42

71

45

73

47

74

50

76

52

77

55

79

58

80

61

82

64

83

67

84

70

86

73

87

76

88

79

90

82

91

86

92

89

94

93

95

96

97 -141

+23

12420625830

10

35

11

38

13

42

15

45

17

48

19

50

21

53

23

55

25

57

27

59

29

61

31

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33

55

36

67

38

69

40

71

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72

45

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48

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50

77

53

78

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80

58

81

61

83

64

84

67

85

70

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73

88

76

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79

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83

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93

98 -281

-32+94

175

237299

33

10

37

12

40

14

44

16

47

18

49

19

52

21

54

23

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25

59

27

61

30

53

32

65

34

67

36

58

38

70

41

72

43

73

46

75

48

77

51

78

53

80

56

81

59

82

61

84

64

85

57

87

70

88

73

89

76

91

79

92

83

93

85

94

89

99 -101

+5314521627832936

11

39

13

43

15

46

16

48

18

51

20

54

22

56

24

58

26

60

28

52

30

64

32

66

34

58

37

70

39

71

41

73

44

75

46

76

48

78

51

79

54

81

56

82

59

84

62

85

65

86

67

88

70

89

73

90

76

92

80

93

83

94

86

100 -201

02fll4195

257

309

34

10

48

12

42

14

45

15

48

17

50

19

53

21

55

23

57

25

60

27

62

29

54

31

66

33

67

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73

42

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54

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62

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65

87

68

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71

90

74

n

77

93

80

94

83

101 -40 -62

+83165236288339

37

11

40

13

44

14

47

16

49

18

52

20

54

21

57

23

59

25

61

27

63

29

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31

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33

69

36

70

38

72

40

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42

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49

80

52

81

54

83

57

84

60

85

62

87

65

88

68

90

71

91

74

92

77

94

80

102 -141

+33134215267

319

36

10

39

12

43

13

46

15

49

17

51

18

54

20

56

22

58

24

61

26

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28

65

30

66

32

68

34

70

36

72

38

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77

45

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50

81

52

83

55

84

57

85

60

87

63

88

65

90

58

91

71

92

74

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77

103 -261

-22HO3185

246

30834938U42

12

45

14

48

16

50

17

53

19

55

21

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23

60

25

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50

82

53

84

55

85

58

87

60

88

63

89

65

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68

92

71

93

74

104 -81

+53

154226287339

37

10

40

12

44

13

47

15

50

16

52

18

55

20

57

22

59

23

61

25

63

27

55

29

67

31

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33

71

35

73

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39

76

41

77

44

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46

80

48

82

51

83

53

85

55

86

58

88

61

89

63

90

55

92

69

93

72

105 -IB1

+22124

205

266

31835939H

43

12

46

14

49

15

51

17

55

19

56

20

59

22

51

24

63

26

65

28

67

30

69

31

70

33

72

35

74

38

75

40

77

42

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44

80

46

82

49

83

51

85

53

85

55

87

58

89

61

90

63

91

66

93

69

106 -34 -42

+93

184

24629734838

10

42

11

45

13

48

14

51

16

53

18

56

19

58

21

60

23

62

25

64

26

55

28

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30

70

32

72

34

73

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40

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42

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44

81

47

83

49

84

51

85

54

87

55

88

59

90

61

91

64

92

66

107 -111

+52154

225286

338379

41

11

44

12

47

14

50

15

53

17

55

18

57

20

60

22

62

23

54

25

66

27

68

29

70

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32

73

34

75

36

76

38

78

41

79

43

81

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83

47

84

49

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52

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54

88

56

90

59

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51

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54

108 -221

02+ 123204266317 "s

39

10

43

11

46

13

49

14

52

16

54

17

57

19

59

21

61

22

63

24

55

26

67

27

69

29

71

31

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35

76

37

78

39

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41

81

43

82

45

84

47

85

50

87

52

88

54

89

57

91

59

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62

109 -46 -61

+83174245296

34838942

11

45

12

48

13

51

15

54

16

56

18

58

20

61

21

63

23

65

24

67

26

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39

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41

82

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110 -141

+42143

225

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10

44

11

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13

50

14

53

15

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58

19

60

20

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22

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23

55

25

68

27

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80

40

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48

87

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53

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ES

111 -26 -12

+ 113194265316368

39943

10

46

12

49

13

52

15

55

16

57

18

59

19

62

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22

66

24

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26

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40

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112 -71

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17324529634738842

10

45

11

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12

51

14

54

15

56

17

59

18

51

20

63

21

65

23

67

24

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113 -161

+32

143224285

33737841944

10

48

12

50

13

53

14

56

16

58

17

60

19

63

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55

22

67

23

69

25

70

27

72

28

74

30

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32

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33

79

35

81

37

82

39

84

41

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43

87

45

88

47

89

49-

91

51

114 -31 -21

+113194265

316

367408

43

10

47

11

50

12

52

14

55

15

57

16

60

18

52

19

64

21

66

22

68

24

70

25

72

27

74

29

75

30

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32

79

34

80

36

82

38

83

39

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41

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43

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45

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50

115 -91

+72173244

295

347

39842946

10

49

12

52

13

54

14

57

16

59

17

61

18

64

20

66

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23

70

24

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29

77

31

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33

80

34

81

36

83

38

85

40

86

42

87

44

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46

90

48

DRY BULB

116 -181

+32143

224285

33637741845

10

48U51

12

54

13

55

15

59

16

61

17

63

19

65

20

67

22

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25

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26

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28

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30

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31

80

33

81

35

83

37

84

38

86

40

87

42

89

44

90

46

TEMPERATUR

117 -35 -31

+ 112193264

316

367408

44947

10

50

11

53

13

55

14

58

15

60

17

63

18

65

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21

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22

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24

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27

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79

32

81

33

82

35

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37

85

39

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41

88

43

90

44

118 -91

+72173244

305

35639743846

10

49

11

52

12

55

13

57

15

60

16

62

17

64

19

66

20

68

21

70

23

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26

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77

29

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31

80

32

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34

84

36

85

37

87

39

88

41

89

43

119 -191

+2114222428533638742845948

10

51

11

54

13

57

14

59

15

61

16

64

18

56

19

68

20

70

22

72

23

73

25

75

26

77

28

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29

80

31

82

33

83

34

85

36

86

38

88

40

89

41