12-1

Introduction

In aviation, weather service is a combined effort of the 

National Weather Service (NWS), Federal Aviation 

Administration (FAA), Department of Defense (DOD), other 

aviation groups, and individuals. Because of the increasing 

need for worldwide weather services, foreign weather 

organizations also provide vital input.

While weather forecasts are not 100 percent accurate, 

meteorologists, through careful scientific study and computer 

modeling, have the ability to predict weather patterns, trends, 

and characteristics with increasing accuracy. Through a 

complex system of weather services, government agencies, 

and independent weather observers, pilots and other aviation 

professionals receive the benefit of this vast knowledge base 

in the form of up-to-date weather reports and forecasts. 

These reports and forecasts enable pilots to make informed 

decisions regarding weather and flight safety before and 

during a flight.

Aviation Weather Services

Chapter 12
12-2

Observations

The data gathered from surface and upper altitude 

observations form the basis of all weather forecasts, 

advisories, and briefings. There are four types of weather 

observations: surface, upper air, radar, and satellite.

Surface Aviation Weather Observations

Surface aviation weather observations (METARs) are a 

compilation of elements of the current weather at individual 

ground stations across the United States. The network is 

made up of government and privately contracted facilities 

that provide continuous up-to-date weather information. 

Automated weather sources, such as the Automated Weather 

Observing Systems (AWOS), Automated Surface Observing 

Systems (ASOS), Air Route Traffic Control Center (ARTCC) 

facilities, as well as other automated facilities, also play a 

major role in the gathering of surface observations.

Surface observations provide local weather conditions and 

other relevant information for a radius of five miles of a 

specific airport. This information includes the type of report, 

station identifier, date and time, modifier (as required), wind, 

visibility, runway visual range (RVR), weather phenomena, 

sky condition, temperature/dew point, altimeter reading, and 

applicable remarks. The information gathered for the surface 

observation may be from a person, an automated station, or 

an automated station that is updated or enhanced by a weather 

observer. In any form, the surface observation provides 

valuable information about individual airports around the 

country. Although the reports cover only a small radius, the 

pilot can generate a good picture of the weather over a wide 

area when many reporting stations are looked at together.

Air Route Traffic Control Center (ARTCC)

The ARTCC facilities are responsible for maintaining 

separation between flights conducted under instrument flight 

rules (IFR) in the en route structure. Center radars (Air Route 

Surveillance Radar (ARSR)) acquire and track transponder 

returns using the same basic technology as terminal radars. 

Earlier center radars displayed weather as an area of slashes 

(light precipitation) and Hs (moderate rainfall). Because the 

controller could not detect higher levels of precipitation, pilots 

had to be wary of areas showing moderate rainfall. Newer radar 

displays show weather as three shades of blue. Controllers can 

select the level of weather to be displayed. Weather displays 

of higher levels of intensity make it difficult for controllers to 

see aircraft data blocks, so pilots should not expect air traffic 

control (ATC) to keep weather displayed continuously.

Upper Air Observations

Observations of upper air weather are more challenging 

than surface observations. There are only two methods 

by which upper air weather phenomena can be observed: 

radiosonde observations and pilot weather reports (PIREPs). 

A radiosonde is a small cubic instrumentation package 

which is suspended below a six foot hydrogen or helium 

filled balloon. Once released, the balloon rises at a rate of 

approximately 1,000 feet per minute (fpm). As it ascends, 

the instrumentation gathers various pieces of data such as 

air temperature and pressure, as well as wind speed and 

direction. Once the information is gathered, it is relayed to 

ground stations via a 300 milliwatt radio transmitter. 

The balloon flight can last as long as 2 hours or more and 

can ascend to altitudes as high as 115,000 feet and drift as 

far as 125 miles. The temperatures and pressures experienced 

during the flight can be as low as -130 °F and pressures as low 

as a few thousandths of what is experienced at sea level.

Since the pressure decreases as the balloon rises in the 

atmosphere, the balloon expands until it reaches the limits 

of its elasticity. This point is reached when the diameter has 

increased to over 20 feet. At this point, the balloon pops and 

the radiosonde falls back to Earth. The descent is slowed by 

means of a parachute. The parachute aids in protecting people 

and objects on the ground. Each year over 75,000 balloons 

are launched. Of that number, 20 percent are recovered and 

returned for reconditioning. Return instructions are printed 

on the side of each radiosonde.

Pilots also provide vital information regarding upper air 

weather observations and remain the only real-time source 

of information regarding turbulence, icing, and cloud heights. 

This information is gathered and filed by pilots in flight. 

Together, PIREPs and radiosonde observations provide 

information on upper air conditions important for flight 

planning. Many domestic and international airlines have 

equipped their aircraft with instrumentation that automatically 

transmits inflight weather observations through the DataLink 

system to the airline dispatcher who disseminates the data to 

appropriate weather forecasting authorities.

Radar Observations

Weather observers use four types of radar to provide 

information about precipitation, wind, and weather systems. 

1. The WSR-88D NEXRAD radar, commonly called 

Doppler radar, provides in-depth observations that 

inform surrounding communities of impending 

weather. Doppler radar has two operational modes: 

clear air and precipitation. In clear air mode, the radar 

is in its most sensitive operational mode because a 

slow antenna rotation allows the radar to sample the 

atmosphere longer. Images are updated about every 

10 minutes in this mode. 
12-3

Figure 12-1. Example of a weather radar scope.

Figure 12-2. WSR-88D Weather Radar Echo Intensity Legend.

Weather Radar Echo Intensity 

Light

Moderate

Heavy

Extreme

Reflectivity (dBZ) Ranges

<30 dBZ

30–40 dBZ

>40–50

50+ dBZ

Figure 12-3. WSR-88D Weather Radar Precipitation Intensity 

Terminology.

 Precipitation targets provide stronger return signals 

therefore the radar is operated in the Precipitation 

mode when precipitation is present. A faster antenna 

rotation in this mode allows images to update at 

a faster rate, approximately every 4 to 6 minutes. 

Intensity values in both modes are measured in dBZ 

(decibels of Z) and depicted in color on the radar 

image. [Figure 12-1] Intensities are correlated to 

intensity terminology (phraseology) for air traffic 

control purposes. [Figure 12-2 and 12-3]

2. FAA terminal doppler weather radar (TDWR), installed 

at some major airports around the country, also aids in 

providing severe weather alerts and warnings to ATC. 

Terminal radar ensures pilots are aware of wind shear, 

gust fronts, and heavy precipitation, all of which are 

dangerous to arriving and departing aircraft. 

3. The third type of radar commonly used in the detection 

of precipitation is the FAA airport surveillance radar. 

This radar is used primarily to detect aircraft, but it 

also detects the location and intensity of precipitation 

which is used to route aircraft traffic around severe 

weather in an airport environment.

4. Airborne radar is equipment carried by aircraft to 

locate weather disturbances. The airborne radars 

generally operate in the C or X bands (around 6 

GHz or around 10 GHz, respectively) permitting 

both penetration of heavy precipitation, required for 

determining the extent of thunderstorms, and sufficient 

reflection from less intense precipitation. 

Satellite

Advancement in satellite technologies has recently allowed for 

commercial use to include weather uplinks. Through the use 

of satellite subscription services, individuals are now able to 

receive satellite transmitted signals that provide near real-time 

weather information for the North American continent.

Satellite Weather

Recently private enterprise and satellite technology have 

expanded the realm of weather services. Pilots now have 

the capability of receiving continuously updated weather 

across the entire country at any altitude. No longer are pilots 

restricted by radio range or geographic isolations such as 

mountains or valleys.

In addition, pilots no longer have to request specific 

information from weather briefing personnel directly. When 

the weather becomes questionable, radio congestion often 

increases, delaying the timely exchange of valuable inflight 

weather updates for a pilot’s specific route of flight. Flight 

Service Station (FSS) personnel can communicate with only 

one pilot at a time, which leaves other pilots waiting and 

flying in uncertain weather conditions. Satellite weather 

provides the pilot with a powerful resource for enhanced 

situational awareness at any time. Due to continuous satellite 

broadcasts, pilots can obtain a weather briefing by looking at 

a display screen. Pilots have a choice between FAA-certified 

devices or portable receivers as a source of weather data.
12-4

Figure 12-5. Satellite AIRMET.

Figure 12-4. Satellite SIGMET.

Satellite Weather Products

Significant Meteorological Information (SIGMET) 

SIGMETs are weather advisories issued concerning weather 

significant to the safety of all aircraft. SIGMET advisories 

can cover an area of at least 3,000 square miles and provide 

data regarding severe and extreme turbulence, severe icing, 

and widespread dust or sandstorms that reduce visibility to 

less than three miles. [Figure 12-4]

Airmen’s Meteorological Information (AIRMET)

AIRMETs are weather advisories issued only to amend 

the area forecast concerning weather phenomena which 

are of operational interest to all aircraft and potentially 

hazardous to aircraft having limited capability because of 

lack of equipment, instrumentation, or pilot qualifications. 

AIRMETs concern weather of less severity than that covered 

by SIGMETs or convective SIGMETs. AIRMETs cover 

moderate icing, moderate turbulence, sustained winds of 30 

knots or more at the surface, widespread areas of ceilings 

less than 1,000 feet and/or visibility less than three miles, 

and extensive mountain obscurement. [Figure 12-5]

Service Outlets

Service outlets are government or private facilities that 

provide aviation weather services. Several different 

government agencies, including the FAA, National Oceanic 

and Atmospheric Administration (NOAA), and the NWS 

work in conjunction with private aviation companies to 

provide different means of accessing weather information.

Automated Flight Service Station (AFSS)

The AFSS is the primary source for preflight weather 

information. A preflight weather briefing from an AFSS can 

be obtained 24 hours a day by calling 1-800-WX BRIEF from 

almost anywhere in the United States. In areas not served by 

an AFSS, NWS facilities may provide pilot weather briefings. 

Telephone numbers for NWS facilities and additional 

numbers for AFSS can be found in the Airport/Facility 

Directory (A/FD) or in the United States Government section 

of the telephone book.

The AFSS also provides inflight weather briefing services, as 

well as scheduled and unscheduled weather broadcasts. An 

AFSS may also furnish weather advisories to flights within 

the AFSS region of authority.

Transcribed Information Briefing Service (TIBS)

The Transcribed Information Briefing Service (TIBS) is 

a service prepared and disseminated by selected AFSS. It 

provides continuous telephone recordings of meteorological 

and aeronautical information. Specifically, TIBS provides 

area and route briefings, airspace procedures, and special 

announcements. It is designed to be a preliminary briefing 

tool and is not intended to replace a standard briefing from 

a FSS specialist. The TIBS service is available 24 hours a 

day and is updated when conditions change, but it can only 

be accessed by a touchtone phone. The phone numbers for 

the TIBS service are listed in the A/FD.

Direct User Access Terminal Service (DUATS)

The Direct User Access Terminal Service (DUATS), which is 

funded by the FAA, allows any pilot with a current medical 

certificate to access weather information and file a flight 

plan via computer. Two methods of access are available to 

connect with DUATS. The first is via the Internet at http://

www.duats.com. The second method requires a modem and a 

communications program supplied by a DUATS provider. To 

access the weather information and file a flight plan by this 

method, pilots use a toll free telephone number to connect the 

user’s computer directly to the DUATS computer. The current 

vendors of DUATS service and the associated phone numbers 

are listed in Chapter 7, Safety of Flight, of the Aeronautical 

Information Manual (AIM).
12-5

Symbol indicates HIWAS

Figure 12-6. HIWAS availability is shown on sectional chart.

En Route Flight Advisory Service (EFAS)

A service specifically designed to provide timely en route 

weather information upon pilot request is known as the en 

route flight advisory service (EFAS), or Flight Watch. EFAS 

provides a pilot with weather advisories tailored to the type 

of flight, route, and cruising altitude. EFAS can be one of 

the best sources for current weather information along the 

route of flight.

A pilot can usually contact an EFAS specialist from 6 a.m. to 10 

p.m. anywhere in the conterminous United States and Puerto 

Rico. The common EFAS frequency, 122.0 MHz, is established 

for pilots of aircraft flying between 5,000 feet above ground 

level (AGL) and 17,500 feet mean sea level (MSL).

Hazardous Inflight Weather Advisory (HIWAS)

Hazardous Inflight Weather Advisory (HIWAS) is a national 

program for broadcasting hazardous weather information 

continuously over selected navigation aids (NAVAIDs). The 

broadcasts include advisories such as AIRMETS, SIGMETS, 

convective SIGMETS, and urgent PIREPs. These broadcasts 

are only a summary of the information, and pilots should 

contact a FSS or EFAS for detailed information. NAVAIDs 

that have HIWAS capability are depicted on sectional charts 

with an “H” in the upper right corner of the identification 

box. [Figure 12-6]

Transcribed Weather Broadcast (TWEB) (Alaska 

Only) 

Equipment is provided in Alaska by which meteorological 

and aeronautical data are recorded on tapes and broadcast 

continuously over selected low or medium frequency (L/MF) 

and very high frequency (VHF) omnidirectional radio range 

navigation system (VOR) facilities. Broadcasts are made 

from a series of individual tape recordings, and changes, as 

they occur, are transcribed onto the tapes. The information 

provided varies depending on the type equipment available. 

Generally, the broadcast contains a summary of adverse 

conditions, surface weather observations, PIREPS, and a 

density altitude statement (if applicable). At the discretion of 

the broadcast facility, recordings may also include a synopsis, 

winds aloft forecast, en route and terminal forecast data, and 

radar reports. At selected locations, telephone access to the 

TWEB has been provided (TEL-TWEB). Telephone numbers 

for this service are found in the Supplement Alaska A/FD. 

These broadcasts are made available primarily for preflight 

and inflight planning, and as such, should not be considered 

as a substitute for specialist-provided preflight briefings. 

Weather Briefings

Prior to every flight, pilots should gather all information vital 

to the nature of the flight. This includes an appropriate weather 

briefing obtained from a specialist at a FSS, AFSS, or NWS.

For weather specialists to provide an appropriate weather 

briefing, they need to know which of the three types of 

briefings is needed—standard, abbreviated, or outlook. Other 

helpful information is whether the flight is visual flight rules 

(VFR) or IFR, aircraft identification and type, departure 

point, estimated time of departure (ETD), flight altitude, route 

of flight, destination, and estimated time en route (ETE).

This information is recorded in the flight plan system and a 

note is made regarding the type of weather briefing provided. 

If necessary, it can be referenced later to file or amend a 

flight plan. It is also used when an aircraft is overdue or is 

reported missing.

Standard Briefing

A standard briefing is the most complete report and provides 

the overall weather picture. This type of briefing should be 

obtained prior to the departure of any flight and should be 

used during flight planning. A standard briefing provides the 

following information in sequential order if it is applicable 

to the route of flight.

1. Adverse conditions—this includes information about 

adverse conditions that may influence a decision to 

cancel or alter the route of flight. Adverse conditions 

include significant weather, such as thunderstorms or 

aircraft icing, or other important items such as airport 

closings.

2. VFR flight not recommended—if the weather for 

the route of flight is below VFR minimums, or if 

it is doubtful the flight could be made under VFR 

conditions due to the forecast weather, the briefer may 

state that VFR is not recommended. It is the pilot’s 

decision whether or not to continue the flight under 

VFR, but this advisory should be weighed carefully.
12-6

3. Synopsis—an overview of the larger weather picture. 

Fronts and major weather systems that affect the 

general area are provided.

4. Current conditions—this portion of the briefing contains 

the current ceilings, visibility, winds, and temperatures. 

If the departure time is more than 2 hours away, current 

conditions are not included in the briefing.

5. En route forecast—a summary of the weather forecast 

for the proposed route of flight.

6. Destination forecast—a summary of the expected 

weather for the destination airport at the estimated 

time of arrival (ETA).

7. Winds and temperatures aloft—a report of the winds 

at specific altitudes for the route of flight. The 

temperature information is provided only on request.

8. Notices to Airmen (NOTAM)—information pertinent 

to the route of flight which has not been published 

in the NOTAM publication. Published NOTAM 

information is provided during the briefing only when 

requested.

9. ATC delays—an advisory of any known ATC delays 

that may affect the flight.

10. Other information—at the end of the standard briefing, 

the FSS specialist provides the radio frequencies 

needed to open a flight plan and to contact EFAS. Any 

additional information requested is also provided at 

this time.

Abbreviated Briefing

An abbreviated briefing is a shortened version of the standard 

briefing. It should be requested when a departure has been 

delayed or when weather information is needed to update the 

previous briefing. When this is the case, the weather specialist 

needs to know the time and source of the previous briefing 

so the necessary weather information will not be omitted 

inadvertently. It is always a good idea to update weather 

whenever a pilot has additional time.

Outlook Briefing

An outlook briefing should be requested when a planned 

departure is 6 hours or more away. It provides initial forecast 

information that is limited in scope due to the timeframe of 

the planned flight. This type of briefing is a good source 

of flight planning information that can influence decisions 

regarding route of flight, altitude, and ultimately the go/no-go 

decision. A prudent pilot requests a follow-up briefing prior 

to departure since an outlook briefing generally only contains 

information based on weather trends and existing weather in 

geographical areas at or near the departure airport. A standard 

briefing near the time of departure ensures that the pilot has 

the latest information available prior to their flight.

Aviation Weather Reports

Aviation weather reports are designed to give accurate 

depictions of current weather conditions. Each report 

provides current information that is updated at different 

times. Some typical reports are METAR, PIREPs, and radar 

weather reports (SDs).

Aviation Routine Weather Report (METAR)

A METAR is an observation of current surface weather 

reported in a standard international format. While the 

METAR code has been adopted worldwide, each country is 

allowed to make modifications to the code. Normally, these 

differences are minor but necessary to accommodate local 

procedures or particular units of measure. This discussion of 

METAR will cover elements used in the United States.

Metars are issued hourly unless significant weather changes 

have occurred. A special METAR (SPECI) can be issued at 

any interval between routine METAR reports.

Example:

METAR KGGG 161753Z AUTO 14021G26 3/4SM

+TSRA BR BKN008 OVC012CB 18/17 A2970 RMK

PRESFR

A typical METAR report contains the following information 

in sequential order:

1. Type of report—there are two types of METAR 

reports. The first is the routine METAR report that 

is transmitted every hour. The second is the aviation 

selected SPECI. This is a special report that can be 

given at any time to update the METAR for rapidly 

changing weather conditions, aircraft mishaps, or 

other critical information.

2. Station identifier—a four-letter code as established 

by the International Civil Aviation Organization 

(ICAO). In the 48 contiguous states, a unique threeletter identifier is preceded by the letter “K.” For 

example, Gregg County Airport in Longview, Texas, is 

identified by the letters “KGGG,” K being the country 

designation and GGG being the airport identifier. 

In other regions of the world, including Alaska and 

Hawaii, the first two letters of the four-letter ICAO 

identifier indicate the region, country, or state. Alaska 

identifiers always begin with the letters “PA” and 

Hawaii identifiers always begin with the letters “PH.” 

A list of station identifiers can be found at an FSS or 

NWS office.
12-7

27A WSA 20K+ RWY 250 20

27D WSA 20K+ RWY 250 20

2MD 1MD 9 RWY 27 1MF 2MF 3MF

Figure 12-7. Example of what the controller sees on the ribbon 

display in the tower cab.

3. Date and time of report—depicted in a six-digit group 

(161753Z). The first two digits are the date. The last 

four digits are the time of the METAR, which is always 

given in coordinated universal time (UTC). A “Z” is 

appended to the end of the time to denote the time is 

given in Zulu time (UTC) as opposed to local time.

4. Modifier—denotes that the METAR came from an 

automated source or that the report was corrected. 

If the notation “AUTO” is listed in the METAR, the 

report came from an automated source. It also lists 

“AO1” or “AO2” in the remarks section to indicate 

the type of precipitation sensors employed at the 

automated station. 

 When the modifier “COR” is used, it identifies a 

corrected report sent out to replace an earlier report 

that contained an error (for example: METAR KGGG 

161753Z COR).

5. Wind—reported with five digits (14021) unless the 

speed is greater than 99 knots, in which case the 

wind is reported with six digits. The first three digits 

indicate the direction the true wind is blowing in 

tens of degrees. If the wind is variable, it is reported 

as “VRB.” The last two digits indicate the speed of 

the wind in knots unless the wind is greater than 99 

knots, in which case it is indicated by three digits. 

If the winds are gusting, the letter “G” follows the 

wind speed (G26). After the letter “G,” the peak gust 

recorded is provided. If the wind varies more than 60° 

and the wind speed is greater than six knots, a separate 

group of numbers, separated by a “V,” will indicate the 

extremes of the wind directions. Figure 12-7 shows 

how the TDWR/Weather System Processor (WSP) 

determines the true wind, as well as gust front/wind 

shear location.

6. Visibility—the prevailing visibility (3⁄4 SM) is reported 

in statute miles as denoted by the letters “SM.” It is 

reported in both miles and fractions of miles. At times, 

runway visual range (RVR) is reported following the 

prevailing visibility. RVR is the distance a pilot can 

see down the runway in a moving aircraft. When RVR 

is reported, it is shown with an R, then the runway 

number followed by a slant, then the visual range 

in feet. For example, when the RVR is reported as 

R17L/1400FT, it translates to a visual range of 1,400 

feet on runway 17 left.

7. Weather—can be broken down into two different 

categories: qualifiers and weather phenomenon 

(+TSRA BR). First, the qualifiers of intensity, 

proximity, and the descriptor of the weather will 

be given. The intensity may be light (-), moderate 

( ), or heavy (+). Proximity only depicts weather 

phenomena that are in the airport vicinity. The notation 

“VC” indicates a specific weather phenomenon is 

in the vicinity of five to ten miles from the airport. 

Descriptors are used to describe certain types of 

precipitation and obscurations. Weather phenomena 

may be reported as being precipitation, obscurations, 

and other phenomena such as squalls or funnel clouds. 

Descriptions of weather phenomena as they begin or 

end, and hailstone size are also listed in the remarks 

sections of the report. [Figure 12-8]

8. Sky condition—always reported in the sequence 

of amount, height, and type or indefinite ceiling/

height (vertical visibility) (BKN008 OVC012CB). 

The heights of the cloud bases are reported with a 

three-digit number in hundreds of feet AGL. Clouds 

above 12,000 feet are not detected or reported by an 

automated station. The types of clouds, specifically 

towering cumulus (TCU) or cumulonimbus (CB) 

clouds, are reported with their height. Contractions 

are used to describe the amount of cloud coverage and 

obscuring phenomena. The amount of sky coverage is 

reported in eighths of the sky from horizon to horizon. 

[Figure 12-9]

9. Temperature and dew point—the air temperature and 

dew point are always given in degrees Celsius (C) or 

(°C 18/17). Temperatures below 0 °C are preceded by 

the letter “M” to indicate minus.

10. Altimeter setting—reported as inches of mercury 

("Hg) in a four-digit number group (A2970). It is 

always preceded by the letter “A.” Rising or falling 

pressure may also be denoted in the remarks sections 

as “PRESRR” or “PRESFR” respectively.

11. Zulu time—a term used in aviation for UTC which 

places the entire world on one time standard.
12-8

Intensity or Proximity 1 Descriptor 2 Precipitation 3 Obscuration 4 Other 5

– Light

 Moderate (no qualifier)

+ Heavy

VC in the vicinity

MI Shallow

BC Patches

DR Low drifting

BL Blowing

SH Showers

TS Thunderstorms

FZ Freezing

PR Partial

DZ Drizzle

RA Rain

SN Snow

SG Snow grains

IC Ice crystals (diamond dust)

PL Ice pellets

GR Hail

GS Small hail or snow pellets

UP *Unknown precipitation

BR Mist

FG Fog

FU Smoke

DU Dust

SA Sand

HZ Haze

PY Spray

VA Volcanic ash

PO Dust/sand whirls

SQ Squalls

FC Funnel cloud

+FC Tornado or waterspout

SS Sandstorm

DS Dust storm

The weather groups are constructed by considering columns 1–5 in this table in sequence:

intensity, followed by descriptor, followed by weather phenomena (e.g., heavy rain showers(s) is coded as +SHRA).

* Automated stations only

Qualifier Weather Phenomena

Figure 12-8. Descriptors and weather phenomena used in a typical METAR.

Contraction

SKC, CLR, FEW

FEW

SCT

BKN

OVC

Sky Cover

Less than 1⁄8 (Clear)

1⁄82⁄ (Few)

3⁄84⁄ (Scattered)

5⁄87⁄8 (Broken)

⁄ or (Overcast)

Figure 12-9. Reportable contractions for sky condition.

12. Remarks—the remarks section always begins with the 

letters “RMK.” Comments may or may not appear in 

this section of the METAR. The information contained 

in this section may include wind data, variable visibility, 

beginning and ending times of particular phenomenon, 

pressure information, and various other information 

deemed necessary. An example of a remark regarding 

weather phenomenon that does not fit in any other 

category would be: OCNL LTGICCG. This translates 

as occasional lightning in the clouds and from cloud 

to ground. Automated stations also use the remarks 

section to indicate the equipment needs maintenance. 

Example:

METAR KGGG 161753Z AUTO 14021G26 3/4SM

+TSRA BR BKN008 OVC012CB 18/17 A2970 RMK

PRESFR

Explanation:

Routine METAR for Gregg County Airport for the 16th 

day of the month at 1753Z automated source. Winds are 

140 at 21 knots gusting to 26. Visibility is 3⁄4 statute mile. 

Thunderstorms with heavy rain and mist. Ceiling is broken 

at 800 feet, overcast at 1,200 feet with cumulonimbus clouds. 

Temperature 18 °C and dew point 17 °C. Barometric pressure 

is 29.70 "Hg and falling rapidly. 

Pilot Weather Reports (PIREPs)

PIREPs provide valuable information regarding the conditions 

as they actually exist in the air, which cannot be gathered from 

any other source. Pilots can confirm the height of bases and 

tops of clouds, locations of wind shear and turbulence, and 

the location of inflight icing. If the ceiling is below 5,000 

feet, or visibility is at or below five miles, ATC facilities 

are required to solicit PIREPs from pilots in the area. When 

unexpected weather conditions are encountered, pilots are 

encouraged to make a report to a FSS or ATC. When a pilot 

weather report is filed, the ATC facility or FSS will add it 

to the distribution system to brief other pilots and provide 

inflight advisories.

PIREPs are easy to file and a standard reporting form outlines 

the manner in which they should be filed. Figure 12-10 shows 

the elements of a PIREP form. Item numbers 1 through 5 are 

required information when making a report, as well as at least 

one weather phenomenon encountered. A PIREP is normally 

transmitted as an individual report, but may be appended to 

a surface report. Pilot reports are easily decoded and most 

contractions used in the reports are self-explanatory.
12-9

Symbol Meaning

Symbol Intensity

Contraction Operational Status

R

RW

S

SW

T

Rain

Rain Shower

Snow

Snow Shower

Thunderstorm

-

(none)

+

++

x

xx

Light

Moderate

Heavy

Very Heavy

Intense

Extreme

PPINE

PPINA

PPIOM

AUTO

Radar is operating normally but there are no

echoes being detected.

Radar observation is not available.

Radar is inoperative or out of service.

Automated radar report from WSR-88D.

Figure 12-11. Radar weather report codes.

1

2

3

4

5

6

7

8

9

10

11

12

13

XXX

UA

/OV

/TM

/FL

/TP

/SK

/WX

/TA

/WV

/TB

/IC

/RM

3-letter station identifier

Routine PIREP, UUA-Urgent PIREP.

Location

Time

Altitude/Flight level

Type Aircraft

Sky cover/Cloud layers

Weather

Air temperature in Celsius (C)

Wind

Turbulence

Icing

Remarks

Nearest weather reporting location to the reported phenomenon

Use 3-letter NAVAID idents only.

a. Fix: /OV ABC, /OV ABC 090025.

b. Fix: /OV ABC 045020-DEF, /OV ABC-DEF-GHI

4 digits in UTC: /TM 0915.

3 digits for hundreds of feet. If not known, use UNKN: /FL095, /FL310, /FLUNKN.

4 digits maximum. If not known, use UNKN: /TP L329, /TP B727, /TP UNKN.

Describe as follows:

a. Height of cloud base in hundreds of feet. If unknown, use UNKN.

b. Cloud cover symbol.

c. Height of cloud tops in hundreds of feet.

Flight visibility reported first:

Use standard weather symbols; intensity is not reported:

/WX FV02 R H, /WX FV01 TRW.

If below zero, prefix with a hyphen: /TA 15, /TA -06.

Direction in degrees magnetic north and speed in six digits:

/WV 270045, WV 280110.

Use standard contractions for intensity and type (use CAT or CHOP when

appropriate). Include altitude only if different from /FL, /TB EXTREME, /TB 

LGT-MDT BLO 090.

Describe using standard intensity and type contractions. Include altitude only if

different than /FL: /IC LGT-MDT RIME, /IC SVR CLR 028-045.

Use free from to clarify the report and type hazardous elements first:

/RM LLWS -15KT SFC-030 DURC RNWY 22 JFK.

Encoding Pilot Weather Reports (PIREPS)

Figure 12-10. PIREP encoding and decoding.

RAREPs provide information on the type, intensity, and 

location of the echo top of the precipitation. [Figure 12-11]

These reports may also include direction and speed of 

the area of precipitation, as well as the height and base of 

the precipitation in hundreds of feet MSL. RAREPs are 

especially valuable for preflight planning to help avoid 

areas of severe weather. However, radar only detects objects 

Example:

UA/OV GGG 090025/TM 1450/FL 060/TP C182/SK

080 OVC/WX FV 04R/TA 05/WV 270030/TB LGT/RM 

HVY RAIN

Explanation:

Type: .................................Routine pilot report

Location: .......................... 25 NM out on the 090° radial, 

 Gregg County VOR

Time: ................................ 1450 Zulu

Altitude or Flight Level: 6,000 feet

Aircraft Type: ................... Cessna 182

Sky Cover: ........................ 8,000 overcast

Visibility/Weather: ........... 4 miles in rain

Temperature: .....................5 °Celsius

Wind: ................................ 270° at 30 knots

Turbulence: .......................Light

Icing: ................................ None reported

Remarks: .......................... Rain is heavy

Radar Weather Reports (RAREP)

Areas of precipitation and thunderstorms are observed by radar 

on a routine basis. Radar weather reports (RAREPs) or storm 

detections (SDs) are issued by radar stations at 35 minutes 

past the hour, with special reports issued as needed.
12-10

Explanation:

The radar report gives the following information: The report 

is automated from Oklahoma City and was made at 1935 

UTC. The echo pattern for this radar report indicates a line of 

echos covering 8⁄10 of the area. Thunderstorms and very heavy 

rain showers are indicated. The next set of numbers indicates 

the azimuth that defines the echo (86° at 40 NM and 199° at 

115 NM). The dimension of this echo is given as 20 NM wide 

(10 NM on either side of the line defined by the azimuth and 

range). The cells within the line are moving from 240° at 25 

knots. The maximum top of the precipitation, as determined 

by radar and satellite, is 57,000 feet and it is located on the 

159° radial, 65 NM out. The last line indicates the intensity 

of the precipitation, for example in grid QM the intensity is 

3, or heavy precipitation. (1 is light and 6 is extreme.)

Aviation Forecasts

Observed weather condition reports are often used in the 

creation of forecasts for the same area. A variety of different 

forecast products are produced and designed to be used in 

the preflight planning stage. The printed forecasts that pilots 

need to be familiar with are the terminal aerodrome forecast 

(TAF), aviation area forecast (FA), inflight weather advisories 

(SIGMET, AIRMET), and the winds and temperatures aloft 

forecast (FD).

Terminal Aerodrome Forecasts (TAF)

A TAF is a report established for the five statute mile radius 

around an airport. TAF reports are usually given for larger 

airports. Each TAF is valid for a 30-hour time period, and is 

updated four times a day at 0000Z, 0600Z, 1200Z, and 1800Z. 

The TAF utilizes the same descriptors and abbreviations as 

used in the METAR report. The TAF includes the following 

information in sequential order:

1. Type of report—a TAF can be either a routine forecast 

(TAF) or an amended forecast (TAF AMD).

2. ICAO station identifier—the station identifier is the 

same as that used in a METAR.

3. Date and time of origin—time and date of TAF 

origination is given in the six-number code with the 

first two being the date, the last four being the time. 

Time is always given in UTC as denoted by the Z 

following the number group.

4. Valid period date and time—the valid forecast time 

period is given by a six-digit number group. The first 

two numbers indicate the date, followed by the twodigit beginning time for the valid period, and the last 

two digits are the ending time. 

in the atmosphere that are large enough to be considered 

precipitation. Cloud bases and tops, ceilings, and visibility 

are not detected by radar.

A typical RAREP will include:

• Location identifier and time of radar observation

• Echo pattern

1. Line (LN)—a line of precipitation echoes at least 

30 miles long, at least four times as long as it is 

wide, and at least 25 percent coverage within the 

line.

2. Area (AREA)—a group of echoes of similar type 

and not classified as a line.

3. Single cell (CELL)—a single isolated convective 

echo such as a rain shower.

• Area coverage in tenths

• Type and intensity of weather

• Azimuth, referenced to true north and range, in 

nautical miles from the radar site of points defining 

the echo pattern. For lines and areas, there will be two 

azimuth and range sets that define the pattern. For 

cells, there will be only one azimuth and range set.

• Dimension of echo pattern—given when the azimuth 

and range define only the center line of the pattern.

• Cell movement—movement is coded only for cells; 

it will not be coded for lines or areas.

• Maximum top of precipitation and location—

maximum tops may be coded with the symbols “MT” 

or “MTS.” If it is coded with “MTS,” it means that 

satellite data, as well as radar information was used 

to measure the top of the precipitation.

• If the contraction “AUTO” appears in the report, it 

means the report is automated from WSR-88D weather 

radar data.

• The last section is primarily used to prepare radar 

summary charts, but can be used during preflight 

to determine the maximum precipitation intensity 

within a specific grid box. The higher the number, the 

greater the intensity. Two or more numbers appearing 

after a grid box reference, such as PM34, indicates 

precipitation in consecutive grid boxes.

Example:

TLX 1935 LN 8 TRW++ 86/40 199/115

20W C2425 MTS 570 AT 159/65 AUTO

^MO1 NO2 ON3 PM34 QM3 RL2=
12-11

5. Forecast wind—the wind direction and speed forecast 

are given in a five-digit number group. The first three 

indicate the direction of the wind in reference to true 

north. The last two digits state the windspeed in knots 

as denoted by the letters “KT.” Like the METAR, 

winds greater than 99 knots are given in three digits.

6. Forecast visibility—given in statute miles and may 

be in whole numbers or fractions. If the forecast is 

greater than six miles, it will be coded as “P6SM.” 

7. Forecast significant weather—weather phenomena are 

coded in the TAF reports in the same format as the 

METAR. If no significant weather is expected during 

the forecast time period, the denotation “NSW” is 

included in the “becoming” or “temporary” weather 

groups.

8. Forecast sky condition—given in the same manner 

as the METAR. Only cumulonimbus (CB) clouds are 

forecast in this portion of the TAF report as opposed 

to CBs and towering cumulus in the METAR.

9. Forecast change group—for any significant weather 

change forecast to occur during the TAF time period, 

the expected conditions and time period are included 

in this group. This information may be shown as from 

(FM), becoming (BECMG), and temporary (TEMPO). 

“FM” is used when a rapid and significant change, 

usually within an hour, is expected. “BECMG” is used 

when a gradual change in the weather is expected over 

a period of no more than 2 hours. “TEMPO” is used 

for temporary fluctuations of weather, expected to last 

less than one hour. 

10. Probability forecast—a given percentage that describes 

the probability of thunderstorms and precipitation 

occurring in the coming hours. This forecast is not 

used for the first 6 hours of the 24-hour forecast.

Example:

TAF

KPIR 111130Z 111212 15012KT P6SM BKN090

TEMPO 1214 5SM BR

FM1500 16015G25KT P6SM SCT040 BKN250

FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 

3SM TSRA BKN030CB

FM0400 1408KT P6SM SCT040 OVC080

TEMPO 0408 3SM TSRA OVC030CB

BECMG 0810 32007KT=

Explanation:

Routine TAF for Pierre, South Dakota...on the 11th day 

of the month, at 1130Z...valid for 24 hours from 1200Z 

on the 11th to 1200Z on the 12th...wind from 150° at 12 

knots...visibility greater than 6 sm...broken clouds at 9,000 

feet...temporarily, between 1200Z and 1400Z, visibility 5 sm 

in mist...from 1500Z winds from 160° at 15 knots, gusting 

to 25 knots visibility greater than 6 sm...clouds scattered 

at 4,000 feet and broken at 25,000 feet...from 0000Z wind 

from 140° at 12 knots...visibility greater than 6 sm...clouds 

broken at 8,000 feet, overcast at 15,000 feet...between 0000Z 

and 0400Z, there is 40 percent probability of visibility 3 

sm...thunderstorm with moderate rain showers...clouds 

broken at 3,000 feet with cumulonimbus clouds...from 

0400Z...winds from 140° at 8 knots...visibility greater 

than 6 miles...clouds at 4,000 scattered and overcast at 

8,000...temporarily between 0400Z and 0800Z...visibility 3 

miles...thunderstorms with moderate rain showers...clouds 

overcast at 3,000 feet with cumulonimbus clouds...becoming 

between 0800Z and 1000Z...wind from 320° at 7 knots...end 

of report (=).

Area Forecasts (FA)

The FA gives a picture of clouds, general weather conditions, 

and visual meteorological conditions (VMC) expected over 

a large area encompassing several states. There are six areas 

for which area forecasts are published in the contiguous 48 

states. Area forecasts are issued three times a day and are 

valid for 18 hours. This type of forecast gives information 

vital to en route operations, as well as forecast information 

for smaller airports that do not have terminal forecasts.

Area forecasts are typically disseminated in four sections and 

include the following information:

1. Header—gives the location identifier of the source of 

the FA, the date and time of issuance, the valid forecast 

time, and the area of coverage.

Example:

DFWC FA 120945

SYNOPSIS AND VFR CLDS/WX

SYNOPSIS VALID UNTIL 130400

CLDS/WX VALID UNTIL 122200...OTLK VALID

122200-130400

OK TX AR LA MS AL AND CSTL WTRS

Explanation:

The area forecast shows information given by Dallas Fort 

Worth, for the region of Oklahoma, Texas, Arkansas, 

Louisiana, Mississippi, and Alabama, as well as a portion of the 

Gulf coastal waters. It was issued on the 12th day of the month 

at 0945. The synopsis is valid from the time of issuance until 

0400 hours on the 13th. VFR clouds and weather information 

on this area forecast are valid until 2200 hours on the 12th and 

the outlook is valid until 0400 hours on the 13th.
12-12

2. Precautionary statements—IFR conditions, mountain 

obscurations, and thunderstorm hazards are described 

in this section. Statements made here regarding height 

are given in MSL, and if given otherwise, AGL or 

ceiling (CIG) will be noted.

Example:

SEE AIRMET SIERRA FOR IFR CONDS AND MTN 

OBSCN.

TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND 

IFR CONDS.

NON MSL HGTS DENOTED BYAGL OR CIG.

Explanation:

The area forecast covers VFR clouds and weather, so the 

precautionary statement warns that AIRMET Sierra should 

be referenced for IFR conditions and mountain obscuration. 

The code TS indicates the possibility of thunderstorms 

and implies there may be occurrences of severe or greater 

turbulence, severe icing, low-level wind shear, and IFR 

conditions. The final line of the precautionary statement alerts 

the user that heights, for the most part, are MSL. Those that 

are not MSL will be AGL or CIG.

3. Synopsis—gives a brief summary identifying the 

location and movement of pressure systems, fronts, 

and circulation patterns.

Example:

SYNOPSIS...LOW PRES TROF 10Z OK/TX PNHDL 

AREA FCST MOV EWD INTO CNTRL-SWRN OK BY 

04Z. WRMFNT 10Z CNTRL OK-SRN AR-NRN MS FCST 

LIFT NWD INTO NERN OK-NRN AR EXTRM NRN MS 

BY 04Z.

Explanation:

As of 1000Z, there is a low pressure trough over the 

Oklahoma and Texas panhandle area, which is forecast 

to move eastward into central southwestern Oklahoma 

by 0400Z. A warm front located over central Oklahoma, 

southern Arkansas, and northern Mississippi at 1000Z is 

forecast to lift northwestward into northeastern Oklahoma, 

northern Arkansas, and extreme northern Mississippi by 

0400Z.

4. VFR Clouds and Weather—This section lists expected 

sky conditions, visibility, and weather for the next 12 

hours and an outlook for the following 6 hours.

Example:

S CNTRL AND SERN TX

AGL SCT-BKN010. TOPS 030. VIS 3-5SM BR. 14-16Z 

BECMG AGL SCT030. 19Z AGL SCT050.

OTLK...VFR

OK

PNDLAND NW...AGL SCT030 SCT-BKN100.

TOPS FL200.

15Z AGL SCT040 SCT100. AFT 20Z SCT TSRA DVLPG..

FEW POSS SEV. CB TOPS FL450.

OTLK...VFR

Explanation:

In south central and southeastern Texas, there is a scattered 

to broken layer of clouds from 1,000 feet AGL with tops at 

3,000 feet, visibility is 3 to 5 sm in mist. Between 1400Z and 

1600Z, the cloud bases are expected to increase to 3,000 feet 

AGL. After 1900Z, the cloud bases are expected to continue 

to increase to 5,000 feet AGL and the outlook is VFR.

In northwestern Oklahoma and panhandle, the clouds are 

scattered at 3,000 feet with another scattered to broken layer 

at 10,000 feet AGL, with the tops at 20,000 feet. At 1500 

Z, the lowest cloud base is expected to increase to 4,000 

feet AGL with a scattered layer at 10,000 feet AGL. After 

2000Z, the forecast calls for scattered thunderstorms with 

rain developing and a few becoming severe; the CB clouds 

will have tops at flight level 450 or 45,000 feet MSL.

It should be noted that when information is given in the area 

forecast, locations may be given by states, regions, or specific 

geological features such as mountain ranges. Figure 12-12

shows an area forecast chart with six regions of forecast, 

states, regional areas, and common geographical features.

Inflight Weather Advisories

Inflight weather advisories, which are provided to en route 

aircraft, are forecasts that detail potentially hazardous 

weather. These advisories are also available to pilots prior to 

departure for flight planning purposes. An inflight weather 

advisory is issued in the form of either an AIRMET, SIGMET, 

or convective SIGMET.

AIRMET

AIRMETs (WAs) are examples of inflight weather advisories 

that are issued every 6 hours with intermediate updates 

issued as needed for a particular area forecast region. The 

information contained in an AIRMET is of operational 

interest to all aircraft, but the weather section concerns 

phenomena considered potentially hazardous to light aircraft 

and aircraft with limited operational capabilities.

An AIRMET includes forecast of moderate icing, moderate 

turbulence, sustained surface winds of 30 knots or greater, 

widespread areas of ceilings less than 1,000 feet and/or 

visibilities less than three miles, and extensive mountain 

obscurement.
12-13

South

Delta Area

NW NE North

Central

SW SE

NW NE

Ozarks

Boot

Heel

SW Missouri Lakes Area

Lake of the Ozarks Area

Extreme

SRN

IL

SW SE

Central

NW NE

NW NE

SW SE

Central

Iowa

SW SE

Extrm SE

NW NE

Northeast Lakes Region

Upper Mississippi Valley

Arrowhead

Lake Superior

Shoreline

WRN Upper MI

Cntrl

Upper

MI

ERN Upper MI

Door PeninsulaMackinac Area

NRN Highlands

The

Thumb

Saginaw

Valley Grand

Valley

Irish Hills

Near Lake

Mi Extrm

N

NW NE

SW SE

Near Ohio River

SW

SE

West

N

Cntrl

Northern

Southern

Cntrl

EastNE

West

Middle East Appalachian Mountains

SE

NW NE Along Ohio River

Extrm

NW

SWRN

Southern

W

Cntrl E

Cntrl

N Third

S

Third

Near Lake Erie

Lee Lake Erie

Lower Great

Lakes Basin Extrm NW

Allegheny Plateau

NW

SW S

Cntrl

NE

SE

N

Cntrl

Lee Lake Ontario

NRN

SRN NE

Eastern

Shore Coastal

Waters

NE

NW

SW SE

Coastal Plain

NE

SE

Piedmont

West

Mtns

of

SC

Coastal Plain

NW

Mtns

Hills

of

Alabama

West

Cntrl

East

Cntrl

Extrm

SE Extrm Southern

Georgia Mobile

Area

FL W 85

Extrm

North

North

Central

Apalachee

Bay South

Extrm

South Upper

Keys

Lower Keys

Gulf Stream

Florida Straits

Coastal

Waters

Catskill

Mtns

E Cntrl

Cape Cod

Coastal Plains

Hudson Valley

Mohawk

Valley

West of

Catskills

Adirondack

Mtns

Champlain

Valley

Green

Mtns

N of Catskills White Mtns NW NE

Coastal Sectio

SE

n SW

MN

IA

MI

IL IN

MO

AR

LA

MS

AL

TN

GA

FL

SC

NC

VA

MD

DC

NJ

OH

WI

WV

PA

NY

ME

VT

NH MA

RI

CT

Coastal Waters–from

coast outward to the

flight information

region border

SW

SE

Northern

NE

Mtns

Central

Strait of Juan De Fuca

Olympic Mtns

Sacramento

Valley

Northwest

North Central

South Central

Lower

Rio 

Grande

Valley

Lower

Coastal

Plain

Mid Coastal

Plain Upper Coastal

Plain

Northwest

Texas

Puget

Sound

Cascade Mtns

Cascade Mtns

of Cascades 

Mtns

NE WA

Columbia

Basin Interior

Valley

Columbia Gorge Blue

Mtns

Wallowa

Mtns

Mtns of

NE OR

Costal Range

Willamette Valley

Coast and

Costal Valley

High Plateau East Slopes

WA

OR

Shasta

Siskiyous

NE CA

NRN

Sierra

Mtns

Coastal Mtns and Valleys

San Joaquin

Valley

SRN

Sierra

Mtns

Coastal Mtns and Valleys

Western

Nevada

Eastern

Nevada

Coastal

Areas

Death

Valley

Lake Tahoe

Lake

Mead

Lake

Mojave

Mojave

Desert

Antelope

Valle Coastal y

Range

SRN

Deserts

Santa

Barbara

Channel

Santa Monica

Bay

Coastal Plain

Gulf of

Santa Catalina

Coacnella

and

Imperial

Valleys

Great

Basin

Colorado River Valley

Gilariver Valley

Mogollon Rim

Chiricahua

Mtns

White

Mtns

Little

Colorado

Valley

Grand Canyon

Four

Corners

Area

Extrm

SW

Uinta Basin

S Cntrl

Mtns

Great

Salt

Lake

Wasatch Mtns

We

V

s

a

t Central

lleys

San Juan

Mtns

NW

Cntrl

Colorado

Mtns

So Platte Valley

NE

Palmer Lake Ridge

or Divide

Eastern Plains

Lower Arkansas Valley

SE

San Luis

Valley

North Park

Rio Grande Valley

Continental Divide

Sacremento

Mtns

Sangre De Cristo

Mtns

Eastern

New Mexico Eastern

Plains

Green River

Basin

So Central

Mtns

SW

WY

Laramie Mtns

N Platte River Val

SE ley

WY

Black

Hills

NE WY

Big Horn Mtns Big Horn

Basin Wind River Mtns

Teton

Mtns

Snake River Valley

Central

Mtns

(Sawtooth)

Yellowstone

Park

Bitterroot Range

Flathead Valley

East

Slopes of

Cont Dvd

SWRN

Mtns

Fort Peck Reservoir

Wind River

Basin

E of Cont Dvd

Pecos River

West of

Pecos

Big

A

Bend

rea

East of

Pecos

Southwest

Panhandle

Northeast

Southeast

Coastal Bend

Southwest Southeast

Panhandle

Northeast

High Plains

Flint

Hills

Marais des Cygnes Basin

Kansas River Valley

Blue River Valley Lower

Republican

Valley

Cheyenne River

James

River

NE Lakes

Region

Rosebud

Country

Pine

Ridge Area

Big Bend

Reservoir

North of

Black

Hills

Lake Lewis and Francis Case Clark

Dame 

Reservoir

Missouri

Slope

Souris

River Valley

Sand Hills

Central Nebraska

Nebraska

pan

Handle

Platte River Basin

SE

NE

CA

NV

ID

MT

ND

SD

NE

KS

OK

TX

WY

UT

CO

AZ

NM

Lake Powell

Red River Valley

Lower Mississippi Valley

CHI Chicago BOS Boston

MIA Miami SFO

San Francisco

SLC Salt Lake City

DFW

Dallas/Fort Worth

Lake Mich Shoreline

Figure 12-12. Area forecast region map.

Each AIRMET bulletin has a fixed alphanumeric designator, 

numbered sequentially for easy identification, beginning with 

the first issuance of the day. Sierra is the AIRMET code used 

to denote IFR and mountain obscuration; Tango is used to 

denote turbulence, strong surface winds, and low-level wind 

shear; and Zulu is used to denote icing and freezing levels.

Example:

DFWTWA 241650

AIRMET TANGO UPDT 3 FOR TURBC... STG

SFC WINDS AND LLWS VALID UNTIL 242000

AIRMET TURBC... OK TX...UPDT

FROM OKC TO DFW TO SAT TO MAF TO CDS

TO OKC OCNL MDT TURBC BLO 60 DUE TO

STG AND GUSTY LOW LVL WINDS. CONDS

CONTG BYD 2000Z

Explanation:

This AIRMET was issued by Dallas–Fort Worth on the 

24th day of the month, at 1650Z time. On this third update, 

the AIRMET Tango is issued for turbulence, strong surface 

winds, and low-level wind shear until 2000Z on the same 

day. The turbulence section of the AIRMET is an update 

for Oklahoma and Texas. It defines an area from Oklahoma 

City to Dallas, Texas, to San Antonio, to Midland, Texas, 

to Childress, Texas, to Oklahoma City that will experience 

occasional moderate turbulence below 6,000 feet due to 

strong and gusty low-level winds. It also notes that these 

conditions are forecast to continue beyond 2000Z.

SIGMET

SIGMETs (WSs) are inflight advisories concerning nonconvective weather that is potentially hazardous to all 

aircraft. They report weather forecasts that include severe 

icing not associated with thunderstorms, severe or extreme 

turbulence or clear air turbulence (CAT) not associated with 

thunderstorms, dust storms or sandstorms that lower surface 

or inflight visibilities to below three miles, and volcanic 

ash. SIGMETs are unscheduled forecasts that are valid for 

4 hours, but if the SIGMET relates to hurricanes, it is valid 

for 6 hours.

A SIGMET is issued under an alphabetic identifier, from 

November through Yankee, excluding Sierra and Tango. 

The first issuance of a SIGMET is designated as an Urgent 

Weather SIGMET (UWS). Reissued SIGMETs for the same 

weather phenomenon are sequentially numbered until the 

weather phenomenon ends.
12-14

FD KWBC 151640

BASED ON 151200Z DATA

VALID 151800Z FOR USE 1700-2100Z 

TEMPS NEGATIVE ABV 24000

FD 3000 6000 9000 12000 18000 24000 30000

AMA 2714 2725+00 2625-04 2531-15 2542-27 265842

DEN 2321-04 2532-08 2434-19 2441-31 235347

Figure 12-13. Winds and temperature aloft report.

Example:

SFOR WS 100130

SIGMET ROME02 VALID UNTIL 100530

OR WA

FROM SEA TO PDT TO EUG TO SEA

OCNL MOGR CAT BTN 280 AND 350 EXPCD

DUE TO JTSTR. 

CONDS BGNG AFT 0200Z CONTG BYD 0530Z .

Explanation:

This is SIGMET Romeo 2, the second issuance for this 

weather phenomenon. It is valid until the 10th day of the 

month at 0530Z time. This SIGMET is for Oregon and 

Washington, for a defined area from Seattle to Portland to 

Eugene to Seattle. It calls for occasional moderate or greater 

clear air turbulence between 28,000 and 35,000 feet due to the 

location of the jet stream. These conditions will be beginning 

after 0200Z and will continue beyond the forecast scope of 

this SIGMET of 0530Z.

Convective Significant Meteorological Information 

(WST)

A convective SIGMET (WST) is an inflight weather advisory 

issued for hazardous convective weather that affects the safety 

of every flight. Convective SIGMETs are issued for severe 

thunderstorms with surface winds greater than 50 knots, hail 

at the surface greater than or equal to 3⁄4 inch in diameter, or 

tornadoes. They are also issued to advise pilots of embedded 

thunderstorms, lines of thunderstorms, or thunderstorms with 

heavy or greater precipitation that affect 40 percent or more 

of a 3,000 square foot or greater region.

Convective SIGMETs are issued for each area of the 

contiguous 48 states but not Alaska or Hawaii. Convective 

SIGMETs are issued for the eastern (E), western (W), and 

central (C) United States. Each report is issued at 55 minutes 

past the hour, but special reports can be issued during the 

interim for any reason. Each forecast is valid for 2 hours. They 

are numbered sequentially each day from 1–99, beginning 

at 00Z time. If no hazardous weather exists, the convective 

SIGMET is still issued; however, it states “CONVECTIVE 

SIGMET...NONE.”

Example:

MKCC WST 221855

CONVECTIVE SIGMET 21C

VALID UNTIL 2055

KS OK TX

VCNTY GLD-CDS LINE

NO SGFNT TSTMS RPRTD

LINE TSTMS DVLPG BY 1955Z WILL MOV EWD

30-35 KT THRU 2055Z

HAIL TO 2 IN PSBL

Explanation:

The WST indicates this report is a convective SIGMET. The 

current date is the 22nd of the month and it was issued at 

1855Z. It is convective SIGMET number 21C, indicating that 

it is the 21st consecutive report issued for the central United 

States. This report is valid for 2 hours until 2055Z time. The 

convective SIGMET is for an area from Kansas to Oklahoma 

to Texas, in the vicinity of a line from Goodland, Kansas, 

to Childress, Texas. No significant thunderstorms are being 

reported, but a line of thunderstorms will develop by 1955 

Zulu time and will move eastward at a rate of 30–35 knots 

through 2055Z. Hail up to 2 inches in size is possible with 

the developing thunderstorms.

Winds and Temperature Aloft Forecast (FD)

Winds and temperatures aloft forecasts (FD) provide wind 

and temperature forecasts for specific locations in the 

contiguous United States, including network locations in 

Hawaii and Alaska. The forecasts are made twice a day 

based on the radiosonde upper air observations taken at 

0000Z and 1200Z.

Through 12,000 feet are true altitudes and above 18,000 feet 

are pressure altitudes. Wind direction is always in reference to 

true north and wind speed is given in knots. The temperature 

is given in degrees Celsius. No winds are forecast when 

a given level is within 1,500 feet of the station elevation. 

Similarly, temperatures are not forecast for any station within 

2,500 feet of the station elevation.

If the wind speed is forecast to be greater than 100 knots but 

less than 199 knots, the computer adds 50 to the direction 

and subtracts 100 from the speed. To decode this type of data 

group, the reverse must be accomplished. For example, when 

the data appears as “731960,” subtract 50 from the 73 and 

add 100 to the 19, and the wind would be 230° at 119 knots 

with a temperature of –60 °C. If the wind speed is forecast to 

be 200 knots or greater, the wind group is coded as 99 knots. 

For example, when the data appears as “7799,” subtract 50 

from 77 and add 100 to 99, and the wind is 270° at 199 knots 

or greater. When the forecast wind speed is calm or less than 

5 knots, the data group is coded “9900,” which means light 

and variable. [Figure 12-13]
12-15

Figure 12-14. Surface analysis chart.

Explanation of Figure 12-13:

The heading indicates that this FD was transmitted on the 15th 

of the month at 1640Z and is based on the 1200Z radiosonde. 

The valid time is 1800Z on the same day and should be 

used for the period between 1700Z and 2100Z. The heading 

also indicates that the temperatures above 24,000 feet MSL 

are negative. Since the temperatures above 24,000 feet are 

negative, the minus sign is omitted. 

A four-digit data group shows the wind direction in reference 

to true north and the wind speed in knots. The elevation at 

Amarillo, Texas (AMA) is 3,605 feet, so the lowest reportable 

altitude is 6,000 feet for the forecast winds. In this case, 

“2714” means the wind is forecast to be from 270° at a speed 

of 14 knots.

A six-digit group includes the forecast temperature aloft. 

The elevation at Denver (DEN) is 5,431 feet, so the lowest 

reportable altitude is 9,000 feet for the winds and temperature 

forecast. In this case, “2321-04” indicates the wind is forecast 

to be from 230° at a speed of 21 knots with a temperature 

of –4 °C.

Weather Charts

Weather charts are graphic charts that depict current or 

forecast weather. They provide an overall picture of the 

United States and should be used in the beginning stages of 

flight planning. Typically, weather charts show the movement 

of major weather systems and fronts. Surface analysis, 

weather depiction, and radar summary charts are sources of 

current weather information. Significant weather prognostic 

charts provide an overall forecast weather picture.

Surface Analysis Chart

The surface analysis chart depicts an analysis of the current 

surface weather. [Figure 12-14] This chart is a computer 

prepared report that is transmitted every 3 hours and covers 

the contiguous 48 states and adjacent areas. A surface analysis 

chart shows the areas of high and low pressure, fronts, 

temperatures, dew points, wind directions and speeds, local 

weather, and visual obstructions.

Surface weather observations for reporting points across 

the United States are also depicted on this chart. Each of 

these reporting points is illustrated by a station model. 

[Figure 12-15] A station model includes:

• Type of observation—a round model indicates an 

official weather observer made the observation. A 

square model indicates the observation is from an 

automated station. Stations located offshore give data 

from ships, buoys, or offshore platforms.

• Sky cover—the station model depicts total sky cover 

and is shown as clear, scattered, broken, overcast, or 

obscured/partially obscured.

• Clouds—represented by specific symbols. Low cloud 

symbols are placed beneath the station model, while 

middle and high cloud symbols are placed directly 

above the station model. Typically, only one type of 

cloud will be depicted with the station model.
12-16

1. Total sky cover: Overcast

2. Temperature/Dew point: 34 °F/32 °F

3. Wind: From the northwest at 20 knots (relative to true north)

4. Present weather: Continuous light snow

5. Predominant low, middle, high cloud reported: Strato fractus or cumulus, fractus of bad weather, altocumulus in patches

 and dense cirrus

6. Sea level pressure: 1014.7 millibars (mb)

 Note: Pressure is always shown in 3 digits to the nearest tenth of a millibar. 

 For 1,000 mb or greater, prefix a “10” to the 3 digits 

 For less than 1,000 mb, prefix a “9” to the 3 digits 

7. Pressure change in past 3 hours: Increased steadily or unsteadily by 2.8 mb

8. 6-hour precipitation: 45 hundredths of an inch. The amount is given to the nearest hundredth of an inch.

Examples of Wind Speed and Direction Plots

Calm NE/5 kts SW/10 kts N/15 kts N/50 kts S/60 kts

147

28 /

34

32

**

.45

Pressure change in past 3 hours

Pressure tendency

6 Hour precipitation

Sea level pressure

Middle cloud type

Wind speed

Wind direction

Temperature

Total sky cover High cloud type

Present weather

Dew point

Low cloud type

Figure 12-15. Sample station model and weather chart symbols.

• Sea level pressure—given in three digits to the nearest 

tenth of a millibar (mb). For 1,000 mbs or greater, 

prefix a 10 to the three digits. For less than 1,000 mbs, 

prefix a 9 to the three digits.

• Pressure change/tendency—pressure change in tenths 

of mb over the past 3 hours. This is depicted directly 

below the sea level pressure.

• Precipitation—a record of the precipitation that has 

fallen over the last 6 hours to the nearest hundredth 

of an inch.

• Dew point—given in degrees Fahrenheit. 

• Present weather—over 100 different weather symbols 

are used to describe the current weather.

• Temperature—given in degrees Fahrenheit.

• Wind—true direction of wind is given by the wind 

pointer line, indicating the direction from which the 

wind is coming. A short barb is equal to 5 knots of 

wind, a long barb is equal to 10 knots of wind, and a 

pennant is equal to 50 knots.

Weather Depiction Chart

A weather depiction chart details surface conditions as 

derived from METAR and other surface observations. The 

weather depiction chart is prepared and transmitted by 

computer every 3 hours beginning at 0100Z time, and is valid 

at the time of the plotted data. It is designed to be used for 

flight planning by giving an overall picture of the weather 

across the United States. [Figure 12-16]

This type of chart typically displays major fronts or areas 

of high and low pressure. The weather depiction chart 

also provides a graphic display of IFR, VFR, and MVFR 

(marginal VFR) weather. Areas of IFR conditions (ceilings 

less than 1,000 feet and visibility less than three miles) are 

shown by a hatched area outlined by a smooth line. MVFR 

regions (ceilings 1,000 to 3,000 feet, visibility 3 to 5 miles) 

are shown by a nonhatched area outlined by a smooth line. 

Areas of VFR (no ceiling or ceiling greater than 3,000 feet 

and visibility greater than five miles) are not outlined.
12-17

Figure 12-16. Weather depiction chart.

Weather depiction charts show a modified station model that 

provides sky conditions in the form of total sky cover, cloud 

height or ceiling, weather, and obstructions to visibility, but 

does not include winds or pressure readings like the surface 

analysis chart. A bracket ( ] ) symbol to the right of the station 

indicates the observation was made by an automated station. 

A detailed explanation of a station model is depicted in the 

previous discussion of surface analysis charts.

Radar Summary Chart

A radar summary chart is a graphically depicted collection 

of radar weather reports (SDs). [Figure 12-17] The chart 

is published hourly at 35 minutes past the hour. It displays 

areas of precipitation, as well as information regarding the 

characteristics of the precipitation. [Figure 12-18] A radar 

summary chart includes:

• No information—if information is not reported, the 

chart will say “NA.” If no echoes are detected, the 

chart will say “NE.”

• Precipitation intensity contours—intensity can be 

described as one of six levels and is shown on the 

chart by three contour intervals.

• Height of tops—the heights of the echo tops are given 

in hundreds of feet MSL.

• 

Movement of cells—individual cell movement is 

indicated by an arrow pointing in the direction of 

movement. The speed of movement in knots is the 

number at the top of the arrow head. “LM” indicates 

little movement.

• Type of precipitation—the type of precipitation is 

marked on the chart using specific symbols. These 

symbols are not the same as used on the METAR 

charts.

• Echo configuration—echoes are shown as being areas, 

cells, or lines.

• Weather watches—severe weather watch areas for 

tornadoes and severe thunderstorms are depicted by 

boxes outlined with heavy dashed lines.

The radar summary chart is a valuable tool for preflight 

planning. It does, however, contain several limitations 

for the usage of the chart. This chart depicts only areas of 

precipitation. It will not show areas of clouds and fog with 

no appreciable precipitation, or the height of the tops and 

bases of the clouds. Radar summary charts are a depiction 

of current precipitation and should be used in conjunction 

with current METAR and weather forecasts. 
12-18

Figure 12-17. Radar summary chart.

Symbol Meaning

R

RW

S

SW

T

NA

NE

OM

 35

LM

WS999

WT210

SLD

Rain

Rain shower

Snow

Snow shower

Thunderstorm

Not available

No echoes

Out for maintenance

Cell movement to the northeast at 35 knots

Little movement

Severe thunderstorm watch number 999

Tornado watch number 210

8/10 or greater coverage in a line

Line of echoes

Figure 12-18. Intensity levels, contours, and precipitation type 

symbols.

Significant Weather Prognostic Charts

Significant weather prognostic charts are available for lowlevel significant weather from the surface to FL 240 (24,000 

feet), also referred to as the 400 mb level, and high-level 

significant weather from FL 250 to FL 600 (25,000 to 60,000 

feet). The primary concern of this discussion is the low-level 

significant weather prognostic chart.

The low-level chart comes in two forms: the 12– and 24–hour 

forecast chart, and the 36- and 48-hour surface forecast chart. 

The first chart is a four-panel chart that includes 12– and 24–

hour forecasts for significant weather and surface weather. 

Charts are issued four times a day at 0000Z, 0600Z, 1200Z, 

and 1800Z. The valid time for the chart is printed on the 

lower left corner of each panel.

The upper two panels show forecast significant weather, 

which may include nonconvective turbulence, freezing levels, 

and IFR or MVFR weather. Areas of moderate or greater 

turbulence are enclosed in dashed lines. Numbers within these 

areas give the height of the turbulence in hundreds of feet 

MSL. Figures below the line show the anticipated base, while 

figures above the line show the top of the zone of turbulence. 

Also shown on this panel are areas of VFR, IFR, and MVFR. 

IFR areas are enclosed by solid lines, MVFR areas are 

enclosed by scalloped lines, and the remaining, unenclosed 

area is designated VFR. Zigzag lines and the letters “SFC” 

indicate freezing levels in that area are at the surface. Freezing 

level height contours for the highest freezing level are drawn 

at 4,000-foot intervals with dashed lines. 
12-19

Figure 12-19. Significant weather prognostic chart and legend (inset).

ATC Radar Weather Displays 

Although ATC systems cannot always detect the presence 

or absence of clouds, they can often determine the intensity 

of a precipitation area, but the specific character of that area 

(snow, rain, hail, VIRGA, etc.) cannot be determined. For 

this reason, ATC refers to all weather areas displayed on ATC 

radar scopes as “precipitation.” 

ARTCC facilities normally use a Weather and Radar 

Processor (WARP) to display a mosaic of data obtained 

from multiple NEXRAD sites. There is a time delay between 

actual conditions and those displayed to the controller. The 

precipitation data on the ARTCC controller’s display could 

be up to 6 minutes old. The WARP processor is only used 

in ARTCC facilities. All ATC facilities using radar weather 

processors with the ability to determine precipitation 

intensity, describe the intensity to pilots as: 

• Light,

• Moderate,

• Heavy, or

• Extreme.

The lower two panels show the forecast surface weather and 

depicts the forecast locations and characteristics of pressure 

systems, fronts, and precipitation. Standard symbols are used 

to show fronts and pressure centers. Direction of movement 

of the pressure center is depicted by an arrow. The speed 

in knots is shown next to the arrow. In addition, areas of 

forecast precipitation and thunderstorms are outlined. Areas of 

precipitation that are shaded indicate at least one-half of the area 

is being affected by the precipitation. Unique symbols indicate 

the type of precipitation and the manner in which it occurs.

Figure 12-19 depicts a typical significant weather prognostic 

chart as well as the symbols typically used to depict 

precipitation. Prognostic charts are an excellent source of 

information for preflight planning; however, this chart should 

be viewed in light of current conditions and specific local 

area forecasts.

The 36- and 48-hour significant weather prognostic chart 

is an extension of the 12- and 24-hour forecast. It provides 

information regarding surface weather forecasts and includes 

a discussion of the forecast. This chart is issued twice a day. 

It typically contains forecast positions and characteristics 

of pressure patterns, fronts, and precipitation. An example 

of a 36- and 48-hour surface prognostic chart is shown in 

Figure 12-20. 
12-20

Figure 12-20. 36- (top) and 48-hour (bottom) surface prognostic chart.
12-21

Figure 12-21. Information page.

When the WARP is not available, a second system, the 

narrowband Air Route Surveillance Radar (ARSR) can 

display two distinct levels of precipitation intensity that will 

be described to pilots as “MODERATE and “HEAVY TO 

EXTREME.” 

ATC facilities that cannot display the intensity levels of 

precipitation due to equipment limitations will describe the 

location of the precipitation area by geographic position, 

or position relative to the aircraft. Since the intensity level 

is not available, the controller will state “INTENSITY 

UNKNOWN.” 

ATC radar is not able to detect turbulence. Generally, turbulence 

can be expected to occur as the rate of rainfall or intensity of 

precipitation increases. Turbulence associated with greater rates 

of rainfall/precipitation will normally be more severe than any 

associated with lesser rates of rainfall/precipitation. Turbulence 

should be expected to occur near convective activity, even in 

clear air. Thunderstorms are a form of convective activity that 

imply severe or greater turbulence. Operation within 20 miles 

of thunderstorms should be approached with great caution, 

as the severity of turbulence can be much greater than the 

precipitation intensity might indicate. 

Weather Avoidance Assistance

To the extent possible, controllers will issue pertinent 

information on weather and assist pilots in avoiding such 

areas when requested. Pilots should respond to a weather 

advisory by either acknowledging the advisory or by 

acknowledging the advisory and requesting an alternative 

course of action as follows: 

• Request to deviate off course by stating the number of 

miles and the direction of the requested deviation. 

 • Request a new route to avoid the affected area. 

 • Request a change of altitude. 

 • Request radar vectors around the affected areas. 

It should be remembered that the controller’s primary 

function is to provide safe separation between aircraft. Any 

additional service, such as weather avoidance assistance, can 

only be provided to the extent that it does not detract from the 

primary function. It’s also worth noting that the separation 

workload is generally greater than normal when weather 

disrupts the usual flow of traffic. ATC radar limitations and 

frequency congestion may also be a factor in limiting the 

controller’s capability to provide additional service.

Electronic Flight Displays (EFD) /MultiFunction Display (MFD) Weather 

Many aircraft manufacturers now include satellite weather 

services with new electronic flight display (EFD) systems. 

EFDs give a pilot access to many of the satellite weather 

services available. 

Products available to a pilot on the display pictured in 

Figure 12-21 are listed as follows. The letters in parentheses 

indicate the soft key to press in order to access the data.
12-22

Figure 12-22. List of weather products and the expiration times 

of each.

NEXRAD

RAIN

MIX

SNOW

H

E

A

V

Y

L

I

G

H

T

SIGMET

AIRMET

__/__ __:__

__/__ __:__

NORTH UP

• Graphical NEXRAD data (NEXRAD)

• Graphical METAR data (METAR)

• Textual METAR data

• Textual terminal aerodrome forecasts (TAF)

• City forecast data

• Graphical wind data (WIND)

• Graphical echo tops (ECHO TOPS)

• Graphical cloud tops (CLD TOPS)

• Graphical lightning strikes (LTNG)

• Graphical storm cell movement (CELL MOV)

• NEXRAD radar coverage (information displayed with 

the NEXRAD data)

• SIGMETs/AIRMETs (SIG/AIR)

• Surface analysis to include city forecasts (SFC)

• County warnings (COUNTY)

• Freezing levels (FRZ LVL)

• Hurricane track (CYCLONE)

• Temporary flight restrictions (TFR)

Pilots must be familiar with any EFD or MFD used and the 

satellite weather products available on the display.

Weather Products Age and Expiration

The information displayed using a satellite weather link is near 

real time but should not be thought of as instantaneous upto-date information. Each type of weather display is stamped 

with the age information on the MFD. The time is referenced 

from Zulu when the information was assembled at the ground 

station. The age should not be assumed to be the time when 

the FIS received the information from the satellite.

Two types of weather are displayed on the screen: “current” 

weather and forecast data. Current information is displayed 

by an age while the forecast data has a data stamp in the form 

of “__ / __ __ : __”. [Figure 12-22]

The Next Generation Weather Radar System 

(NEXRAD)

The NEXRAD system is comprised of a series of 159 Weather 

Surveillance Radar–1988 Doppler (WSR-88D) sites situated 

throughout the United States as well as selected oversees sites. 

The NEXRAD system is a joint venture between the United 

States Department of Commerce (DOC), the United States 

Department of Defense, (DOD) as well as the United States 

Department of Transportation (DOT). The individual agencies 

that have control over the system are the NWS, Air Force 

Weather Agency (AFWA) and the FAA. [Figure 12-23]

NEXRAD radar produces two levels of products: level II 

and level III.

Level II Data Products

All NEXRAD level-II data products are available through the 

National Climatic Data Center (NCDC). Level II data consists 

of the three meteorological base data quantities: reflectivity, 

mean radial velocity, and spectrum width.

Level III Data Products

There are 41 products routinely available through the 

NCDC. Level III graphic products are available as digital 

images, color hard copy, gray scale hard copy, or acetate 

overlay copies. This information is then encoded and 

disseminated through the satellite weather system as well 

as other sources.

NEXRAD level III data for up to a 2,000 mile range can be 

displayed. It is important to realize that the radar image is not 

real time and can be up to 5 minutes old. At no time should 

the images be used as storm penetrating radar nor to navigate 

through a line of storms. The images display should only be 

used as a reference. 
12-23

Figure 12-23. NEXRAD radar display.

NEXRAD radar is mutually exclusive of Topographic 

(TOPO), TERRAIN and STORMSCOPE. When 

NEXRAD is turned on, TOPO, TERRAIN, and 

STORMSCOPE are turned off because the colors used to 

display intensities are very similar. 

Lightning information is available to assist when NEXRAD 

is enabled. This presents a more vivid picture of the weather 

in the surrounding area.

In addition to utilizing the soft keys to activate the NEXRAD 

display, the pilot also has the option of setting the desired 

range. It is possible to zoom in on a specific area of the 

display in order to gain a more detailed picture of the radar 

display. [Figure 12-24]

NEXRAD Abnormalities

Although NEXRAD is a compilation of stations across 

the country, there can be abnormalities associated with the 

system. Some of the abnormalities are listed below.

• Ground clutter

• Strobes and spurious radar data

• Sun strobes, when the radar antenna points directly at 

the sun

• Interference from buildings or mountains, which may 

cause shadows

• Military aircraft which deploy metallic dust and may 

reflect the radar signature

NEXRAD Limitations

In addition to the abnormalities listed, the NEXRAD system 

does have some specific limitations. 

Base Reflectivity

The NEXRAD base reflectivity does not provide adequate 

information from which to determine cloud layers or type 

of precipitation with respect to hail versus rain. Therefore, a 

pilot may mistake rain for hail.

In addition, the base reflectivity is sampled at the minimum 

antenna elevation angle. With this minimum angle, an 

individual site cannot depict high altitude storms directly 

over the station. This will leave an area of null coverage if 

an adjacent site does not also cover the affected area.
12-24

Figure 12-24. NEXRAD radar display (500 mile range). The individual color gradients can be easily discerned and interpreted via the 

legend in the upper right corner of the screen. Additional information can be gained by pressing the LEGEND soft key, which displays 

the legend page.

Resolution Display

The resolution of the displayed data will pose additional 

concerns when the range is decreased. The minimum 

resolution for NEXRAD returns is two kilometers. This means 

that when the display range is zoomed in to approximately 

ten miles, the individual square return boxes will be more 

prevalent. Each square will indicate the strongest display 

return within that two kilometer square area.

AIRMET/SIGMET Display

AIRMET/SIGMET information is available for the displayed 

viewing range on the MFD. Some displays are capable of 

displaying weather information for a 2,000 mile range. 

AIRMETS/SIGMETS are displayed by dashed lines on the 

map. [Figure 12-25]

The legend box denotes the various colors used to depict the 

AIRMETs such as icing, turbulence, IFR weather, mountain 

obscuration as well as surface winds. [Figure 12-26] The great 

advantage of the graphically displayed AIRMET/SIGMET 

boundary box is the pilot can see the extent of the area that 

the report covers. The pilot does not need to manually plot the 

points to determine the full extent of the coverage area.

Graphical METARs

METARs can be displayed on the multi-function display. 

Each reporting station that has a METAR/TAF available 

is depicted by a flag from the center of the airport symbol. 

Each flag is color coded to depict the type of weather that 

is currently reported at that station. A legend is available to 

assist users in determining what each flag color represents. 

[Figure 12-27] 

The graphical METAR display shows all available reporting 

stations within the set viewing range. By setting the range 

knob up to a 2,000 mile range, pilots can pan around the 

display map to check the current conditions of various 

airports along the route of flight.

By understanding what each colored flag indicates, a pilot can 

quickly determine where weather patterns display marginal 

weather, IFR, or areas of VFR. These flags make it easy to 

determine weather at a specific airport should the need arise 

to divert from the intended airport of landing.
12-25

Figure 12-25. The AIRMET information box instructs the pilot to press the enter button to gain additional information on the selected area 

of weather. Once the enter soft key (ENT) is depressed, the specific textual information is displayed on the right side of the screen.

Figure 12-26. SIGMET/AIRMET legend display.
12-26

Figure 12-27. Graphical METAR legend display.

Chapter Summary

While no weather forecast is guaranteed to be 100 percent 

accurate, pilots have access to a myriad of weather 

information on which to base flight decisions. Weather 

products available for preflight planning to en route 

information received over the radio or via satellite link 

provide the pilot with the most accurate and up-to-date 

information available. Each report provides a piece of the 

weather puzzle. Pilots must use several reports to get an 

overall picture and gain an understanding of the weather that 

will affect the safe completion of a flight.