Climatic Atlas of te

Delaware River Basin

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1392
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY

Instructions on ordering publications of the U.S. Geological Survey, along with the last offerings, are given in the 

current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological 

Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications 

that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price 

and Availability List" are no longer available.

Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated 

monthly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, 

Box 25425, Denver, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical 

Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry.

Order U.S. Geological Survey publications by mail or over the counter from the offices given below.

BY MAIL

Books

Professional Papers, Bulletins, Water-Supply Papers, 

Techniques of Water-Resources Investigations, Circulars, publications of general interest (such as leaflets, pamphlets, booklets), single copies of periodicals (Earthquakes & Volcanoes, 

Preliminary Determination of Epicenters), and some miscellaneous reports, including some of the foregoing series that have 

gone out of print at the Superintendent of Documents, are 

obtainable by mail from

U.S. Geological Survey, Books and Open-File Reports Section

Federal Center, Box 25425

Denver, CO 80225

Subscriptions to periodicals (Earthquakes & Volcanoes 

and Preliminary Determination of Epicenters) can be obtained 

ONLY from

Superintendent of Documents

U.S. Government Printing Office

Washington, DC 20402

(Check or money order must be payable to Superintendent 

of Documents.)

Maps

For maps, address mail orders to

U.S. Geological Survey, Map Distribution

Federal Center, Box 25286

Denver, CO 80225

Residents of Alaska may order maps from

U.S. Geological Survey, Map Distribution

New Federal Building - Box 12 

101 Twelfth Ave., Fairbanks, AK 99701

OVER THE COUNTER

Books

Books of the U.S. Geological Survey are available over 

the counter at the following U.S. Geological Survey offices, all 

of which are authorized agents of the Superintendent of Documents:

 ANCHORAGE, Alaska-4230 University Dr., Rm. 101

 ANCHORAGE, Alaska-605 West 4th Ave., Rm. G-84

 DENVER, Colorado-Federal Bldg., Rm. 169, 1961 Stout 

St.

 LOS ANGELES, California-Federal Bldg., Rm. 7638, 

300 North Los Angeles St.

 MENLO PARK, California-Bldg. 3, Rm. 3128, 345 Middlefield Rd.

 RESTON, Virginia-National Center, Rm. 1C402, 12201 

Sunrise Valley Dr.

 SALT LAKE CITY, Utah Federal Bldg., Rm. 8105, 125 

South State St.

 SAN FRANCISCO, California-Customhouse, Rm. 504, 

555 Battery St.

 SPOKANE, Washington U.S. Courthouse, Rm. 678, West 

920 Riverside Ave.

 WASHINGTON, DC U.S. Department of the Interior 

Bldg., Rm. 2650, 1849 C St., NW.

Maps

Maps may be purchased over the counter at the U.S. 

Geological Survey offices where books are sold (all addresses in 

above list) and at the following U.S. Geological Survey offices:

 ROLLA, Missouri 1400 Independence Rd.

 FAIRBANKS, Alaska-New Federal Bldg., 101 Twelfth 

Ave.
Climatic Atlas of the 

Delaware River Basin

By CAROL B. JENNER and HARRY F. LINS

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1392

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1991
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names in this publication is for 

d does not imj 

Government

descriptive purposes only and does not imply endorsement by the

U.S. ~

Library of Congress Cataloging in Publication Data

Jenner, Carol B.

Climatic atlas of the Delaware River Basin.

(Geological Survey professional paper ; 1392) Covers the period 1950-1979.

Bibliography: p.

Supt.ofDocs.no.: 119.16:1392

1. Delaware River Watershed (N.Y.-Del. and N.J.)-Climate-Maps. I. Lins, Harry F. II. Title. III. Series.

G1247.D44C8J4 1991 912'. 155169749 85-600149

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225
CONTENTS

	Page

Abstract............................................. 1

Introduction.......................................... 1

Physical Setting.................................... 2

Data Compilation. ................................. 2

Climatic Variability. .................................. 6

Circulation of the Midlatitudes....................... 6

Relation of Upper Air Flow to Surface Weather......... 7

Atmospheric Circulation and Climatic Variability....... 8

Climatic Characteristics of the Delaware River Basin....... 10

Temperature....................................... 10

Average Annual Temperature..................... 12

Average December Temperature................. 14

Average January Temperature.................. 16

Average February Temperature. ................ 18

Average March Temperature................... 20

Average April Temperature. ................... 22

Average May Temperature..................... 24

Average June Temperature..................... 26

Average July Temperature..................... 28

Average August Temperature................... 30

Average September Temperature................ 32

Average October Temperature. ................. 34

Average November Temperature................ 36

Average Winter Temperature...................... 38

Average Spring Temperature...................... 40

Average Summer Temperature.................... 42

Average Fall Temperature........................ 44

Temperature Extremes........................... 46

Heating Degree Days. ............................ 50

Freeze-Free Season.............................. 52

Precipitation....................................... 57

Average Annual Precipitation..................... 58

	Page

Climatic Characteristics of the Delaware River Basin Continued 

Precipitation Continued

Average Annual Precipitation Continued

Average December Precipitation. ................ 60

Average January Precipitation.................. 62

Average February Precipitation................. 64

Average March Precipitation................... 66

Average April Precipitation.................... 68

Average May Precipitation..................... 70

Average June Precipitation..................... 72

Average July Precipitation. .................... 74

Average August Precipitation................... 76

Average September Precipitation. ............... 78

Average October Precipitation. ................. 80

Average November Precipitation. ............... 82

Average Winter Precipitation...................... 84

Average Spring Precipitation...................... 86

Average Summer Precipitation..................... 88

Average Fall Precipitation........................ 90

Snowfall........................................ 92

Precipitation Days ............................... 94

Average Monthly Dew-Point Temperature........... 95

Cloud Cover..................................... 96

Thunderstorm Days.............................. 96

Climatic Water Budget................................ 98

Water Budget for the Delaware River Basin. .............. 99

Potential Evapotranspiration. ........................ 99

Water Surplus..................................... 110

Water Deficit. ..................................... 120

Drought ............................................. 120

Hurricanes and Tropical Storms......................... 124

Selected References.................................... 126

ILLUSTRATIONS

Page

FIGURE 1. Photograph of a portion of the Piedmont Region of the central Delaware River basin. .......................... 2

2-5. Maps showing:

2. Major physiographic features of the Delaware River basin. ......................................... 3

3. Locations of climatological stations used in the Delaware River basin. ............................... 5

4. Typical summer daily 700-millibar height contours above North America. ............................ 6

5. Typical winter daily 700-millibar height contours above North America. ............................. 7

6. Diagram showing the relations between the upper level airflow pattern, paths of cyclonic systems,

and precipitation................................................................................... 7

7. Map showing 500-millibar height contours above North America on January 19, 1977. ......................... 8

8. Map showing the 700-millibar height contours above the Northern Hemisphere on January 1978................. 9

9. Photograph showing the rugged terrain of the Catskill Mountains in the New York portion

of the Delaware River basin......................................................................... 11

10. Graphs showing average annual temperature at four stations in the Delaware River basin,

1950-79.......................................................................................... 12

11. Map showing distribution of average annual temperature in the Delaware River basin. ....................... 13

12. Graphs showing average December temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 14

III
IV CONTENTS

Page

FIGURE 13. Map showing the distribution of average December temperatures in the Delaware River basin. ................. 15

14. Graphs showing average January temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 16

15. Map showing the distribution of average January temperatures in the Delaware River basin. .................. 17

16. Graphs showing average February temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 18

17. Map showing the distribution of average February temperatures in the Delaware River basin. ................. 19

18. Graphs showing average March temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 20

19. Map showing the distribution of average March temperatures in the Delaware River basin. .................... 21

20. Graphs showing average April temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 22

21. Map showing the distribution of average April temperatures in the Delaware River basin. ..................... 23

22. Graphs showing average May temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 24

23. Map showing the distribution of average May temperatures in the Delaware River basin. ..................... 25

24. Graphs showing average June temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 26

25. Map showing the distribution of average June temperatures in the Delaware River basin. ..................... 27

26. Graphs showing average July temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 28

27. Map showing the distribution of average July temperatures in the Delaware River basin. ..................... 29

28. Graphs showing average August temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 30

29. Map showing the distribution of average August temperatures in the Delaware River basin. ................... 31

30. Graphs showing average September temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 32

31. Map showing the distribution of average September temperatures in the Delaware River basin. ................ 33

32. Graphs showing average October temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 34

33. Map showing the distribution of average October temperatures in the Delaware River basin.................... 35

34. Graphs showing average November temperatures at four stations in the Delaware River basin,

1950-79.......................................................................................... 36

35. Map showing the distribution of average November temperatures in the Delaware River basin. ................. 37

36. Graphs showing average winter (December-February) temperatures at four stations

in the Delaware River basin, 1950-79................................................................ 38

37. Map showing the areal distribution of average winter (December-February) temperatures

in the Delaware River basin. ....................................................................... 39

38. Graphs showing average spring (March-May) temperatures at four stations

in the Delaware River basin, 1950-79................................................................ 40

39. Map showing the areal distribution of average spring (March-May) temperatures

in the Delaware River basin. ....................................................................... 41

40. Graphs showing average summer (June-August) temperatures at four stations

in the Delaware River basin, 1950-79................................................................ 42

41. Map showing the areal distribution of average summer (June-August) temperatures

in the Delaware River basin........................................................................ 43

42. Graphs showing average fall (September-November) temperatures at four stations

in the Delaware River basin, 1950-79................................................................ 44

43. Map showing the areal distribution of average fall (September-November) temperatures

in the Delaware River basin. ....................................................................... 45

44-49. Graphs showing:

44. Monthly averaged daily minimum and maximum temperatures at three stations

in the Delaware River basin................................................................ 46

45. Average frequency of days per month of temperatures equal to or above 90 °F and

equal to or below 32 °F at three stations in the Delaware River basin. ............................ 47

46. Average daily maximum and minimum temperatures for January and July,

1950-79, at three stations in the Delaware River basin.......................................... 48

47. Average frequency of days per year of temperatures equal to or above 90 °F and

equal to or below 32 °F at three stations in the Delaware River basin, 1950-79..................... 49

48. Total annual heating degree days for three stations in the Delaware River basin..................... 50

49. Average monthly distribution of heating degree days for three stations

in the Delaware River basin................................................................ 51

50. Graphs showing the daily length of the freeze-free season at four stations in the

Delaware River basin, 1950-79...................................................................... 52
CONTENTS V

Page

FIGURE 51. Graphs showing the daily last minimum temperature in spring and first minimum temperature

in fall at four stations in the Delaware River basin, 1950-79............................................. 53

52-54. Maps showing:

52. Areal distribution of the average date of the last spring minimum temperature

in the Delaware River basin................................................................ 54

53. Areal distribution of the average date of the earliest fall minimum temperature

in the Delaware River basin. ............................................................... 55

54. Areal distribution of the average length of the freeze-free season

in the Delaware River basin. ............................................................... 56

55. Photograph showing northeast-trending ridges at Palmerton, Pa............................................ 57

56. Graphs showing average annual precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 58

57. Map showing the areal distribution of average annual precipitation in the Delaware River basin. ............... 59

58. Graphs showing average December precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 60

59. Map showing the areal distribution of average December precipitation in the

Delaware River basin.............................................................................. 61

60. Graphs showing average January precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 62

61. Map showing the areal distribution of average January precipitation in the Delaware River basin. .............. 63

62. Graphs showing average February precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 64

63. Map showing the areal distribution of average February precipitation in the Delaware River basin. ............. 65

64. Graphs showing average March precipitation at four stations in the Delaware River basin, 1950-79............. 66

65. Map showing the areal distribution of average March precipitation in the Delaware River basin. ............... 67

66. Graphs showing average April precipitation at four stations in the Delaware River basin, 1950-79. ............. 68

67. Map showing the areal distribution of average April precipitation in the Delaware River basin. ................ 69

68. Graphs showing average May precipitation at four stations in the Delaware River basin, 1950-79. .............. 70

69. Map showing the areal distribution of average May precipitation in the Delaware River basin. ................. 71

70. Graphs showing average June precipitation at four stations in the Delaware River basin, 1950-79. ............. 72

71. Map showing the areal distribution of average June precipitation in the Delaware River basin. ................. 73

72. Graphs showing average July precipitation at four stations in the Delaware River basin, 1950-79. .............. 74

73. Map showing the areal distribution of average July precipitation in the Delaware River basin. ................. 75

74. Graphs showing average August precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 76

75. Map showing the areal distribution of average August precipitation in the Delaware River basin. ............... 77

76. Graphs showing average September precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 78

77. Map showing the areal distribution of average September precipitation in the Delaware River basin. ............ 79

78. Graphs showing average October precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 80

79. Map showing the areal distribution of average October precipitation in the Delaware River basin. .............. 81

80. Graphs showing average November precipitation at four stations in the Delaware River basin,

1950-79.......................................................................................... 82

81. Map showing the areal distribution of average November precipitation in the

Delaware River basin. ............................................................................. 83

82. Graphs showing average winter (December-February) precipitation at four stations in the

Delaware River basin, 1950-79...................................................................... 84

83. Map showing the areal distribution of average winter (December-February) precipitation in the

Delaware River basin. ............................................................................. 85

84. Graphs showing average spring (March-May) precipitation at four stations in the

Delaware River basin, 1950-79...................................................................... 86

85. Map showing the areal distribution of average spring (March-May) precipitation in the

Delaware River basin.............................................................................. 87

86. Graphs showing average summer (June-August) precipitation at four stations in the

Delaware River basin, 1950-79...................................................................... 88

87. Map showing the areal distribution of average summer (June-August) precipitation in the

Delaware River basin.............................................................................. 89

88. Graphs showing average fall (September-November) precipitation at four stations in the

Delaware River basin, 1950-79...................................................................... 90

89. Map showing the areal distribution of average fall (September-November) precipitation

in the Delaware River basin........................................................................ 91
VI CONTENTS

Page

FIGURE 90-96. Graphs showing:

90. Total annual snowfall at three stations in the Delaware River basin, 1950-79........................ 92

91. Average monthly snowfall at three stations in the Delaware River basin. ........................... 93

92. Average monthly precipitation days at three stations in the Delaware River basin. ................... 94

93. Average monthly dew-point temperature at three stations in the Delaware River basin. ............... 95

94. Monthly percentage of clear, partly cloudy, and cloudy days for three stations

in the Delaware River basin. ............................................................... 96

95. Annual percentage of clear summer and winter days at three stations in the

Delaware River basin, 1950-79.............................................................. 97

96. Average days per month of thunderstorm occurrence at three stations in the

Delaware River basin. ..................................................................... 98

97. Photograph showing truck gardening in the southern New Jersey coastal plain. .............................. 99

98-107. Maps showing:

98. Average annual potential evapotranspiration in the Delaware River basin. ......................... 100

99. Average March potential evapotranspiration in the Delaware River basin. ......................... 101

100. Average April potential evapotranspiration in the Delaware River basin. .......................... 102

101. Average May potential evapotranspiration in the Delaware River basin. ........................... 103

102. Average June potential evapotranspiration in the Delaware River basin. ........................... 104

103. Average July potential evapotranspiration in the Delaware River basin. ........................... 105

104. Average August potential evapotranspiration in the Delaware River basin. ......................... 106

105. Average September potential evapotranspiration in the Delaware River basin. ...................... 107

106. Average October potential evapotranspiration in the Delaware River basin. ........................ 108

107. Average November potential evapotranspiration in the Delaware River basin. ...................... 109

108. Photograph showing fog in a Delaware River basin valley. ............................................... 110

109. Map showing the areal distribution of average annual water surplus in the Delaware River basin. ............. Ill

110. Graphs showing the average water surplus during winter (December-February) at four stations

in the Delaware River basin, 1950-79............................................................... 112

111. Map showing the areal distribution of average water surplus during winter (December-February)

in the Delaware River basin. ...................................................................... 113

112. Graphs showing the average water surplus during spring (March-May) at four stations in the

Delaware River basin, 1950-79..................................................................... 114

113. Map showing the areal distribution of average water surplus during spring (March-May)

in the Delaware River basin. ...................................................................... 115

114. Graphs showing the average water surplus during summer (June-August) at four stations in the

Delaware River basin, 1950-79..................................................................... 116

115. Map showing the areal distribution of average water surplus during summer (June-August)

in the Delaware River basin. ...................................................................... 117

116. Graphs showing the average water surplus during fall (September-November) at four stations

in the Delaware River basin, 1950-79............................................................... 118

117. Map showing the areal distribution of average water surplus during fall (September-November)

in the Delaware River basin. ...................................................................... 119

118. Graphs showing average annual water deficit at four stations in the Delaware River basin,

1950-79......................................................................................... 120

119. Map showing the areal distribution of average annual water deficit in the Delaware River basin. .............. 121

120. Maps showing annual water deficits in the Delaware River basin during A; 1953, B; 1954, C; 1964,

and D, 1980..................................................................................... 123

121. Map showing the path of hurricanes and tropical storms that affected the Delaware River basin,

1950-79......................................................................................... 125
CONTENTS VII

METRIC CONVERSION FACTORS

For readers who may prefer to use International System of Units (SI) rather than inch-pound units, the conversion factors for the terms 

used in this report are listed below:

Multiply By To obtain

inch (in.) 25.40 millimeter (mm) 

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

1.1507 nautical mile

degree Fahrenheit (°F) °C = 5/9 X (°F - 32) degree Celsius (°C) 

miles per hour (mph) 0.447 meters per second (m/s)

ALTITUDE DATUM

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived 

from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

By CAROL B. JENNER and HARRY F. LINS

ABSTRACT

The Delaware River basin is a diverse physiographic, hydrologic, and 

climatic region. The Delaware River serves as a major source of water 

for nearly 20 million people both in and outside the basin. Questions 

associated outside the variability of climate, the potential for climate 

change, and attendant implications for water resources and supply 

across this region in the coming decades require that there first be 

an appraisal of current climate conditions. To this end, graphs and maps 

for average monthly, seasonal, and annual values of temperature and 

precipitation across the basin during the period 1950-79 have been 

compiled in atlas form. Additional variables, including water budget 

terms, drought, cloud cover, hurricanes, and others have also been 

graphed and mapped.

INTRODUCTION

During the past decade the United States has been 

plagued by a series of anomalous weather events that 

have included record low snowfall for portions of the 

Western mountains, drought in the Northeast, extreme 

precipitation amounts in the Southwest, Great Basin, 

and Northern Great Lakes regions, and record cold and 

snowfall over much of the East. The effects of these 

events have been felt by virtually everyone, and the Nation's agricultural, construction, and industrial sectors 

have been affected adversely.

Variability is a natural part of climate, and the extreme conditions of the last several years may be a part 

of normal climatic variability. They may, however, be a 

manifestation of a slightly changing climate. Most 

climatologists agree that Northern Hemisphere nearsurface temperatures over land increased by about 

1.1 °F from the late 19th century to the 1940's and then 

decreased into the early 1970's (Reitan, 1974; Brinkmann, 1976). Undoubtedly, other climatic variables also 

changed over this period; the precise nature of these 

changes is unknown because of a lack of appropriate data 

collection prior to the late 1940's.

Brinkmann (1979) has analyzed a Northern Hemisphere temperature curve that was determined using 

280 stations having long-term records. When the individual records that contributed to the hemispheric 

curve were analyzed, it was found that some of those 

local records were in phase and some were out of phase 

with the average trend. For most of central and eastern 

North America, the temperature trends have paralleled

the Northern Hemisphere average in a slightly amplified form. However, even the amplified local temperature 

changes seem minor. The importance of seemingly insignificant changes in average temperature is illustrated 

by Bryson and Murray (1977), who state that "an increase of 1 °C in summer temperatures in the northern 

plains can reduce the gross dollar of the spring wheat 

farmers by $131 million. ..."

The importance of climatic information as an input to 

decisionmaking and research is being recognized in 

many fields that previously had ignored such data. Unfortunately, although massive amounts of climatic information are readily available from established government sources, these data are quite often not in a readily 

usable form. The most widely used average values of 

climatic data are climatic "normals." The normal value 

for a climatic parameter (such as January precipitation 

at a station) is defined as the average of that parameter 

over a three-decade period. Climatic normals are revised 

every 10 years. Values currently available for the United 

States cover the 1951-80 period. Although the use of 

average values of climatic parameters may provide sufficient climatological information for some applications 

in other fields, these values often do not give an adequate 

picture of climatic variability. In addition to mean values 

of temperature, precipitation, and so on, some idea of 

extreme values and frequencies of specific events would 

be of great importance in many research and planning 

decisions.

The purpose of this atlas is to present, in a form usable 

by planners, administrators, and policymakers, climatic 

information pertaining to one major watershed within 

the United States the Delaware River basin. Data 

sources for the climatic information are the numerous 

publications of the National Oceanic and Atmospheric 

Administration.

The atlas incorporates several features that typically 

have not been included in other climatic data presentations. It discusses a naturally defined region (a drainage 

basin) rather than a region defined by political boundaries. Climatic variability is discussed with climatic 

average conditions. Finally, although it is impossible and 

impractical to analyze all combinations of climatic 

parameters, associations between temperature and precipitation are presented through the use of water-budget 

analysis.
CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

PHYSICAL SETTING

The Delaware River basin is diverse in topography, 

economic activity, and land use. The basin is approximately 270 mi in length and contains some 7 million 

residents. It includes large industrial complexes and urban areas of extremely high population density as well 

as extensive farmland and wetland areas.

The basin includes portions of low, flat coastal plain 

and rolling Piedmont hills, the striking northeasttrending ridges of the ridge-and-valley section and the 

Catskills, the Poconos, and the Kittatinny Mountains of 

the Allegheny Plateau. Land-use patterns in the region 

are changing in response to urbanization and industrialization and, in part, as a result of changing lifestyles 

and the search for recreational opportunities (fig. 1).

The area is one of conflict between economic and environmental interests (United States Council on Environmental Quality, 1975). The controversy has been 

accentuated in recent years by increasing demands for 

fuel combined with shortages in high-quality fuel supply 

and record cold winters. The critical nature of water 

supply and demand was emphasized in 1980 and again 

in 1984-85 when severe drought conditions developed 

throughout the basin.

Major physiographic features of the Delaware River 

basin are shown in figure 2.

DATA COMPILATION

This atlas of the Delaware River basin focuses on the 

climatic conditions for the 1950-79 period. All average 

values have been calculated for that period. In addition 

to average values for the period, time series of individual 

yearly values are graphed for representative stations. 

Thus average values as well as year-to-year variability 

in climatic parameters are presented. When this atlas 

was being prepared during 1980, severe drought conditions developed in the Delaware River basin. The 1980 

climatic data have been included in the sections on 

drought. Information on the 1984-85 drought, however, 

has not been included. For more information on this 

event, readers are referred to a recent paper by Harkness 

and others (1986).

Data for the atlas came from readily available published sources, mainly climatological data for individual 

States and "Climatological Data, National Summary," 

published by the Environmental Data Service of the 

National Oceanic and Atmospheric Administration 

(NOAA).

For most of the stations included in this report, temperature and precipitation data are collected daily by 

volunteer cooperative observers. At a few selected firstorder stations, usually located at major airports, NOAA 

personnel collect and record a much more comprehenFIGURE 1. Pastureland and agricultural fields west of Philadelphia, Pa., are typical of the Piedmont region of the

central Delaware River basin.
INTRODUCTION

INSET

25

1

50 MILES

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

K: ' " FIGURE 2. Major physiographic features of the Delaware River 

basin. All counties that completely or partially lie within the 

actual watershed boundaries are shown.
CLIMATIC AT1AS OF THE DELAWARE RIVER BASIN

sive set of climatological data. All of this information 

is published on a statewide basis.

Records are generally of high quality. One difficulty 

encountered when using this network was that some of 

the stations had been relocated during the period of 

study. Stations that experienced major changes in location during the 1950-79 period were omitted from this 

study.

Occasionally, station data were missing or unreported 

in the published sources. A station was omitted from this 

analysis if 10 percent or more of the monthly average 

temperature or precipitation values were missing. In the 

case of a station with a few missing values, these values 

were estimated by means of regression relations developed using the appropriate time series of data from nearby stations.

In all, 49 stations provided temperature data, and 82 

stations provided precipitation data. Station locations 

are plotted on figure 3. For the time series plots of yearly 

data, four stations, Georgetown, Del., Indian Mills, N.J., 

Belvidere, N.J., and Hawley, N.Y., were chosen to make 

up a north-south transect within the basin. For depiction 

of more specialized climatological data collected and (or) 

published for first-order stations only, Wilmington, Del., 

Allentown, Pa., and Binghamton, N.Y., were selected.

All contour maps were constructed by the University 

of Wisconsin Cartographic Laboratory using the 

weighted-distance contouring algorithm of the computermapping package WISMAP.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

STATION KEY

Norwich, N.Y.

Kortright 2, N.Y.

Stamford, N.Y.

Lake Delaware, N.Y.

New Kingston, N.Y.

Binghamton WSO AP, N.Y.

Arkville 2W, N.Y.

Deposit, N.Y.

Frost Valley, N.Y.

Claryville, N.Y.

Equinunk 2WNW, N.Y.

Grahamsville, N.Y.

Liberty 1NE, N.Y.

Mohonk Lake, N.Y.

Pleasant Mount 1W, Pa.

Honesdale 4NW, Pa.

Hawley, Pa.

Paupack 2WNW, Pa.

Hollisterville, Pa.

Port Jervis, N.Y.

West Point, N.Y.

Matamoras, Pa.

Wilkes-Barre 4NE, Pa.

Gouldsboro, Pa.

Sussex 1SE, N.J.

Long Pond 2W, Pa.

Newton, N.J.

Charlotteburg Reservoir, N.J.

Freeland, Pa.

Stroudsburg, Pa.

Kresgeville 2W, Pa.

Boonton 1SE, N.J.

Tamaqua 4N Dam, Pa.

Lehighton, Pa.

Belvidere, N.J.

Palmerton, Pa.

Tamaqua, Pa.

Long Valley, N.J.

New Tripoli 4E, Pa.

Allentown WSO AP, Pa.

Claussville, Pa.

42.

43.

44.

45.

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.

Port Clinton, Pa.

Flemington 3E, N.J.

Strausstown, Pa.

Zionsville 3SE, Pa.

Palm 3SE, Pa.

Myerstown, Pa.

Reading 3N, Pa.

Lambert ville, N.J.

Doylestown, Pa.

Hightstown 2W, N.J.

Freehold, N.J.

Graterford IE, Pa.

George School, Pa.

Trenton WSO CI, N.J.

Ephrata, Pa.

Neshaminy Falls, Pa.

Phoenixville IE, Pa.

Norristown, Pa.

Devault 1W, Pa.

Conshohocken, Pa.

Coatesville, 1SW, Pa.

West Chester 1W, Pa.

Moorestown, N.J.

Drexel Institute, Pa.

Pemberton 3S, N.J.

Philadelphia WSO AP, Pa.

Audubon, N.J.

Chadds Ford, Pa.

Holtwood, Pa.

Marcus Hook, Pa.

Indian Mills 2W, N.J.

Porter Reservoir, Del.

Newark, Del.

Wilmington WSO AP, Del.

Hammonton 2 NNE, N.J.

Shiloh, N.J.

Dover, Del.

Milford 2WSW, Del.

Lewes 1SW, Del.

Bridgeville 1NW, Del.

Georgetown 5SW, Del.
INTRODUCTION

! X .!

! NC'" ' 1 /

; CNENAhf<5O /

76^°__; " 0 ' ^

/ /\-5-0

*- ^-

J 5 

" DEi.AfWARE

' g _]r'' ' 'MrP-H ^.^f oo 20

25 50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 3. Numbers on the map represent locations of climatological stations. All provide Delaware River basin study precipitation data. Those numbers identified by bold print provide 

temperature data as well. Station key is on facing page.
CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN

CLIMATIC VARIABILITY

CIRCULATION OF THE MIDLATITUDES

Energy imbalances between tropical and polar regions 

exist because of variations in solar energy receipt. To 

resolve these imbalances, transfer of energy poleward 

from equatorial areas, across the middle-latitude regions, 

is necessary. It is the function of the atmospheric circulation system to achieve this transfer of energy. The 

middle-latitude regions are the zones across which the 

maximum amount of energy transfer is accomplished. 

At the surface, much of this energy transfer takes place 

at the polar front, the boundary between air masses of 

polar origin and those of the warmer, more humid 

tropics. Migrating cyclonic systems form and migrate 

along the polar front and achieve energy transfer 

through the mixing of the contrasting air masses. 

Horizontal waves in the upper level westerlies, which are 

also important for the meridional transfer of energy, are 

connected to the low-level cyclonic systems.

It is convenient to consider flow at levels above the frictional influence of the surface when examining circulation characteristics in the midlatitudes. Atmospheric 

pressure decreases with height above the surface. Upper air data are collected at numerous points above the 

Earth's surface corresponding to particular values of atmospheric pressure rather than to specific elevations 

above sea levels. Two of these levels, the 700-millibar 

level at around 10,000 ft and the 500-millibar level at 

about 18,000 ft, are frequently chosen when discussing 

upper air relations with surface weather. The actual 

height of each surface varies spatially at a given time, 

related to thermal and dynamic causes. Thus for every 

station in an upper air data network, information collected includes the elevation of each significant pressure 

surface (mean sea level) as well as temperature, humidity, and wind information.

The height at which a significant atmospheric pressure 

value occurs varies spatially, and the topography of a constant pressure surface is frequently depicted by isolines 

of constant elevation above mean sea level. On such 

maps, relatively high contour heights are associated 

with relatively high atmospheric pressure and a relatively warm atmospheric column. Relatively low contour 

heights are associated with low pressure and a relatively 

cool atmospheric column. Zones of steepest slopes on the 

constant pressure surface are zones of strongest atmospheric temperature gradient in the horizontal.

At upper levels, the forces affecting atmospheric motion are the pressure gradient force, which causes flow 

from high to low pressure areas, and the Coriolis deflection, which acts to the right of the flow in the 

Northern Hemisphere. The equilibrium flow in the upper levels, away from frictional effects of the Earth's surface, is parallel to the height contours of a constant 

pressure surface with low pressure to the left of the 

airflow path (in the Northern Hemisphere). Thus, by 

examining the topography of a constant pressure surface, 

one can determine the associated airflow pattern.

The height of the 700-millibar surface over North 

America for a typical summer day is shown in figure 4. 

The contour lines exhibit wavelike irregularities, but in 

general the 700-millibar surface slopes downward from 

south to north. The steepest slopes in the 700-millibar 

surface, associated with the steepest atmospheric 

pressure and temperature gradients, occur in the Gulf 

of Alaska and off the Newfoundland coast. These areas 

are patterned in figure 4. The steepest pressure gradients over the continent occur in southern Canada and 

are associated with the summer polar front. The arrows 

in figure 4 indicate the direction of airflow. In this situation, where the wind is flowing in an almost perfect westto-east fashion, the flow is termed "zonal."

An example that contrasts greatly with the zonal 

situation discussed above is shown in figure 5, which 

depicts a 700-millibar surface for a typical winter day. 

Here again, the highest 700-millibar surface heights are 

found in the southern areas, and the lowest heights occur in the north. A parcel of air embedded in the 

associated airflow would, in the long run, be transported 

from west to east. A well-developed wave with a "ridge" 

of relatively high pressure above western Canada and

0 400 800 MILES

0 400 800 KILOMETERS

FIGURE 4. Typical summer daily 700-millibar height contours (in 

feet) above North America. Steepest slopes in the 700-millibar 

surface associated with steepest atmospheric pressure and temperature gradients are patterned. Arrows indicate direction of 

airflow.
CLIMATIC VARIABILITY

a "trough" of relatively low pressure extending from 

Hudson Bay into the southeastern United States is 

shown in figure 5. A strong northerly component to the 

airflow is present at point A, and a strong southerly component exists at point B. This is a good example of strong 

"meridional" flow.

RELATION OF UPPER AIR FLOW TO SURFACE WEATHER

The circulation at upper levels appears to be a much 

smoothed-out version of the familiar surface weather 

map. It has considerable influence on weather conditions 

at the surface.

Temperature conditions in the atmospheric column are 

related to the height of a particular pressure surface. In 

a cold column of air, atmospheric pressure decreases 

relatively rapidly with height, and the 700-millibar 

height is relatively low. In a warm air column, the 

pressure decrease with height is less, and the 

700-millibar surface is at a relatively high altitude above 

sea level.

The polar front, the belt of strongest westerly winds, 

marks the zone of sharp contrast in air mass temperatures, separating relatively cool (or cold) air of polar 

origin from warm tropical air masses. The position of the 

polar front and the nature of the horizontal wave pat400 800 MILES

0 400 800 KILOMETERS

FIGURE 5. Typical winter daily 700-millibar height contours (in 

feet) above North America. Steepest slopes in the 700-millibar 

surface associated with steepest atmospheric pressure and 

temperature gradients are patterned. Arrows indicate direction 

of airflow. A strong northerly component to airflow is present at 

point A. A strong southerly component to airflow is present at 

point B.

tern of the upper level flow are important in determining 

temperature characteristics at the surface.

The upper level circulation also has an important affect on precipitation patterns. The contours shown in 

figure 6 represent a typical ridge-trough configuration 

in upper level airflow. Areas ahead of the trough favor 

convergence and upward motion near the surface and 

thus encourage precipitation. Migrating cyclonic systems 

tend to form in these areas and are subsequently steered 

by the general upper level flow. Areas behind the trough 

are areas of subsidence and divergence and tend to be 

regions of little precipitation.

The location of upper level troughs is very important, 

therefore, in affecting precipitation receipt. A slight 

change in the average position of a trough can result in 

serious precipitation deficits in one area and abnormally 

high precipitation totals in another. 

General Characteristics for North America. Wave trough 

and ridge axes may be located at any latitude. Typically 

three to seven waves exist around the hemisphere at one 

time. Ridges and troughs seem to have preferred locations related to mechanical and thermal influences. 

North-south-trending mountain ranges, such as the 

Rocky Mountains, cause convergence in the vertical of 

air flowing from the west to east. If constant absolute 

vorticity of the airflow is to be maintained, clockwise 

airflow should occur to the lee (east) of the barrier. This 

is a partial explanation for the frequent occurrence of 

a ridge over western North America. Thermal characteristics, such as contrast between a snow-covered land 

mass and nearby, relatively warm ocean waters, can 

often contribute to the anchoring of an atmospheric wave

FIGURE 6. Relations between the upper level airflow pattern (solid 

arrows), paths of cyclonic systems (dashed arrows), and precipitation (shaded areas). After Harman, 1971.
8 CLIMATIC ATI AS OF THE DELAWARE RIXT.R BASIN

pattern. Fixing in unusual locations results in anomalous weather associated with all parts of the wave.

During winter, circulation in North America is 

vigorous with well-defined wave patterns and sharp 

boundaries between contrasting air masses. Migrating 

storms are steered in rapid succession along tracks 

related to the prevailing upper air flow. In summer the 

circulation weakens, and the strongest westerlies occur 

at the latitude of southern Canada. Only rarely do 

vigorous cyclonic systems affect the middle latitude 

regions of the continental United States during summer.

ATMOSPHERIC CIRCULATION AND CLIMATIC VARIABILITY

On very short time scales, anomalous weather events 

may be associated with unusual upper level circulation 

features. The January 19, 1977, extreme cold weather 

along the Atlantic Coast is one such example. The upper air charts for that day (fig. 7) show extremely strong 

pressure gradients with a deep trough centered over 

Eastern Canada. This caused the rapid transport of polar 

air to the Southeastern United States. Adding to the extreme effect was the cold weather in the Midwest and 

South that had preceded this event. This upper air circulation resulted in airflow over abnormally cold land 

surfaces; snow flurries occurred in the Miami, Fla., area. 

During the same period, the Gulf of Alaska experienced 

record high temperatures because of an unusually strong 

southerly flow component (Wagner, 1977).

If unusual upper level circulation features recur or persist within a several-week period, the effect may appear 

in monthly average pressure and airflow conditions as 

well as in surface temperature and precipitation 

averages. A good example is the case of January 1978 

(see fig. 8). During this month, a persistent anomalous 

upper air flow, which featured an eastern seaboard 

trough displaced slightly west of normal, resulted in high 

precipitation totals in the Eastern United States. A 

series of cyclonic systems formed along the Gulf Coast 

and moved eastward and northward along the Atlantic 

Coast. Average monthly temperatures were far below 

normal over the United States east of the Rocky Mountains. Record or near-record precipitation totals were 

received over much of the eastern half of the country 

(Wagner, 1978).

On even longer time scales, a series of anomalous years 

can result in decadal averages significantly different 

from the norm. The three winters of 1976-77, 1977-78,

400 800 MILES

0 400 800 KILOMETERS

FIGURE 7. Shown are 500-millibar height contours (in feet) above 

North America on January 19, 1977. (From U.S. Department of 

commerce, NOAA, Daily Weather Map Series.)

and 1978-79 with accompanying record cold and 

snowfall will certainly dominate the climatic picture of 

the 1970's for most of the Eastern United States.

Evidence indicates that some individual circulation 

anomalies can be traced from season to season and 

sometimes from year to year. Several examples of selfperpetuating mechanisms operating between sea 

surface-temperature anomalies and circulation anomalies have appeared in the literature. Namias (1974) has 

suggested that the unusual weather events of the 

1972-73 water year might be related to anomalous sea 

surface temperatures in the Pacific. Namias (1966) has 

also pointed out that the 1962-65 drought that affected 

the Northeast was associated with an eastward displacement of the trough normally situated along the east 

coast. The anomalous flow component affecting the 

Northeast was from the northwest, and an unusually 

warm, dry airflow resulted. Namias suggests that a pool 

of unusually cool water off the Atlantic coast might have 

stabilized the drought pattern.

The unusually high amplitude wave over North 

America (see figs. 7 and 8), which prevailed for three 

winters (1976-77, 1977-78, and 1978-79), may have 

been related to persistent sea surface-temperature 

anomalies in the Pacific Ocean.
ATMOSPHERIC CIRCULATION AND CLIMATIC VARIABILITY

FIGURE 8. Monthly mean 700-millibar height contours (in dekameters) above the Northern Hemisphere for January 1978 

(from Wagner, 1978). Contour interval is 3 dekameters (98.4 feet). H, high; L, low.
10 CLIMATIC ATLAS OF THE DEI AWARE RIVER BASINCLIMATIC CHARACTERISTICS OF 

THE DELAWARE RIVER BASIN

The weather in the Delaware River basin is characterized by the seasonal weather changes typical of a temperate humid climate. The Atlantic Ocean to the east 

moderates temperature extremes to a certain extent, but 

this effect is not always evident because prevailing winds 

are westerly. Annual precipitation totals range from 35 

to 40 in. in the southern and western portions of the 

basin to over 50 in. in the northern areas, where terrain 

effects are apparent. Storms moving parallel to the 

Atlantic coast from the Gulf of Mexico are important 

precipitation-producing systems during the winter 

months. In summer, warm, moist air is circulated into 

the area by the Bermuda high and scattered convective 

showers contribute the bulk of the precipitation. Occasional tropical storms move into the area. The high rainfall totals associated with these systems interrupt the 

otherwise even distribution of precipitation through the 

year.

In general, cold month average temperatures are 

slightly above freezing in the southern portions of the 

basin and about 25 °F in the north. Warm month 

average temperatures range from 70 °F to almost 80 °F. 

During all times of the year, local influences can have 

profound effects on temperature. Cold air drainage, urban heat-island effects, oceanic influences, and altitude 

all play a role in determining temperature regimes 

within the basin.

TEMPERATURE

The following series of illustrations shows average 

monthly and seasonal temperature characteristics for 

the stations in the Delaware River basin counties. Accompanying each map are times series plots for four stations selected to follow a north-south transect within the 

basin.

Cooperative observers record daily maximum and 

minimum temperatures from instruments housed in 

shelters approximately 4 ft above the ground. The

average daily temperature is calculated as the average 

of the two daily extreme values. The monthly average 

temperature is the average of these daily values. In interpreting the maps and applying any of these data to 

a specific problem, allowance for local influences on 

temperature should be made. In areas of little relief and 

extensive, homogeneous land cover, the air temperature 

measured at a station may well represent a much larger 

area around the station. In areas of high relief, however, 

there may be rather great differences in thermal 

characteristics of a valley and those of adjacent ridgetops. 

Slope and exposure of a surface affect the amount of solar 

radiation absorbed and the amount of surface heating; 

great variability may exist in a small area when relief 

features are pronounced, as in the northern portions of 

the Delaware River basin (see fig. 9). In general, 

temperature decreases with altitude. However, under certain weather conditions accompanied by clear skies and 

calm winds, cool air tends to flow toward low spots in 

the terrain. Then temperature inversion conditions exist and valleys are actually cooler than adjacent ridges. 

If sufficient moisture is present in the atmosphere, fog 

may form in the cooler air of lower elevations.

The land cover and land use around a station also influence the representativity of temperature measurements taken. Local surface characteristics such as reflectivity of incoming solar radiation (albedo), thermal 

conductivity and heat capacity of the surface materials, 

and moisture characteristics determine the amount of 

incoming solar radiational energy that ultimately is 

used to heat the atmosphere above the surface. A great 

contrast in these parameters exists between typical urban surfaces and vegetated rural surfaces. Differences 

in surface characteristics and building geometry along 

with emission of waste heat by industry and by domestic 

heating result in urban temperatures being higher, on 

the average, than temperatures recorded in the surrounding rural countryside. In the Delaware River basin, 

the urban influence on temperature is dramatically illustrated in the Philadelphia, Pa., area.
CLIMATIC CHARACTERISTICS OF THE DELAWARE RIVER BASIN 11

FIGURE 9. The rugged terrain of the Catskill Mountains in the New York portion of the Delaware River basin leads to great 

variability in temperature and precipitation characteristics over small areas.
12 CLIMATIC ATLAS OF THE DEI AWARE RIVER BASIN

AVERAGE ANNUAL TEMPERATURE

The influences of latitude, station elevation, and urbanization affect the distribution of annual average 

temperature within the Delaware River basin (figs. 10 

and 11). A systematic latitudinal decrease in 

temperature in the southern portion of the basin is interrupted by the urban heat-island effect in the 

Philadelphia area. In the northern half of the basin, 

significant terrain effects result in relatively low average 

annual temperatures in the high elevations of the 

Poconos and the Catskills. The Delaware stations 

generally have average temperatures in the 54-55 °F 

range, and the stations in the northern portion of the 

basin show averages in the 44-46 °F range. Dover, Del., 

has the highest average annual temperature of 56.2 °F; 

Pleasant Mount, Pa., has the lowest average annual 

temperature of 42.9 °F. Time series plots (fig. 10) of the 

annual values for the four representative stations show 

the year-to-year variability in this parameter.

HAWLEY, PA.

MAXIMUM 48.3° F

MINIMUM 43.9° F

MEDIAN 4S.7°F

MEAN 4S.7°F

'STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

68 70 72 74 76 78

60

2 50

BELVIDERE, N.J.

MAXIMUM 54.1° F 

MINIMUM 47.9°F 

MEDIAN S0.1°F 

MEAN 50.5°F 

STANDARD DEVIATION 1.73°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

60

2 50

40

GEORGETOWN, DEL.

MAXIMUM 57.5°F 

MINIMUM 53.4°F 

MEDIAN 55.2° F 

MEAN 55.3° F 

STANDARD DEVIATION 1.09°F

50 52 54 56 58 60 62 64 66 68 70 72 

YEARS

74 76 78

60

2 50

40

INDIAN MILLS..N.J.

MAXIMUM S1.0°F 

MINIMUM S4.7°F 

MEDIAN S2.8°F 

MEAN S2.8°F 

STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 

YEARS

70 72 74 76 78

FIGURE 10. Average annual temperature at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 13

Temperature, in degrees 

' x - ' /« ~c£ \ Fahrenheit

~r""r~* »EN\ J-^-^d^ 8&&. ) J_A r

^Jejf^O ^

A'ientowiVX ^ \ ../ \ ^r~ C 

. V .-*>-.- ^.#* ....j.^^i. ^«. >

feS^^' I ^ , \

. ape May

\

|M en lopen

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP. 1970

' R" f^ FIGURE 11. Distribution of average annual temperature in the

Delaware River basin.
14 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

AVERAGE DECEMBER TEMPERATURE

Average temperatures during December range from 

over 38 °F in the south to 24 °F at Pleasant Mount, Pa., 

in the north (figs. 12 and 13).

The time series plots (fig. 12) indicate a return to the 

high degree of year-to-year variability associated with 

the winter months.

50

30

2 20

a

HAWLEY, PA.

MAXIMUM 32.7°F

MINIMUM 19.7°F

MEDIAN 28.2°F

MEAN 27.4°F

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

76 78

40

2: 30

20

10

BELVIDERE, N.J.

MAXIMUM 37.3'

MINIMUM 24.0'

MEDIAN 32.2'

MEAN 31.3'

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

76 78

2: so

20

GEORGETOWN, DEL.

MAXIMUM 46.4° F 

MINIMUM 294°F 

MEDIAN 38.2°F 

MEAN 37.8° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 

YEARS

74 76 78

30

20zu

10

INDIAN MILLS, N.J.

MAXIMUM 41.1°F 

MINIMUM 27.2°F 

MEDIAN 35.6°F 

MEAN 34.8°F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGURE 12. Average December temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 15

76° | ' \

r -^rr -d

Temperature, in degrees 

Fahrenheit

EXPLANATION

50 MILES

50 KILOMETERS

BASE FROM U.S GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

Gisef|

S S C^-^v^? - * FIGURE 13. Distribution of average December temperatures in the

Delaware River basin.

-sa
16 CLIMATIC ATLAS OF THE DEI AWARE RIVER BASIN

50

AVERAGE JANUARY TEMPERATURE

January mean temperature conditions are plotted and 

mapped in figures 14 and 15. A steep south-to-north 

temperature gradient in January mean temperature is 

shown in the contour map (fig. 15). Stations in the 

southern part of the basin average 35-36 °F, and the 

northern stations average less than 22 °F. The heatisland effect of the Philadelphia urban area is again evident. In addition, temperature patterns in the northern 

half of the basin are significantly affected by the high 

elevations of the Catskills and the Poconos.

Time series plots of the annual values (fig. 14) provide 

a graphical impression of the year-to-year variability in 

January mean temperature. Especially noteworthy in 

these series are the very high average temperatures experienced at all locations in the early 1950's and the 

record low values of January 1977.

HAWLEY. PA.

MAXIMUM 33.1 °F 

MINIMUM 13.2°F 

MEDIAN 23.2° F 

MEAN 22.7° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 

YEARS

72 74 76 78

BELVIDERE, NJ.

50

2 20 

Q

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50

2 30

20

GEORGETOWN, DEL.

MAXIMUM 48.7° F

MINIMUM

MEDIAN

ulEAN

STANDARD

50 52 54 56 58 60 62 64 66 68 70 72 

YEARS

74 76 78

2 30

10

INDIAN MILLS, N.J.

MAXIMUM 43.2° F 

MINIMUM 21.1°F 

MEDIAN 30.8°F 

MEAN 31.3" F 

/STANDARD DEVIATION 444°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGLRE 14. Average January temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 17

fe* fe F£ 0 0 N 

I i ' U' -.i*^f\'3>\>

42

EXPLANATION

Temperature, in degrees 

Fahrenheit

34.0

32.0

30.0

28.0

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

^*T> ; , ^_ v *" rf FIGURE 15. Distribution of average January temperatures in the

Delaware River basin.
18 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE FEBRUARY TEMPERATURE

The month of February shows the greatest range in 

average temperatures throughout the basin (figs. 16 and 

17). Southern Delaware stations average 35-37 °F, and 

the northern stations show average temperature less 

than 22 °F. The urban influence at Philadelphia is 

marked.

Annual time series plots (see fig. 16) show a series of 

warm Februaries in the early 1950's and particularly 

cold temperatures in 1978 and 1979.

40

£ 30

20

10

HAWLEY, PA.

MAXIMUM 30.7°F

MINIMUM 14.9°F

MEDIAN 24.0°F

MEAN 23.6° F

'STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50

40

30

70^u

BELVIDERE, N.J.

MAXIMUM 38.0°F

MINIMUM 20.1° F

MEDIAN 29.0° F

MEAN 29.4°F

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

30

GEORGETOWN, DEL.

MAXIMUM 43.0° F 

MINIMUM 24.3°F 

MEDIAN 36.0° F 

MEAN 36.0° F 

STANDARD DEVIATION 4 38°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50

40

£ 30

10 U

INDIAN MILLS, N.J.

MAXIMUM 41.1°F 

MINIMUM 22.6° F 

MEDIAN 33.2°F 

MEAN 32.8° F 

/STANDARD DEVIATION 422°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 16. Average February temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 19

>"** . V *»,¥ - * . "1 >vn.-.'-v ls W f^\"f ! 

/' ^C^ /* ' \^*& )*»&<& - A

/ t^/. ^^ l> ^sfeZ^S

' ,-'- i- *v / -^-" ^O^" i X ^

/\ Mjrr^kjw *» * ». ww^«- V

EXPLANATION

Temperature, in degrees 

Fahrenheit

50 MILES 

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 17. Distribution of average February temperatures in the 

Delaware River basin.
20 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

AVERAGE MARCH TEMPERATURE

The range in average temperature over the Delaware 

River basin in March is from values below 32 °F in the 

northern counties to values in the 42-44 °F range in the 

south (figs. 18 and 19). The lowest average March 

temperature is 29.0 °F at Pleasant Mount, Pa.; the 

highest average temperatures of 44.2 °F are at Milford 

and Dover, Del.

Time series plots are shown in figure 18. The month 

of March 1960 was particularly cool at all four of the 

transect stations as well as over most of the United 

States east of the Rockies. This was a result of the 

development and persistence of a particularly deep 

trough along the East Coast. An unusually strong 

northerly flow was associated with this trough and the 

entire Eastern United States was dominated by a persistently cold air mass (Dunn, 1960).

HAWLEY, PA.

MAXIMUM 39.5° F 

MINIMUM 22.8°F 

MEDIAN 32.1° F 

MEAN 32 4° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 

YEARS

72 74 76 78

50 r

tr 40

30

20

BELVIDERE, N.J.

MAXIMUM 44.1° F 

MINIMUM 30.3° F 

MEDIAN 38.6° F 

MEAN 38.5° F 

/STANDARD DEVIATION 310°F

50 52 54 56 58 60 62 64 66 68 70 

YEARS

72 74 76 78

cc 40

CO

UJ 30 

cc

O

LU

Q 

20

GEORGETOWN, DEL.

MAXIMUM 48.5° F 

MINIMUM 32.8° F 

MEDIAN 43 6° F 

MEAN 43.5° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

INDIAN MILLS, N.J.

MAXIMUM 46.9° F 

MINIMUM 31.8°F 

MEDIAN 40.6° F 

MEAN 40.7° F 

STANDARD DEVIATION 3.17°F

50 76 78

FIGURE 18. Average March temperature at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 21

EXPLANATION

Temperature, in degrees

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

!' ] '. FIGURE 19. Distribution of average March temperatures in the

Delaware River basin.
22 ATLAS OF THE DEI AWARE RIVER BASIN

AVERAGE APRTL TEMPERATURE

As the hemispheric temperature gradient weakens, so 

does the contrast in temperatures along the north-south 

axis of the Delaware River basin. April average temperatures range from greater than 54 °F in the south to less 

than 44 °F in the northern areas (figs. 20 and 21). Urban effects are evident in the Philadelphia area.

Time series plots for April are shown in figure 20.

60 r

HAWLEY, PA.

MAXIMUM 49.7°F 

MINIMUM 39.5°F 

MEDIAN 44 8° F 

MEAN 44 5° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 68 70 72 74 76 78

YEARS

30

BELVIDERE, N.J.

MAXIMUM 549'

MINIMUM 441'

MEDIAN 49.7'

MEAN 49.5

STANDARD DEVIA

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

GEORGETOWN, DEL.

60

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

60

50

INDIAN MILLS, N.J.

MAXIMUM 55.7°F

MINIMUM 461°F

MEDIAN 51.2°F

MEAN 51 0°F

'STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 20. Average April temperatures at four stations in the Delaware River basin, 1950-79.
42

F ^^JSe

X" PENJ)iS¥LVAN>)\

\ ?<*> S*

\ ^ ^ ,., L^'

>Ef^wAKFmm^,.^

EXPLAIN! ATIOIM

Temperature, in degrees 

Fahrenheit

' J

>

54.0 

52.0 

50.0 

48.0 

46.0 

44.0

0 25

I I . , , I

50 MILES

I

25 50 KILOMETERS

'^^^^y^- ^ \ ' - » FIGURE 21. Distribution of average April temperatures in the

BASE FROM U.S. GEOLOGICAL SURVEY ^ - -- *V " UNITED STATES BASE MAP, 1970 LIR*

Delaware fVlawarp Kiver River basin Dasm.
24 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE MAY TEMPERATURE

May average temperatures range from less than 

54 °F to over 62 °F depending on latitude (figs. 22 and 

23). The Philadelphia urban heat-island effect is 

apparent.

Particularly low May average temperatures occurred 

at all stations in 1967. An unusually deep trough was 

situated along the eastern seaboard during the first half 

of that month. Associated with it was a strong northerly 

flow component that resulted in relatively cool temperatures along the east coast. Trenton, N.J., in the 

Delaware basin, experienced the coldest May since 1917 

(Stark, 1967).

Time series plots for May are shown in figure 22.

HAWLEY, PA.

MAXIMUM 59.5° F

MINIMUM 47.7° F

MEDIAN 54.6° F

MEAN 54.4° F

''STANDARD DEVIATION 295°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

70

BELVIDERE, N.J.

MAXIMUM 65.0° F 

MINIMUM 52.4° F 

MEDIAN 59.4° F 

MEAN 59.4° F 

STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

76 78

GEORGETOWN, DEL.

MAXIMUM 68.4'F 

MINIMUM 57.8° F 

MEDIAN 62.3° F 

MEAN 63.0° F 

/STANDARD DEVIATION 247°F

INDIAN MILLS, N.J.

MAXIMUM 652°F 

MINIMUM 54.2°F 

MEDIAN 604°F 

MEAN 60.8° F 

STANDARD DEVIATION 2.51° F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

FIGURE 22. Average May temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE

Temperature, in degrees 

Fahrenheit

EXPLANATION

40 ° .^,- ' ' '

"i f;4T ,mru .

50 MILES

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 23. Distribution of average May temperatures in the 

Delaware River basin.
26 CLIMATIC ATIAS OF THE DEI AWARE RIVER BASIN

AVERAGE JUNE TEMPERATURE

In June, average temperatures in the Delaware River 

basin range from less than 63 °F to over 72 °F. (figs. 24 

and 25).

Time series plots (fig. 24) indicate low year-to-year 

variability during the 1960's at the two stations in the 

southern part of the basin, Georgetown, Del., and Indian 

Mills, N.J.

HAWLEY, PA.

MAXIMUM 666°F 

MINIMUM 59.4°F 

MEDIAN 636°F 

MEAN 63.2°F 

/STANDARD DEVIATION

70

60

BELVIDERE, N.J.

MAXIMUM 74 3° F 

MINIMUM 640°F 

MEDIAN 68.2°F 

MEAN 67.9° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 6 

YEARS

68 70 72 74 76 78

50

GEORGETOWN, DEL.

MAXIMUM 75.6°F 

MINIMUM 67.6°F 

MEDIAN 71.8°F 

MEAN 71.5°F 

STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

60

50

INDIAN MILLS, N.J.

MAXIMUM 72.9° F

MINIMUM 667°F

MEDIAN 69.4° F

MEAN 69.6° F

STANDARD DEVIATION 1 60°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 24. Average June temperature at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 27

*** \t,l,K#fot/-,'-h ~Ji , , A.., _ j f

" »P^ !^S<<P4«'*'S 'X^/''

} **><£*'/ 

^ ^r'/x/ strssexy*" ^ 

: >«*I.M - r 

\ _ /'C-% ,V.. ./-V .^,-isEXPLANATION

Temperature, in degrees 

Fahrenheit

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY p '^J*^- 

UNITED STATES BASE MAP, 1970 jj

FIGURE 25. Distribution of average June temperatures in the 

Delaware River basin.
28 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

AVERAGE JULY TEMPERATURE

July is the month associated with the mildest 

latitudinal temperature gradient over the Northern 

Hemisphere and within the Delaware River basin 

(figs. 26 and 27). The highest average temperature is 77.7 

°F at Marcus Hook, Pa., a station within the 

Philadelphia metropolitan area; coolest average temperatures occurred at Pleasant Mount, Pa., with a mean 

July temperature for the 30-year period of 65.1 °F.

Time series plots (fig. 26) indicate low year-to-year 

variability when compared with those of winter months.

90

80 -

HAWLEY, PA.

MAXIMUM 70.2°F 

MINIMUM 63.9°F 

MEDIAN 680°F 

MEAN 67.5°F 

^STANDARD DEVIATION

52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

b 90 r

LU I

BELVIDERE, N.J.

MAXIMUM 80.2°F

MINIMUM 68.4°F

MEDIAN 71.6°F

MEAN 72.2°F

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

90

60

GEORGETOWN, DEL.

80.6°F 

73 7° F 

75.8°F

MAXIMUM 

MINIMUM 

MEDIAN

MEAN 76.0°F

'STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

68 70 72 74 76 78

INDIAN MILLS, N.J.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 26. Average July temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE

EXPLANATION

Temperature, in degrees 

Fahrenheit

76.0

74.0

72.0

70.0

68.0

66.0

25 50 MILES

I 

25

\ 

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

. " i ' - ' FIGURE 27. Distribution of average July temperatures in the

Delaware River basin.

sk _«£i1
3 

c gN3

00

i

o^ 

re

Crq

re

3t3 

rc3 

§!/)

PI

P!/)3'

? re

Ore1

re cr3' i '

CD On

I

S - >D S X

05 2 ^ ^ C^ & T ^ ^ > ±p CB "-s H 03 ^ £i crq c o jr- &^ °S ?> P £ 5

SiFgSSjj

co ?_ ^ o > 

^

^ of 3 ^cg ?r

IT) u~. K' P <^~ PS 3 to p g. » Hi g CO r* g >

II' =11 I

jo 05 O fO 2" W ^ co 3. crq g >

&U ? * 3 o

<-> ^~~- ^n P3 H

3 <P ^ § »' 1 2 to ^ g. § S <^ r*^ i r* r+ > ^ LAJ -^.J p ^3 ^ ^ S o 5

oq P o co "> w

^ tj ^^ ^ ^^H o CB 

^

c? § 

^ >CS 

^

crq 1-5 e^, o

co »-- 0) o P rt- P B " ^ f S 3 B"ll |S § V «< S^ CO CO

DEGREES FAHRENHEIT 

§ ^_

ui - ~
TEMPERATl'RE 31

Temperature, in degrees 

Fahrenheit

 >gftis«tan r jfr**

EXPLANATION

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 29. Distribution of average August temperatures in the 

Delaware River basin.
CLIMATIC ATLAS OF THE DEIAWARE RIVER BASIN

HAWLEY, PA.

AVERAGE SEPTEMBER TEMPERATURE

Pleasant Mount, Pa., has the lowest average 

September temperature in the basin at 56.4 °E Highest 

averages are shared by Dover, Del., and Drexel Institute 

in Philadelphia at slightly over 69 °F 

(figs. 30 and 31). The Philadelphia heat island is apparent on the September average temperature map.

Time series plots for September are shown in 

figure 30.

80

50

BELVIDERE, N.J.

MAXIMUM 69.8°

MINIMUM 58.2°

MEDIAN 64.01

MEAN 63.7'

'STANDARD DEVIA 2.64° F

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

70

60

GEORGETOWN, DEL.

MAXIMUM 73.1° F

MINIMUM 64.8°F

MEDIAN 67 8° F

MEAN 68 2° F

'STANDARD DEVIATION 202°F

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

80

INDIAN MILLS, N.J.

MAXIMUM 71.2°F 

MINIMUM 61.5°F 

MEDIAN 65.8°F 

MEAN 65.8° F 

'STANDARD DEVIATION

50 52 62 64 66 

YEARS

70 72 74 76 78

FIGURE 30. Average September temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE

74 C

^T*

r-t

y, <!_< 

v " Schrr'var J^ ~ j

\' ^ y * \ ' "~-V \>^rif 

T^J)

Cat^!»^f

Sf+Sij' N , 

__ ^

 ^' ^.V,\',^.' ./»-," **>'

%: J^gr^c -^^

Temperature, in degrees 

Fahrenheit

"'^XA-^Sskj^T^gU;

50 MILES

J

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY f 

UNITED STATES BASE MAP, 1970

r ^ ,'*"' s" ! ' *" FIGURE 31. Distribution of average September temperatures in the Delaware River basin.
CLIMATIC AT1AS OF THE DELAWARE RIVER BASIN

t 70 r

in )

AVERAGE OCTOBER TEMPERATURE

October average temperatures range from over 58 °F 

at Dover, Del., and at Drexel Institute to 43.3 °F at Pleasant Mount, Pa., in the north (figs. 32 and 33). The urban effect of Philadelphia is apparent.

Time series plots for October are shown in figure 32.

HAWLEY. PA.

MAXIMUM 54 6°F 

MINIMUM 43.0°F 

MEDIAN 48.6°F 

MEAN 49.0°F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

BELVIDERE, NJ.

MAXIMUM 58.5°F 

MINIMUM 47.5°F 

MEDIAN 54.0°F 

MEAN 53.2°F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

GEORGETOWN, DEL.

MAXIMUM 63.0°F 

MINIMUM 51.8°F 

MEDIAN 57.8° F 

MEAN 57.2°F 

STANDARD DEVIATION

70

LU 50 

o

40

INDIAN MILLS, N.J.

MAXIMUM 61.6°F

MINIMUM 506°F

MEDIAN 54.7°F

MEAN 55.0° F

/STANDARD DEVIATION 2.78

50 52 54 56 58 60 62 64 66 

YEARS

68 70 72 74 76 78 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 32. Average October temperatures at four stations in the Delaware River basin, 1950-79.
c ,- 

. V. _. -

760 i '\> rv'-fj^-T^ i

\ \ *fP

« i -W S C ' H'r-----i

Temperature, in degrees 

Fahrenheit

\XJS*a*tf ^^y?^,

»l!., .K-^S^^^

50 MILES 

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 1 

UNITED STATES BASE MAP, 1970

* FIGURE 33. Distribution of average October temperatures 

in the Delaware River basin.
36 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN

AVERAGE NOVEMBER TEMPERATURE

Average temperatures in November range from 46-48 

°F in the south to 36-38 °F in the north (figs. 34 and 35).

The month of November 1976 averaged well below the 

1950-79 mean November temperature value at all stations. As in situations previously described, this was 

related to an unusually deep East Coast trough that 

resulted in advection of cold air from high latitudes into 

the Eastern United States (Dickson, 1977).

Time series plots for November are shown in figure 34.

50

LIJ 40

HAWLEY, PA.

MAXIMUM 44.1°F 

MINIMUM 32.3°F 

MEDIAN 39.4°F 

MEAN 38.9 °F 

/STANDARD DEVIATION

50 52 54 56 58 60

30

62 64 66 68 70 72 74 

YEARS

76 78

BELVIDERE, N.J.

MAXIMUM 48.0° F

MINIMUM 36.9° F

MEDIAN 42.8°F

MEAN 42.4° F

STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50

40

30

GEORGETOWN, DEL.

MAXIMUM 51.5°F

MINIMUM 39.9° F

MEDIAN 47.7°F

MEAN 47.3°F

/STANDARD DEVIATION 2.54°F

,1^ -^r^^\ r^

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

j_ 60

LIJ

I

z

LIJ

I 50 

u_

LULIJ 40

LIJ

Q 

30

INDIAN MILLS, N.J.

MAXIMUM 50.3° F

MINIMUM 39.2°F

MEDIAN 45.4°F

MEAN 45 0°F

/STANDARD DEVIATION 2 60°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 34. Average November temperatures at four stations in the Delaware River basin, f 950-79.
TEMPERATURE 37

P j \ ~ », *> ' ^TAWA

B&

EXPLANATION

Temperature, in degrees 

Fahrenheit

TJ1> ^Sandy 

 V ">^00k

46.0 

44.0 

42.0 

40.0 

38.0

25

, I

50 MILES 

I

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

-iJl'v- '. FIGURE 35. Distribution of average November temperatures in the Delaware River basin.
CLIMATIC: ATLAS OF THE DELAWARE RIVER BASIN

AVERAGE WINTER TEMPERATURE

Average temperatures for the winter season are plotted 

and mapped in figures 36 and 37. The map of average 

December-February temperatures is a composite of the 

individual monthly maps (fig. 37). In the southern half 

of the basin, the latitudinal decrease in average 

temperature is evident as is the Philadelphia urban 

heat-island effect. In the northern part of the basin, 

elevation differences and alignment of topographic 

features combine with the effects of distance from 

continental and oceanic influences to produce a 

temperature-distribution pattern skewed to that of the 

southern half of the basin. Average temperatures for 

winter range from values of 22 to 24 °F in the northern 

sector to over 36 °F in the southern portions of the basin.

Because of the steep hemispheric temperature gradient that develops during winter, slight shifts in the 

midlatitude circulation features from one year to the 

next may result in significant departures from expected 

temperature values for midlatitude locations. Thus, the 

time series graphs (fig. 36) for winter temperatures in 

the Delaware River basin indicate considerable year-toyear variability. A slight decrease in average winter 

temperature is evident at all four transect stations 

during the 1950's and 1960's. The winters of 1971-72 

through 1975-76 were relatively warm. The cold 

temperature conditions of the following three winters 

(1976-77 through 1978-79) are reflected in the graphs.

40

HAWLEY, PA.

MAXIMUM 29.1° F 

MINIMUM 19.3° F 

MEDIAN 24.6° F 

MEAN 24.4° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

BELVIDERE, NJ.

MAXIMUM 34.8° F 

MINIMUM 24.0° F 

MEDIAN 28.7°F 

MEAN 29.3° F 

/STANDARD DEVIATION

60 62 64 66 

YEARS

30

20

GEORGETOWN, DEL.

MAXIMUM 40.1° F

MINIMUM 30.1° F

MEDIAN 35.8° F

MEAN 35.9° F

/STANDARD DEVIATION 2.88° F

50 52 54 56 58 60 62 64 66 68 70 

YEARS

72 74 76 78

45

INDIAN MILLS, N.J.

MAXIMUM 372°F 

MINIMUM 2B.3°F 

MEDIAN 32.4° F 

MEAN 32 8° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 

YEARS

70 72 74 76 78

FIGURE 36. Average winter (December-February) temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATl'RE 39

Temperature, in degrees 

Fahrenheit

50 MILES

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 37. Areal distribution of average winter (December-February) temperatures in the Delaware River basin.
40 CLIMATIC ATIAS OF THE DEIAWARE RIVER BASIN

AVERAGE SPRING TEMPERATURE

Average spring (March-May) temperatures range from 

over 54 °F to less than 42 °F (figs. 38 and 39). The 

Philadelphia area exhibits average temperatures of up 

to 2 °F warmer than outlying areas at the same latitude.

Less year-to-year variability exists in average spring 

temperature than in average temperature for the winter 

months. No year or period of years stands out as an extreme case.

The spring of 1977 was significantly warmer than the 

30-year average. This was a result of a weakening of the 

normally occurring East-Coast trough. A ridge existed 

over the East Coast and brought in warm air from the 

south (Taubensee, 1977). The trough was present along 

the coast during the following April but was weak in the 

latitude of the Delaware River basin (Wagner, 1977b).

9= 50

HAWLEY, PA.

MAXIMUM 46.9°F 

MINIMUM 39.7°F 

MEDIAN 43.8°F 

MEAN 43.9° F 

/STANDARD DEVIATION

54 56 58 60 62 64 66 68 70 72 74 

YEARS

60

LLJ 45

cc 

O

BELVIDERE, N.J.

MAXIMUM 53.6°F 

MINIMUM 45.1 °F 

MEDIAN 48.9°F 

MEAN 49.2°F 

' STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

68 70 72 74 76 78

C/3

LU 45

EC

o

LU

Q 

40

35

GEORGETOWN, DEL.

MAXIMUM 56.2°F 

MINIMUM 50.3°F 

MEDIAN 53.3° F 

MEAN 53.3° F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

EC 50

Lu 45

oc

o

35

INDIAN MILLS, N.J.

MAXIMUM 54.8°F

MINIMUM 47.6°F

MEDIAN 50.9° F

MEAN 50.9°F

'STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 38. Average spring (March-May) temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 41

7

EXPLANATION

Temperature, in degrees 

Fahrenheit

54.0

52.0

50.0

48.0

46.0

44.0

42.0

25 50 MILES 

I

25 50 KILOMETERS

i^1

'0 |j *ji f^.:^* v '; ''' ' f '' Fica'RE 39. Area\ distribution of average spring (MarchMay)
CLIMATIC ATIAS OF THE DELAWARE RIVER BASIN

80

AVERAGE SUMMER TEMPERATURE

Average summer (June-August) temperatures range 

from less than 64 °F in the northern part of the basin 

to over 74 °F in central and southern Delaware and in 

the Philadelphia area (figs. 40 and 41).

Summer is the season of minimal contrasts in temperature between high and low latitudes; therefore, little 

chance exists for extremes of temperature to occur 

during a particular year.

HAWLEY, PA.

MAXIMUM 68.5°F 

MINIMUM 63.0°F 

MEDIAN 65.6° F 

ulEAN 65.6°F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

I 75

70

60

BELVIDERE, N.J.

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

GEORGETOWN, DEL.

MAXIMUM 75.9°F

MINIMUM 71.7°F

MEDIAN 74.2°F

MEAN 74.1 °F

'STANDARD DEVIATION

50 52 54 56 60 62 64 66 68 70 72 

YEARS

74 76 78

INDIAN MILLS, N.J.

I 75

70

60

MAXIMUM 

MINIMUM 

MEDIAN 

MEAN

74.8" F 

70.4°F 

72.0°F 

72.2°F

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 40. Average summer (June-August) temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 43

, ,.-»wHs-Trvffffk~ &!& ' IS

/-" 

EXPLAIN! ATIOIM

Temperature, in degrees 

Fahrenheit

74.0

72.0

70.0

68.0

66.0

64.0

25 50 MILES

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGIJRE 41. ^Areal distribution of average summer (JuneAugust) temperatures in the Delaware River basin.
44 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN

AVERAGE FAEE TEMPERATURE

Fall (September-November) average temperatures 

range from less than 48 °F in the north to over 58 °F 

in Delaware (figs. 42 and 43). The Philadelphia area 

stands out as being relatively warm for the latitude.

60

55

50

HAWLEY, PA.

MAXIMUM 53.6°F 

MINIMUM 45.5°F 

MEDIAN 486°F 

MEAN 48.9 °F 

/STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

65

I 60

45

BELVIDERE, NJ.

MAXIMUM 56.8°F

MINIMUM

MEDIAN

MEAN

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

60

2 55

50

GEORGETOWN, DEL

MAXIMUM 60.2° F 

MINIMUM 52.5°F 

MEDIAN 58.0°F 

MEAN 57.6°F 

STANDARD DEVIATION

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

65

60

55

45

INDIAN MILLS, N.J.

MAXIMUM 58.2° F

MINIMUM 51.5°F

MEDIAN 55.4° F

MEAN 55.3° F

'STANDARD DEVIATION i.73°F

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGLRE 42. Average fall (September-November) temperatures at four stations in the Delaware River basin, 1950-79.
TEMPERATURE 45

Temperature, in degrees 

Fahrenheit

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY |

UNITED STATES BASE MAP, 1970 ^

' '' FIGURE 43. Areal distribution of average fall (SeptemberNovember) temperatures in the Delaware River basin.
46 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN-

? v- ' V '

' .,* - t

Btnghamton **** -- ._ - 

AHentown

. Witrriington

0 25 50 MILES 

 

0 25 50 KILOMETERS

1 V---

,,. X

TEMPERATURE EXTREMES

Knowledge of typical diurnal variation in temperature 

for a month is sometimes more useful than a single 

monthly average temperature. Graphs of monthly 

averaged daily maximum and minimum temperature for 

three first-order stations are shown in figure 44. Average 

diurnal temperature range at all stations is slightly 

greater during the summer months than during the 

winter months, a result of greater average cloudiness in 

winter.

BINGHAMTON, N.Y.

110

100

90

80

70

H

I 60

z

LU

^ 50 

<

LL

w 40

LU 

LU

5 30

LU

Q

20

10 

0

-10 

20

\\

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

BASE FROM U.S. GEOLOGICAL SURVEY

UNITED STATES BASE MAP, 1970 ' u '

WILMINGTON,DEL ALLENTOWN.PA.

110

100

90

80

70

60

50

40

30

20

10

0

-10

-20

\\ \ i i i i r

i i i i i i i I I

110 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

10 

-20

I I I

JAN FEB MAR APR MAY JUNE JULY AUG SEPT DCT NOV DEC

i i i i i i i i i i I

JAN FEB MAR APR MAY JUNE JULY AUG SEPT DCT NDV DEC

FIGURE 44. Monthly averaged daily minimum and maximum temperatures at 

three stations in the Delaware River basin, 1950-79.
TEMPERATURE 47

Daytime cloud cover diminishes incoming radiational 

energy; the result is a lower daily maximum temperature than under clear sky conditions. A cloud cover 

very effectively absorbs and reradiates terrestrial radiation and thereby "traps" energy in the lower atmosphere 

(fig. 45). Daily minimum temperatures therefore tend to 

be higher under cloud cover than under clear sky conditions.

Figure 44 also shows the absolute extreme daily maximum and minimum temperatures, that is, the highest 

and lowest temperatures recorded during a given month 

for the 1950-79 period. The greatest range between maximum and minimum values is associated with the winter 

months. These extreme temperature measurements 

represent short term, rather than persistent, conditions. 

The winter months, with great contrasts in temperature 

north and south of the basin, are associated with a 

higher probability of extreme temperature occurrences 

in either direction.

The graphs in figure 46 show the yearly time series 

of average daily maximum and minimum temperatures 

for the months of January and July for the years 

1950-79.

BINGHAMTON, N.Y.

 

1 T

[

Less than 1 day per month

20 -

J_I I 1

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

ALLENTOWN,PA. 

10 i 

WILMINGTON,DEL.

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

EXPLANATION

Average number of 

days per month with 

maximum temperature 

90 °F or above

Average number of 

days per month with 

minimum temperature 

32 °F or below

FIGURE 45. Average frequency of days per month of temperatures equal to or above 90 °F and equal to or below 32 °F at

three stations in the Delaware River basin.
48 CLIMATIC ATLAS OF THE DEI AWARE RATR BASIN

The frequency with which a particular threshold value 

of temperature is exceeded is important for many 

climatic applications. The critical threshold may be 

related to the planning of outdoor work such as construction, to the design of a building heating or cooling 

system, or to the scheduling of agricultural activities. 

Because each application is associated with a different 

set of critical temperatures, it is not practical to include 

all possibilities here.

Graphs indicating the average frequency of days per 

year with temperature equal to or exceeding 90 °F and

Average Daily Maximum and Minimum Temperature -January

BINGHAMTON, N.Y.

20

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

the frequency of days with minimum temperatures of 32 

°F or below are shown in figure 47. The latitudinal trend 

is obvious. Wilmington, Del., averages 18 days of temperatures 90 °F or above per year; Allentown, Pa., averages 

14 days; and Binghamton, N.Y., averages 2 days. A 

systematic trend also appears in the frequency of days 

with subfreezing temperature. For example, the average 

number of days with minimum temperature of 32 °F or 

below is 102 for Wilmington, Del., 125 for Allentown, 

Pa., and 147 for Binghamton, N.Y. (fig 47).

Average Daily Maximum and Minimum Temperature -July

BINGHAMTON, N.Y.

IS 70

LU

cc 

e>

LU

0 60

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

ALLENTOWN,PA.

40

30

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

,_ ALLENTOWN.PA.

Minimum

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

WILMINGTON,DEL. 50

40

20

10

0 U i i I i i i i i i i i i i i i i i i i i i i i i i i i i i

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

YEARS

WILMINGTON.DEL

80

50 U

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 46. Average daily maximum and minimum temperatures for January and July, 1950-79, at three stations in the Delaware

River basin.
TEMPERATURE 49

Number of Days with Maximum Temperature 90 °F or above

60 r BINGHAMTON, N.Y.

50

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

Number of Days with Minimum Temperature 32 °F or below

180 r BINGHAMTON, N.Y.

120

60

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

60

50

40

CO 

> 30

Q

20

10 

n

-

-

-

-

ALLENTOWN,PA.

-

r-

-

-

r-i r-

-

rn

~ ~

TJ

, I

-

-

-

180

150

120 

CO

<t 90

Q

60

30 

n

ALLENTOWN,PA.

-

-

-

rn

 I

pn

-

-

-|

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

50

40

< 30

Q

WILMINGTON.DEL.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

120

CO

>. 90

WILMINGTON.DEL.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 47. Average frequency of days per year of temperatures equal to or above 90 °F and equal to or below 32 °F at three

stations in the Delaware River basin, 1950-79.
50 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

HEATING DEGREE DAYS

The heating degree-day statistic was developed for use 

by the heating industry, and it relates outdoor air 

temperature to fuel consumption for heating purposes 

(figs. 48 and 49). A temperature of 65 °F is commonly 

used as a base value. Presumably, no heating is 

necessary when the average daily temperature is greater 

than 65 °F. Heating degree days for a day during which 

the average temperature is less than 65 °F are calculated 

by subtracting that average temperature from the base 

value. The heating degree-day total for the day with an 

average temperature of 45 °F would be 20.

The graphs on figure 49 show the average monthly 

distributions of heating degree days for the three firstorder transect stations. Annual average heating degreeday totals for the 1951-79 heating seasons are 4,991, 

5,756, and 7,329 for Wilmington, Del., Allentown, Pa., 

and Binghamton, N.Y., respectively.

Time series plots of the annual total heating degree 

days for the same three stations are shown in figure 48.

LJJ

5000 d

LJJ

Q 

d 

? 4000

BINGHAMTON, N.Y.

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

76 78

8000

6000

H 4000

WILMINGTON,DEL.

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

5000

ALLENTOWN,PA.

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGURE 48. Total annual heating degree days for three stations in the Delaware River basin.
OfQ 

n>

3 

o

o

t!

O

Mi

n>

JU

5'

OfQ

OfQ

HEATING DEGREE DAYS (BASE 65 °F)

~\ I i I r sit

o c

"k

'"O"

o;" 

ro

HEATING DEGREE DAYS (BASE 65 °F) HEATING DEGREE DAYS (BASE 65 °F)

O - 10 CO

I I I I I I I I I I
52 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

PORTJERVIS, N.Y.

FREEZE-FREE SEASON

Another temperature-related climatic parameter 

relates not to the frequency with which a particular 

threshold value is exceeded but instead to the period of 

the year during which air temperatures remain above 

32 °F. It is often incorrectly termed the "frost-free" 

season. This term is inaccurate because frost formation 

occurs when the surface temperature, not the air 

temperature, reaches a critically low level and when atmospheric humidity and turbulence conditions are 

favorable. Frost will not always form when air 

temperature is below the freezing level. The freeze-free 

season is often equated with the growing season. Again, 

surface conditions are more important in determining 

growing conditions than is air temperature measured at 

screen height. Also, conditions favorable to growth vary 

according to plant species, so there is really no single 

definable growing season.

Graphs depicting the average length of the freeze-free 

season (fig. 50) and the average date of the last 32 °F 

temperature in spring, and first 32 °F temperature in 

fall (fig. 51) indicate substantial year-to-year variability.

Maps of these same three freeze-free season variables 

appear as figures 52-54.

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

BELVIDERE, N.J.

200 

190 

180 

170 

160 

150 

140 

130 

120 

110 -I I I I I I I I I I I I I I I I I I I I I I I I I I I I I L

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

GEORGETOWN, DEL. INDIAN MILLS, N.J.

210

200

190

180

170

160

150

140

130

120

110

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGURE 50. Daily length of the freeze-free season at four stations in the Delaware River basin, 1950-79.
53

PORT JERVIS, N.Y. INDIAN MILLS, N.J.

DATE OF 

FIRST 

32 =F 

READING 

IN FALL

DATE OF 

LAST 

32 F 

READING 

IN SPRING

* 

r

-

_

D 

C

ii

c

-

.E

-

-

-1

~

r

-|

"

r

-r

j-

-

,

DEC 1

NOV 1 DATE OF 

FIRST

"}9 "F 

OPT 1 

ULI n READING 

IN FALL 

SEPT 1

AUG 1 

JULY 1

JUNE 1 DATE OF 

LAST

MAY 1 32 'F 

READING 

IN SPRING 

APR 1

MAR 1 

FEE 1

1AM 1

-

-

_

~~*

-

~

~

~

-

~

~

|-

-

-

-

-

-

-

DEC1 

NOV 1 

OCT1 

SEPT 1 

AUG 1 

JULY 1 

JUNE1 

MAY 1 

APR1 

MAR 1 

FEE 1

1AM 1

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

BELVIDERE, N.J. GEORGETOWN, DEL.

DATE OF 

FIRST 

32 >F 

READING 

IN FALL

DATE OF 

LAST 

32 3F 

READING 

IN SPRING

- -

-

-

-

~

~

-

~

~

~

_

-

"

-

_

_

-

-

-

_

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

DEC 1 

DATE OF 

NOV 1 FIRST 

32 C F

READING 

OCT 1 | N FALL

SEPT1 

AUG 1 

JULY1

JUNE1 

DATE OF

MAY 1 3^SFT 

READING 

APR 1 IN SPRING

MAR1 

FEB1 

JAN 1

-

_ -

-

-1

-i

_

-

-

-

_

-

-

-

- -

-]

-

-

-

_

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

DEC1 

NOV1 

OCT1 

SEPT1 

AUG1 

JULY 1 

JUNE1 

MAY 1 

APR 1 

MAR 1 

FEB1 

JAN 1

FIGURE 51. Daily last minimum temperature in spring and first minimum temperature in fall at four stations in the Delaware

River basin, 1950-79.
54 CLIMATIC ATLAS OF THE DEI AWARE RIVER BASIN

EXPLANATION

Date

After May 10 

April 30 - May 10 

April 20 - 30 

April 10-20 

Before April 10

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

" FIGURE 52. Areal distribution of the average date of the last 

spring minimum temperature in the Delaware River basin.
TEMPERATURE 55

EXPLANATION

Date

V""' h*3^ %' ^ ifjzs*>-n >« >-"«

1. ***""TL IJf^^ 7*7" "^f" ^Jl V^ 1 " . ^HO>AA- ' if--sr,/-V

' ' ' w3 X ""\ ^*( Lebanon >s -> ^" ^

! "^^^ £/^' P

1 -^ ^-' V * i*;~ np

After Oct. 27 

Oct. 17-27 

Oct. 7-17 

Sept. 27 - Oct. 7 

Before Sept. 27

50 MILES

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 53. Areal distribution of the average date of the earliest fall minimum temperature in the Delaware River basin.
56 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

EXPLANATION

Number of days

50 MILES

50 KILOMETERS

' ~ SJ,/ S S 

UMTED STATES BASE MAP. 197o .

 »»

" FIGURE 54. Areal distribution of the average length of the 

freeze-free season in the Delaware River basin.
PRECIPITATION 57

PRECIPITATION

Although average monthly precipitation values indicate little seasonality in amount, there is a distinct 

seasonality in precipitation-producing mechanisms affecting the Delaware River basin. Migrating cyclonic 

systems are of greatest importance during the winter 

months. As the polar front shifts northward, during the 

warm season, moist Atlantic or gulf air is circulated into 

the region by the subtropical high pressure systems. 

Because of the convective nature of the resulting 

precipitation, summer rainfall patterns are less continuous than those of winter. Contributions by hurricanes and other systems of tropical origin are also included in warm season precipitation, in some years.

The most important local influence on precipitation 

receipt is terrain. Forced lifting of a moist air mass often

leads to precipitation on one side of a ridge and a 

precipitation "shadow" effect on the other. Within the 

Delaware River basin, the rugged Catskills have a 

3,500-foot elevation range and are associated with complex precipitation patterns. Terrain effects are also important in the other upland areas of the basin (fig. 55). 

Maps and time series plots are provided for monthly 

and seasonal precipitation values. In each case considerable year-to-year variability is evident. The mean 

and median values of the time series are presented with 

each graph. Often a marked difference exists between 

the two values because the distribution of precipitation 

values for a station is bounded by zero and tends to be 

positively skewed. The median precipitation value for 

many applications would be more representative of 

average precipitation conditions than would the calculated mean.

FIGURE 55. Northeast-trending ridges at Palmerton, Pa., which are the significant landforms of the ridge-and-valley area of

the Delaware River basin.
58 CLIMATIC ATLAS OF THE DEI AWARE RJVER BASIN

AVERAGE ANNUAL PRECIPITATION

Average annual precipitation values range from 40 to 

50 in. throughout the basin (figs. 56 and 57). The greatest 

spatial variability in average precipitation exists in the 

northern part of the basin, where terrain elements are 

significant.

The time series plots (fig. 56) indicate a range in annual totals of 28.68 in. at Georgetown, Del., 35.04 in. 

at Indian Mills, N.J., 35.69 in. at Belvidere, N.J., and 

26.07 in. at Hawley, Pa.

20

HAWLEY, PA.

MAXIMUM 53.24 INCHES 

MINIMUM 27.17 INCHES 

MEDIAN 38.68 INCHES 

MEAN 40.06 INCHES 

STANDARD DEVIATION 7.16 INCHES

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

70

60

- 30

INDIAN MILLS, N.J. 

MAXIMUM 64.44 INCHES 

MINIMUM 29.40 INCHES 

MEDIAN 44.97 INCHES 

MEAN 45.12 INCHES 

/STANDARD DEVIATION 8.06 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

60

10

BELVIDERE, N.J.

MAXIMUM 64.78 INCHES 

MINIMUM 29.09 INCHES 

MEDIAN 45.66 INCHES 

MEAN 45.66 INCHES 

/STANDARD DEVIATION 8.28 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

30

20

GEORGETOWN, DEL. 

MAXIMUM 57.89 INCHES 

MINIMUM 29.21 INCHES 

MEDIAN 41.86 INCHES 

MEAN 43.89 INCHES 

STANDARD DEVIATION 6.74 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 56. Average annual precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 59

EXPLANATION

Precipitation, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY | 

UNITED STATES BASE MAP, 1970 

^; . . i - r i r, p1GURE 57 Areal distribution of average annual precipitation

in the Delaware River basin.
60 CLIMATIC ATIAS OF THE DELAWARE RIVER BASIN

AVERAGE DECEMBER PRECIPITATION

Average December precipitation ranges from 2.79 in. 

to 5.00 in. within the basin (figs. 58 and 59).

The high precipitation totals of December 1973 were 

related to a deep trough in the Central States 

(Taubensee, 1974). The dryness of December 1965 was 

due to the East-Coast trough being displaced to the east 

of its normal position along the coast (Dickson, 1966).

15

14

13

11

10

9

8

w

o

^ 6

5

3

2

1

n

-

_

-

-i

_

-

HAWLEY, PA.

MAXIMUM 7.36 INCHES

MINIMUM

MEDIAN

MEAN

0.75 INCHES

3.22 INCHES

3.40 INCHES

/STANDARD DEVIATION 1.65 INCHES

k [ ,

~

-

-

-

_

/

/

 

/

/

 I

 I- -I

[-1

-

-

-

_:

-

15

14

13

11

10

9

8

w

o

- 6

5

4 

3

2

1

n

-

_

-

_

INDIAN MILLS, N.J.

- MAXIMUM 9.28 INCHES

MINIMUM 0.24 INCHES

MEDIAN 3.64 INCHES 

MEAN 4.12 INCHES

/STANDARD DEVIATION

_

-

-

-

-

-

-

/

/

/

/

/

, ,

_

| 

201 INCHES

! !

I 

-

_

-

_

-

-

 -

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12

11 

10 

9

7

5 

4 

3

2

1 

n

-

-

-

-|

-

-

BELVIDERE, N.J.

MAXIMUM 8.22 INCHES 

MINIMUM 0.83 INCHES 

MEDIAN 3.91 INCHES 

MEAN 3.84 INCHES 

/STANDARD DEVIATION 1.79 INCHES

-

-

-

pn -

/

-

/

|-|

/

1 

-

_

_

-

-

-

-

-

-

15

14

13

12

11 

10 

9

w

LLJ

I 7 

O

5 

4 

3

2

1 

n

r

-

-

-

-

-

-

-

GEORGETOWN, DEL 

MAXIMUM 7.99 INCHES 

MINIMUM 0.70 INCHES 

MEDIAN 3.38 INCHES 

MEAN 3.64 INCHES

/STANDARD DEVIATION 1 73 INCHES

-1

-

-

/

_

-

-

ipn

~

__

-

-|

-

-

 I

-

_!

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 58. Average December precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 61

EXPLANATION

Precipitation, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 59. Areal distribution of average December precipitation in the Delaware River basin.
62 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE JANUARY PRECIPITATION

Average January precipitation totals range from 2.40 

in. to 4.20 in. with the highest average values occurring 

in the northern part of the basin (figs. 60 and 61).

The annual time series plots (fig. 60) indicate great 

variability in individual monthly totals. At all stations, 

1978 and 1979 stand out as the 2 years of maximum 

January precipitation. Persistent upper air flow during 

these months resulted in the steering of a series of 

cyclonic systems along the Atlantic Coast. Warm, moist 

air moving over the Atlantic Ocean surface clashed with 

cold continental air to produce record snowfall and 

precipitation amounts along the East Coast.

15

14

13

12

11

10

9

8

I 7

CJ

- 6 

5 

4 

3

2

1 

n

-

-

-

-

-

-

-

-

-

-

HAWLEY, PA. 

MAXIMUM 7.56 INCHES

MINIMUM

MEDIAN 

MEAN

0.62 INCHES

2.66 INCHES 

2.97 INCHES

/STANDARD DEVIATION 1.60 INCHES

_

-

-

-

-|

-t

-

/

-

/

/

-|

"|-

pi

-

-

-

-

15

14

13

12

11

10

9

8

IT

CJ

5

4 

3

2

1 

n

-

-

-

"

-

-

INDIAN MILLS, N.J. 

MAXIMUM 8.90 INCHES

MINIMUM

!_ MEDIAN 

MEAN

0.50 INCHES

3.06 INCHES 

3.51 INCHES

/STANDARD DEVIATION

-

-

-

 |/

I

1

1

-

1.81 INCHES ,_!

 =1

-

=

-

_ _

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1 

n

-

-

-

-

_

-

-

-

-

-

_

-

BELVIDERE, N.J. 

MAXIMUM 9.97 INCHES

MINIMUM

MEDIAN

MEAN

0.55 INCHES

3.04 INCHES

3.33 INCHES

/ STANDARD DEVIATION 1.86 INCHES

-

-

_

-

-

, 

 |

/

~f

/

p

-

_

p

_

Hn

 |

i 

n

-

-

-

-

-

-

_

-

-

15

14

13

12

11

10

9

8

C/3

3; 7

5

4

3

2

1 

n

-

-

"

-

-

-

GEORGETOWN, DEL.

MAXIMUM 6.99 INCHES

MINIMUM 0.55 INCHES

MEDIAN 2.67 INCHES 

MEAN 3.30 INCHES

-

-

-

-

_

-\

/

-

/

/

h

/

/

STANDARD DEVIATION

 |

PI

-

1 67 INCHES

-

_

, !

 I ~

-

-

-

-

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 60. Average January precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 63

/ % o /fc~»

Z: _V_ ~ ,.'./ ..Jb

Lebanon >s

J-^r*/ ^v^^w: f^- ^:^

EXPLANATION

Precipitation, in inches

25

_L

50 MILES 

J

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY |' 

UNITED STATES BASE MAP, 1970 -

SUSS -

'"' FIGURE 61. Areal distribution of average January precipitation 

in the Delaware River basin.
64 CLIMATIC ATIAS OF THE DELAWARE RIVER BASIN

AVERAGE FEBRUARY PRECIPITATION

Average February precipitation values range from 2.30 

in. to 3.70 in. (figs. 62 and 63), with the higher values 

occurring along the eastern margin of the basin.

15

14

13

12

11

10

9

8

7 

5

4 

3 

2

1

0

-

-

-

-

-

-

-

-

HAWLEY, PA. 

MAXIMUM 5.06 INCHES

MINIMUM 0.15 INCHES

MEDIAN 

MEAN

Z.43 INCHES 

2.69 INCHES

/ STANDARD DEVIATION

-

-

-

-

2.

50 52

/

/

54

/

/

n

56 58 60 62 64 66

1.16 INCHES

~LJ

68 70 72

f

74 76

p

78

YEARS

15

14

13

12

11

10 

9

8

7

5

4 

3 

2 

1

n

_

-

-

-

-

BELVIDERE, N J

MAXIMUM 

MINIMUM

-

p

-

15

14

13

12

11

10

9

8 

to

£7 

0

5

4 

3 

2

1 

0

-

-

-

-

-

INDIAN MILLS, N.J.

MAXIMUM 6.32 IMCHES 

MINIMUM 1.34 IMCHES

MEDIAN 3.12 INCHES 

MEAN 3.35 INCHES

/STfi

~r\_L

-

NDARD DEVIATION 1 37 INCHES

~ | ~~ ~~

_

50 52 54 56 58 60 62 64 66 68

YEARS

-

-

-

-

5.32 INCHES 

0.74 INCHES

MEDIAN 2.78 INCHES 

MEAN 3.05 INCHES 

/STANDARD DEVIATION 1.17 INCHES

 i

-|

/

"

/

p

-

'

¥

 i

_

-

-

15

14

13

12

11

10 

9

8 

w

LU

5

4 

3

2

1 

n

-

-

-

-

GEORGETOWN, DEL. 

MAXIMUM 6.42 INCHES 

MINIMUM 0.67 INCHES

MEDIAN 3.01 INCHES 

MEAN 3.05 INCHES 

/STANDARD DEVIATION 1 42 IMCHES

- /

~J/ n___J=

-

 

-

-i

70 72

_

-

74

-

-|

76

-

-

-

-

-

-

-

-

p

-

T78

-,

-

-

-

-

-

-

-

50 52 54 56 58 60 62 64 66 TV

YEARS

70 72 74 76 78 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 62. Average February precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 65

EXPLANATION

Precipitation, in inches

 ' j-i * * i *>J? *^'V x- rf\

V ^y °\ i /v1 *v ^

g^ x°<*.14* M, <

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

'' SUSS ^'5Q'Cvy-v""'A R" '' FIGURE 63. Area] distribution of average February precipitation in the Delaware River basin.
66 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE MARCH PRECIPITATION

Average March precipitation falls in the 2.65-in. to 

4.57-in. range (figs. 64 and 65); the higher values occur 

in the eastern and central part of the basin.

15

14

13

12

11

10 

9 

8

CO

£7 

o

^ 6

5 

4 

3 

2

1

n

-

-

-

-

h

-

-

-

-

-

HAWLEY, PA. 

MAXIMUM 5.84 INCHES 

MINIMUM 1.46 INCHES 

MEDIAN 2.99 INCHES 

MEAN 3.27 INCHES 

/STANDARD DEVIATION 1.17 INCHES

-

-

-

 I

-

-

/

/

/

_

-

-

-

-

-

_=

-

15

14

13

12

11

10 

9 

8

CO

LJJ

X 7 O

^6

5 

4 

3 

2

1 

n

-

-

-

-

-

-

-

-

-i

"

-

-

-

-

INDIAN MILLS. N.J. 

MAXIMUM 6.87 INCHES 

MINIMUM 1.07 INCHES 

MEDIAN 4.08 INCHES 

MEAN 4.08 INCHES 

/STANDARD DEVIATION 1.28INCHES-

-

/

-

-

| 1 -

I- -

~

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12

11 

10 

9 

8

5 

4 

3 

2

1 

n

-

-

-

-

-

-

-

-

BELVIDERE, N.J. 

MAXIMUM 6.55 INCHES 

MINIMUM 1.70 INCHES 

MEDIAN 3.58 INCHES 

MEAN 3.68 INCHES 

/STANDARD DEVIATION 1.38 INCHES

- 1 1 / ~~~ ~ -

-

-

p

-

-|

-

q/

/

/

_

i -i

_P

-,

_

-

15

14

13

12

11 

10 

9 

8

CO

LU

O

5 

4 

3 

2

1 

n

-

-

-

-

-

-

-

-

n

 i 1

GEOR

MA) 

MIN 

MEC 

ME^ 

/STA

=

-

-

-

GETOWN, DEL. 

<IMUM 7.31 INCHES 

MUM 1.87 INCHES 

IAN 3.97 INCHES 

MM 3.87 INCHES 

NDARD DEVIATION 1.30 INCHES

-

-

-

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 64. Average March precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 67

42

EXPLANATION

Precipitation, in inches

1 ' " - ' \ /

j ''HO I _.f

1 JIM? » ^

^ -\

, Lebanon >s

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

'" FIGURE 65. Areal distribution of average March precipitation 

in
68 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE APRIL PRECIPITATION

Average April precipitation is greatest in the central 

area of the basin, where values generally fall into the 

4.00-in. to 4.40-in. range. Values taper off toward the 

north and south; minimum values are approximately 

3.00 in. (figs. 66 and 67).

15

14

13

12

11 

10 

9 

8

CO

£7 

o

5

4 

3

2

1 

n

-

-

-

-

-

-

-

-

HAWLEY, PA. 

MAXIMUM 6.27 INCHES 

MINIMUM 1.01 INCHES 

MEDIAN 3.17 INCHES 

MEAN 3.34 INCHES 

/STANDARD DEVIATION 1.35 INCHES

 /

-

~

-

^_

\ 

;

1

I

^^

|-|

_

pi -

-

-

-

-

15

14

13

12

11 

10 

9 

8

CO 

LLJ

x 7 

o

5

4 

3

2

1

n

-

-

-

-

-

-

-

-

INDIAN MILLS, N.J. 

MAXIMUM 7.01 INCHES 

MINIMUM 0.90 INCHES 

MEDIAN 2.23 INCHES 

MEAN 3.50 INCHES 

/STANDARD DEVIATION 1.54 INCHES

-

-

1 1

1

-

-

-

, |

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12 

11

10 

9 

8

CO 

LLJ

X 7 

o

5 

4 

3 

2

1

n

-

-

-

-

-

BELVIDERE, N.J. 

MAXIMUM 10.06 INCHES 

MINIMUM 0.74 INCHES

-

-

-

-

L

/

-

/

MEDIAN 3.57 INCHES 

MEAN 3.90 INCHES 

/STANDARD DEVIATION

r-

-

1.96 INCHES

-

-

 |

-

-

-

15

14

13

12 

11

10 

9 

8

CO

o

5 

4 

3 

2

1

n

-

-

-

_

-

-

-

~

GEORGETOWN, DEL. 

MAXIMUM 5.16 INCHES 

MINIMUM 0.90 INCHES 

MEDIAN 3.14 INCHES 

MEAN 3.09 INCHES 

/STANDARD DEVIATION 1 21 INCHES

-

-

/

/

-

/pi

-1

-|

-

l-l

1

p|

1 | _

p .

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 66. Average April precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION

EXPLANATION

Precipitation, in inches

DELAWARE >

,f-'l^

50 MILES

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

N R/I f:« pIGURE gy Areal distribution of average April precipitation in 

the Delaware River basin.
70 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN

AVERAGE MAY PRECIPITATION

Average May precipitation totals range from 3.10 in. 

to 3.6 in. in the central and eastern portions of the basin 

(figs. 68 and 69).

15

14

13

12

11

10

9

8

CO

£7 

o

5

4

3

2

1

HAWLEY, PA.

MAXIMUM 6.15 INCHES 

MINIMUM 0.85 INCHES 

MEDIAN 3.90 INCHES 

MEAN 3.53 INCHES 

STANDARD DEVIATION 1 50 INCHES

INDIAN MILLS, N.J. 

MAXIMUM 8.10 INCHES 

MINIMUM 0.75 INCHES 

MEDIAN 3.25 INCHES 

MEAN 3.40 INCHES 

STANDARD DEVIATION 1 75 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

15

14

13

12

11

10

9

BELVIDERE, N.J.

MAXIMUM 7.00 INCHES 

MINIMUM 0.40 INCHES 

MEDIAN 3.77 INCHES 

MEAN 3.64 INCHES 

^STANDARD DEVIATION 1 71 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

GEORGETOWN, DEL. 

MAXIMUM 6.63 INCHES 

MINIMUM 0.19 INCHES 

MEDIAN 3.07 INCHES 

MEAN 3.32 INCHES 

STANDARD DEVIATION 1 68 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 68. Average May precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 71

i /., Wes* /jfr v ' 

£ ? «+«4te;,<X^Mprt:r

Vfifi 

\°1, J'* 

^SRX^' 

(K ;SAte^- % NEW teEY ^

y

/ 

,^/fHf^f;Jx 

^<~, I Ij rn v tx ' ' K. i i, 

AV

\ ^ 

N

^.y 

^W

d^i A^ B Lianding

\

\

* .-x? f*-*/ o-'i/

^

' ^ff^' { \ 

. '~& Of

(Jape M?y

eniopen

i :f^

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

Geergeft

EXPLANATION

Precipitation, in inches

25

I

50 MILES

J

I 

25 50 KILOMETERS

, S U S S E*X^S$v /I FIGURE 69. Areal distribution of average May precipitation in

the Delaware River basin.
72 CLIMATIC: ATI AS OF THE DEI AWARE RIVER BASIN

AVERAGE JUNE PRECIPITATION

Average June precipitation values range from 3.22 in. 

to 4.56 in. (figs. 70 and 71).

June 1964 was a dry month throughout the basin. A 

mean ridge was located over the Appalachians and a 

deeper than normal trough existed to the east. The 

Delaware River basin was in the low-precipitation portion of the upper level wave form (Dickson, 1964).

High June precipitation amounts in 1972 were 

associated with Hurricane Agnes.

15

14

13

12

11

10

9

8

VI

17 

o

^ 6

5 

4 

3 

2

1 

n

-

-

-

-

-

HAWLEY, PA. 

MAXIMUM 10.77 INCHES

MINIMUM 0.93 INCHES

MEDIAN 2.95 INCHES 

MEAN 3.37 INCHES 

/STANDARD DEVIATION 2.32 INCHES

-

3-1

-

-

L

/

/

-

^^

-

tf

|-

T-

-

-

-1

-]

-

-

.

-

-

-

-

-

-

15 [

13 -

12 r

11

10

9

8

C/3

LJJ

I 7 

o

^6

5 

4 

3 

2 

1 

n

-

-

-

-

INDIAN MILLS, N.J. 

MAXIMUM 6.69 INCHES

MINIMUM 

MEDIAN

- MEAN

0.55 INCHES 

3.23 INCHES

3.28 INCHES

/STANDARD DEVIATION 1 59 INCHES

-

/

-

/

/

/

-

| I

|-

-

-

.-=

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12

11 

10 

9

C/3

LJJ

X 7 

O

5 

4 

3

2

1 

n

-

-

- -

BELVIDERE, N.J.

MAXIMUM 8.51 INCHES 

MINIMUM 1.08 INCHES 

MEDIAN 3.44 INCHES 

MEAN 3.82 INCHES 

/STAN DAR DDEVIATION 1.92INCHES

-

-

 .

~f

/

 

T

rn | -:

-

-i -

_^

-

-

15

14

13

12

11 

10 

9

LJJ

X 7 

O

5 

4 

3

2

1

n

-

-

-

-

GEORGETOWN, DEL. 

MAXIMUM 9.24 INCHES 

MINIMUM 0.55 INCHES 

MEDIAN 3.55 INCHES 

MEAN 3.64 INCHES

/^TANDARD DEVIATION 1.75 INCHES

-

-

-

-

/

/

-

p

p. rn

-

_

-

-i

-

-

-

-

-

-

-

-

 -

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 70. Average June precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 73

EXPLANATION

Precipitation, in inches

, . - ^ .J :

fe f^ © O Ivf/r-T] D E4_ AW A R E^

'\\£*#: -»****& I

V ATLANTIC

50 MILES

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

Yf "^ Kn Kft FIGURE 71. Areal distribution of average June precipitation in
CLIMATIC ATIAS OF THE DELAWARE RIVER BASIN

AVERAGE JULY PRECIPITATION

Average July precipitation ranges from 3.23 in. to 4.95 

in. (figs. 72 and 73).

July 1969 stands out (fig. 72) as a month of extremely 

high precipitation amounts at all stations in the basin. 

During that month a persistent mean trough developed 

in the East and resulted in heavy precipitation in the 

Atlantic Coast States. Allentown, Pa., received 4.54 in. 

of rainfall during one 24-hour period and had a total 

rainfall that month of 10.42 in., making July 1969 the 

wettest there since records began in 1912 (Andrew, 1969).

HAWLEY, PA.

MAXIMUM 7.99 INCHES 

MINIMUM 0.63 INCHES 

MEDIAN 3.12 INCHES 

MEAN 3.23 INCHES 

STANDARD DEVIATION 1 63 INCHES

INDIAN MILLS, N.J. 

MAXIMUM 10.89 INCHES 

MINIMUM 0.20 INCHES 

MEDIAN 3.96 INCHES

MEAN 4.23 INCHES

i

STANDARD DEVIATION 2 47 INCHES

n

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12

11

10

9

8

COLU

I 7 

O

BELVIDERE, N.J.

MAXIMUM 10.82 INCHES 

MINIMUM 0.77 INCHES 

MEDIAN 3.48 INCHES 

MEAN 4.43 INCHES 

/STANDARD DEVIATION 2.75 INCHES

15

14

13

12

11

10

9

8

COLU

I 7 

O

GEORGETOWN, DEL. 

MAXIMUM 12.97 INCHES 

MINIMUM 0.37 INCHES 

MEDIAN 3.32 INCHES 

MEAN 4.15 INCHES 

/STANDARD DEVIATION 2 69 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGURE 72. Average July precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 75

\

^

V,

-Si, /

<r v--"""' ' r*

V~J ^ >*

l NO'AL' J

; cMENAM&Oi 7 5" x"""^ %, ) 74

r?:-\-# ) ^ ^ \\-r~-m

' ' ^ ^" iDeih, , ^

,0 O N^1 H DEL AJW ARE *" ^ "^f , ff 

"\ -}K -../-/ >- ^?^ _, ;,,,: .-f<

EXPLAIMATIOIM

Precipitation, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

Gecrgetf^l

S S ^J^SJ^ v'.'/l FIGURE 73. Areal distribution of average July precipitation in

the Delaware River basin.
CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE AUGUST PRECIPITATION

Average August precipitation ranges from 3.20 in. to 

over 5.00 in. within the basin (figs. 74 and 75).

On each of the time series plots (fig. 74), August 1968 

appears exceptionally dry. This was due to the 

dominance of a strong ridge over the Eastern United 

States during the month (Andrews, 1968).

7 

w

£6 

o 

^ 5

4

3

2

1

0

HAWLEY, PA.

MAXIMUM 18.09 INCHES 

MINIMUM 0.57 INCHES 

MEDIAN 3.30 INCHES 

MEAN 3.95 INCHES 

STANDARD DEVIATION 3 08 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

15

14

13

12

11

10

9

8 

W

17 

O

5 

3

2

1 

n

INDIAN MILLS, IM.J. 

MAXIMUM 11. 43 INCHES

MINIMUM 0.65 INCHES

MEDIAN 3.95 INCHES 

MEAN 5.04 INCHES 

/STANDARD DEVIATION 3.45 INCHES

/

- /

- I

-

-

/

-

-

-

|- -|

pfT -

T

-

-

-^

-

-

-

-

-

-

76 78 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

BELVIDERE, N.J.

15

14

13

12

11

10

9

8 

w

17 

O

 6

5

4

3

2

1 

n

MAXIMUM 11.06 INCHES

-

-

MINIMUM 

MEDIAN

MEAN

1.28 INCHES 

4.14 INCHES

4.83 INCHES

/STANDARD DEVIATION 2.78 INCHES

-

-

-

-

-

-

_

-

-

_

/-

/

_r

-

-

-

-

-

r-

_.

_

-

-

-

-

_

-

-

-

-

15

14

13

12

11

10

9

8

w 

x 7

o

? 6

5

4

3

2

1 

n

GEORGETOWN, DEL.

MAXIMUM 14.15 INCHES

MINIMUM 1.06 INCHES 

MEDIAN 4.34 INCHES

-

-

-

-

-

-

-

-/

-

-

-

-

-

MEAN 5.38 INCHES

/STANDAR

/

-

DDEVIATION 3.40 INCHES

-

-

r-

-

-

-

-

-

-

-

-

-

- -;

-

-

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGURE 74. Average August precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 77

EXPLANATION

Precipitation, in inches

5.2

£

50 MILES 

I

50 KILOMETERS

\

'" ^-- \ ,, A-- / <r?"7 ,- * «~/ BA l b$

^f^" \ \ Capr May 

"^0

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

 vr«M -, , £ s FIGURE 75. Areal distribution of average August precipitation

in the Delaware River basin.
78 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN

AVERAGE SEPTEMBER PRECIPITATION

Average September precipitation ranges from 3.29 in. 

to 4.72 in. (figs. 76 and 77).

The low precipitation received throughout the basin 

in September 1970 was the result of an upper level mean 

ridge affecting eastern States (Taubensee, 1970). Hurricane Eloise contributed to the high precipitation totals 

of September 1975 in the southern part of the basin. Hurricane Donna produced high precipitation amounts in 

September 1960.

15

14

13

12

11 

10

9

8

CO

£7 

o

- 6

5 

4 

3

2

1 

n

-

-

-

-

HAWLEY, PA.

MAXIMUM 7.83 

MINIMUM 1.19

INCHES 

INCHES

MEDIAN 3.34 INCHES 

MEAN 3.51 INCHES 

/STANDARD DEVIATION 1.53 INCHES

-

-y

-

/

/

/

/

n

pn

_r n

_

-

-

_

I-

-

-

-

-

-

-

15

14

13

12

11 

10

9

8

CO

LU

I 7

O

- 6

5 

4 

3

2

1 

n

- ~

INDIAN MILLS, N.J. 

MAXIMUM 9.44 INCHES

MINIMUM 0.65 INCHES

MEDIAN 3.20 INCHES 

MEAN 3.54 INCHES

/STANDARD DEVIATION 2.23 INCHES

-

-

-

-J_

-

-

/

-

/

/

- _

T

 |

-

p-

-

~

, |

-

 -

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13 

12

11 

10

9

8

CO

I 7 

o

5 

4 

3

2

1 

n

-

-

BELVIDERE, N.J.

-|

-

MAXIMUM 7.84 INCHES 

MINIMUM 1.24 INCHES 

MEDIAN 3.82 INCHES 

MEAN 4.14 INCHES 

/STANDARD DEVIATION 1.84 INCHES

-

-

-

L

-

1

/

/

i 

-

 i

i 

p-

-

-1

-

-

-

-

_

-

-

15

14

13 

12

11 

10

9

8

CO

I 7 

o

5 

4 

3

2

1 

n

-

-

"

-

GEORGETOWN, DEL. 

MAXIMUM 8.62 INCHES 

MINIMUM 0.60 INCHES 

MEDIAN 3.63 INCHES 

MEAN 3.59 INCHES 

/STANDARD DEVIATION 1.89 INCHES

-

-

-

-

-

L

1

/

_

-i

-

rrp

rr

p-

-

-

p

-

-

- "

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78 50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

FIGURE 76. Average September precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 79

\o-3i> * r'kt,-.-, -5 '«'.. ~-\^k\ ' V " "' -

^o 41 %- Y SALEM \% MEW jees-EY ^/

%-4^j^-V>< A^HT^^ N^M H mf, r ^r:d*.-to>> x v*.^, (?iy

BASE FROM U.S. GEOLOGICAL SURVEY | 

UNITED STATES BASE MAP, 1970 L

EXPLANATION

Precipitation, in inches

25

I

50 MILES 

I

25 50 KILOMETERS

FIGURE 77. Areal distribution of average September precipitation in the Delaware River basin.
80 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

AVERAGE OCTOBER PRECIPITATION

Average October precipitation values range from 2.58 

in. to 4.59 in. (figs. 78 and 79).

October 1963 was a dry month throughout the 

Delaware River basin. During that month, the 

700-millibar heights were above normal, and minimal 

air flowed into the area from the Gulf of Mexico the normal source of moist air during October (Green, 1964).

15

14

13

12

11

10

9

8

£7

O

^ 6

5

4

3 

2

1 

n

-

-

-

-

-

-

-

HAWLEY, PA.

-

_

-

-

-

_

-

-

-

MAXIMUM 10.70 INCHES

MINIMUM

MEDIAN

MEAN

0.06 INCHES

2.83 INCHES

3.20 INCHES

/STANDARD DEVIATION 2.07 INCHES

/

, i/

rf _r

-

-

-

-

-

-

-

15

14

13

12

11

10

9

8

LU

x 7

o

- 6

5

4

3 

2

1 

n

-

-

-

-

"

-

-

-

INDIAN MILLS, N.J.

MAXIMUM 6.69 INCHES

MINIMUM 0.22 INCHES

MEDIAN 3.00 INCHES

MEAN 3.26 INCHES

/STANDARD DEVIATION 1 75 INCHES

-

-

-

-

-_

-

-

p.

/

/

~

/

/

UT

-

-

-

-

r-

 

-

-

-

-

 -

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

14

13

12

11 

10 

9

INCHES 0O) -J 

5

4

3

2

1 

n

-

-

-

-

-

-

-

-

-

;_

-

| 

-,

-

-

-

-

BELVIDERE, N.J. 

MAXIMUM 9.27 INCHES 

MINIMUM 0.13 INCHES 

MEDIAN 3.22 INCHES 

MEAN 3.31 INCHES

/STANDARD DEVIATION 1.84 INCHES

/

L

T

/

J

-

-

 

 | I 

 

-

~-

-

-

15

14

13

12

11 

10 

9

LU

5 7

5

4

3

2

1 

n

-

-

-

"

-

-

GEORGETOWN, DEL.

MAXIMUM 9.78 INCHES 

MINIMUM 0.09 INCHES 

MEDIAN 3.04 INCHES 

MEAN 3.29 INCHES 

/STANDARD DEVIATION 2.21 INCHES

-

-

-1

-'

-

-

/

^_^

/

-

/

 

1

_

 i

~L -

~|

-

 

-

-

-

-

-

 - - 

-

- '

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 78. Average October precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 81

42

EXPLANATION

Precipitation, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970 ,

WO

N 1% " ' FIGURE 79. Areal distribution of average October precipitation

in the tne ueiaware Dplawarp River Kiver basin oasin.
CLIMATIC ATLAS OF THK DELAWARK RIVKR BASIN

AVERAGE NOVEMBER PRECIPITATION

Average November precipitation ranges from 3.06 in. 

to 5.08 in. (figs. 80 and 81).

November 1972 was a wet month throughout the 

Delaware River basin. A deep trough in the central 

United States and a storm track south of normal produced high precipitation totals in the region (Dickson, 

1973).

November 1964 was a dry month at all Delaware River 

basin stations due to a persistent upper level ridge in 

the Eastern United States (Dickson, 1965).

15

14

13

12

11

10

9

8

w

£7

u

- 6

5

4

3

2

1 

n

-

-

_ HAWLEY, PA.

1 15

1 14

J 13 1

12

MAXIMUM 8.37 INCHES ;

MINIMUM 1.24.NCHES

MEDIAN 3.47 INCHES

MEAN 3.54 INCHES

/STANDARD DEVIATION 154 INCHES

-

-

-

-

-

-

-

* /

"

/

/

-

-

| |

-|

71

J 

1-

->, 11

-I 10

1

-\ 8

w

-

-

-

. |

-

-

-

x 7

u

- 6

5

4

3

2 

1

n

-

-

INDIAN MILLS, N.J.

MAXIMUM 9.56 INCHES

MINIMUM 0.48 INCHES

MEDIAN 3.45 INCHES

MEAN 3.76 INCHES

/STANDARD DEVIATION 2.23 INCHES

/

/

/

/

-

^

-

-

InzLa

- "T

HT

_

f

i-.

"

-

_

-

-

-

-

-

-

-

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 

YEARS

70 72 74 76 78

15

14

13

12

11 

10

9

8

jj 

x 7

5

4

3

2 

1 

n

-

-

-

BELVIDERE

-

-

-

, N.J.

MAXIMUM 8.51 INCHES 

MINIMUM 0.83 INCHES 

MEDIAN 3.39 INCHES

MEAN 3.87 INCHES 

/STANDARD DEVIATION 1 83 INCHES

-

-

--

-

-

J.

-

/

/

/

~

/

 |

/

Z^|

.-

r-|

--, p-

-

-

-

-

-

-

15

14

13

12

11 

10

9

8 

w

LLJ

x 7 

o

5

4

3

2

1 

n

-

-

-

-

GEORGETOWN DEL

-

-

-

-

MAXIMUM 6.26 INCHES 

MINIMUM 0.87 INCHES 

MEDIAN 3.22 INCHES

MEAN 3.32 INCHES 

/STANDARD DEVIATION 1 68 INCHES

-

-

-

~

-

-

1 1 /

J. -= " ~i "

T

 

-^

-

-

-

~- -

 _

>- :

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 80. Average November precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 83

EXPLANATION

Precipitation, in inches

.4

50 MILES 

I

^'T-4W^'"" C> '

' 1 H^ & ^ » i^^» k.

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

;rn- c.,

LU S S

$C I' " FIGURE 81. Areal distribution of average November precipitation in the Delaware River basin.
84 CLIMATIC ATIAS OF THE DELAWARE RIVER BASIN

AVERAGE WINTER PRECIPITATION

Average winter (December-February) precipitation 

ranges from 7.37 in. to 12.83 in. (figs. 82 and 83).

During the winter months of December 1978 through 

February 1979, the highest precipitation totals of the 

30-year period occurred at the three southernmost stations at the transect. Upper level circulation features of 

the 1978-79 winter were described in the section on 

average January precipitation.

20

HAWLEY, PA.

MAXIMUM 1292INCHES 

MINIMUM 3.20 INCHES 

MEDIAN 9.32 INCHES 

MEAN 8.93 INCHES 

STANDARD DEVIATION 2.18 INCHES

52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

25

20

10

INDIAN MILLS, N.J. 

MAXIMUM 17.07 INCHES 

MINIMUM 3.60 INCHES 

MEDIAN 11.37 INCHES 

MEAN 11.06 INCHES 

STANDARD DEVIATION 3.02 INCHES

52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

20

10

BELVIDERE. N.J.

MAXIMUM 15.71 INCHES 

MINIMUM 5.17 INCHES 

MEDIAN 9.93 INCHES 

N 10.16 INCHES 

STANDARD DEVIATION 2 65 INCHES

n

52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

25

20

o 10

GEORGETOWN, DEL. 

MAXIMUM 14.24 INCHES 

MINIMUM 4.50 INCHES 

MEDIAN 10.34 INCHES 

MEAN 10.11 INCHES 

STANDARD DEVIATION 2 75 INCHES

52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 82. Average winter (December-February) precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 85

1-:

V

Vi>

<t.

I" No rw n,i J 

' CMENAr^GO i 

' ' \

-o >

X°

75°x-~\ -fc j

^ v ' ^, ?

74° j>

42

EXPLANATION

Precipitation, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

 v'" N "" ''" FIGURE 83. Areal distribution of average winter (DecemberFebruary) precipitation in the Delaware River basin.
86 CLIMATIC \TIAS OFTHh DELAWARE RIYKR BASIN

AVERAGE SPRING PRECIPITATION

Average spring (March-May) precipitation ranges from 

9.01 in. to 13.55 in., with the highest values in the central and eastern parts of the basin (figs. 84 and 85).

Time series plots of spring precipitation are shown in 

figure 84.

15

HAWLEY, PA.

MAXIMUM 15.68 INCHES 

MINIMUM 5.18 INCHES 

MEDIAN 10.32 INCHES 

MEAN 10.12 INCHES 

STANDARD DEVIATION 2.58 INCHES

n

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

25

20

10

INDIAN MILLS, N J.

MAXIMUM 17.85 INCHES 

MINIMUM 6.95 INCHES 

MEDIAN 10.80 INCHES 

MEAN 11.01 INCHES 

/STANDARD DEVIATION 3.12 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

25

BELVIDERE, N.J.

MAXIMUM 20.47 INCHES 

MINIMUM 5.65 INCHES 

MEDIAN 11.07 INCHES 

MEAN 11.18 INCHES 

''STANDARD DEVIATION 3.24 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

O 10

GEORGETOWN, DEL. 

MAXIMUM 15.88 INCHES 

MINIMUM 5.80 INCHES 

MEDIAN 9.72 INCHES 

MEAN 10.26 INCHES 

STANDARD DEVIATION 2.63 INCHES

n

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 84. Average spring (March-May) precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 87

EXPLANATION

Precipitation, in inches

12.0

11.0

10.0

50 MILES 

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

UNITED STATES BASE MAP, 1970 -L ^

if/ wi tH pIGURF §5 Areal distribution of average spring (March-May) 

precipitation in the Delaware River basin.
88 CLIMATIC ATI AS OF THE OKI AWARE RIVER BASIN

AVERAGE SUMMER PRECIPITATION

Average summer (June-August) precipitation (figs. 86 

and 87) ranges from 10.51 in. to 13.92 in. Figure 86 

shows the yearly values of summer precipitation for the 

four representative stations.

HAWLEY, PA.

MAXIMUM 23.25 INCHES

MINIMUM 4.21 INCHES

-

-

-

|-

| | MEDIAN 10.50 INCHES

MEAN 10.55 INCHES

-

/STAND

-

-

 1

-

-

ARDDEV

-

Al IO VI 1 .31 IN CHES "

--

50 52 54 56 58 60 62 64 66 

YEARS

25

20

15

10

INDIAN MILLS, N.J.

MAXIMUM 22.58 INCHES 

MINIMUM 4.61 INCHES 

MEDIAN 12.43 INCHES

pn

-,-

r~

-i

-

-

1

l_

1

M

/s^

EA 

AFV

M 

Dfi RC

12 

DE

.63 

-Vl>

IN 

Ml

CH

ON

ES 

4 68 INC:HE s

70 72 74 76 78 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

25

20

15

10

BELVIDERE, N.J.

MAXIMUM 24.18 INCHES 

MINIMUM 5.43 INCHES 

MEDIAN 12.26 INCHES 

MEAN 13.18 INCHES 

/STANDARD DEVIATION 4.75 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

0 10

GEORGETOWN, DEL. 

MAXIMUM 25.18 INCHES 

MINIMUM 6.07 INCHES 

MEDIAN 13.08 INCHES 

MEAN 13.25 INCHES 

STANDARD DEVIATION 4 54 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 86. Average summer Gune-August) precipitation at four stations in the Delaware River basin, 1950-79.
PRF.CIPI TATIOX 89

EXPLANATION

Precipitation in inches

/

DELAARE

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

" FIGURE 87. Areal distribution of average summer QuneAugust) precipitation in the Delaware River basin.
CLIMATIC, ATI AS OFTHK DEI AWARE RIVER BASIN

AVERAGE FALL PRECIPITATION

Average fall (September-November) precipitation (figs. 

88 and 89) ranges from 9.37 in. to 14.42 in.

Figure 88 shows the time series plots of fall precipitation for the four representative stations along the northsouth transect in the basin.

25

20

15

10

HAWLEY, PA.

MAXIMUM 17.44 INCHES 

MINIMUM 3.73 INCHES 

MEDIAN 10.41 INCHES 

MEAN 10.26 INCHES 

STANDARD DEVIATION 2.80 INCHES

10

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

INDIAN MILLS, N.J.

MAXIMUM 17.93 INCHES 

MINIMUM 4.36 INCHES 

MEDIAN 10 45 INCHES 

MEAN 10.58 INCHES 

/STANDARD DEVIATION 3.27 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

25

20

BELVIDERE, N.J.

MAXIMUM 17.04 INCHES 

MINIMUM 5.16 INCHES 

MEDIAN 11.32 INCHES 

MEAN 11.33 INCHES 

/STANDARD DEVIATION 3.12 INCHES

20

o 10

GEORGETOWN, DEL. 

MAXIMUM 18.81 INCHES 

MINIMUM 4.09 INCHES 

MEDIAN 10.56 INCHES 

/IEAN 10.20 INCHES 

/STANDARD DEVIATION 3.07 INCHES

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 88. Average fall (September-November) precipitation at four stations in the Delaware River basin, 1950-79.
PRECIPITATION 91

EXPLAIMATIOIM

Precipitation, in inches

V, i /'''SOSSBX/V

^ A

\ Easton / v-\ 

- AlientowrS \

50 MILES 

I

1 ' ' I

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

UNITED STATES BASE MAP, 1970 -,.

FIGURE 89. Areal distribution of average fall (SeptemberNovember) precipitation in the Delaware River basin.
92 CLIMATIC ATLAS OF THF DEI AWARE RIVER BASIN

SNOWFALL

Average annual snowfall increases from south to north 

within the Delaware River basin (figs. 90 and 91). 

Average yearly snowfall at Wilmington, Del., is 21.8 in.; 

Allentown, Pa., receives 32.5 in.; and Binghamton, N.Y., 

averages 85.1 in. The graphs on figure 91 indicate the 

monthly distribution of snowfall at the three stations.

BINGHAMTON, N.Y.

O *- C-J CO TJ- i

YEARS

WILMINGTON,DEL

80

o 60

IDLDLDLOLDLDLDLDlf) CD CO CO CO COCOCOCOCDCDr^-r^r^-

o * CNCO ^-LncDr^oo o o » CN co^incDr^ooooi cNco^-kDcop^oo 

YEARS

120

O 60

ALLENTOWN,PA.

YEARS

FK;URE 90. Total annual snowfall at three stations in the Delaware River basin, 1950-79.
PRECIPITATION 93

Great year-to-year variability in snowfall exists as indicated by the time series plots (fig. 90). During the 

1950-51 through 1978-79 seasons, annual totals at 

Wilmington, Del., range from 1.2 in. to 49.5 in.; 

Binghamton, N.Y., totals range from a minimum of 52.0 

in. to 122.6 in.

20

BINGHAMTON, N.Y.

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

WILMINGTON,DEL.

20

15

ALLENTOWN,PA.

20 1 I I I \ I

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

FIGURE 91. Average monthly snowfall at three stations in the Delaware River basin.
94 CLIMATIC; ATLAS OF THE DEI AWARE RIVER BASIN

BINGHAMTON, N.Y.

PRECIPITATION DAYS

Figure 92 shows for each of three first-order 

climatological stations the average number of days per 

month on which measureable precipitation amounts 

were recorded. The total number of precipitation days 

increases from south to north. Wilmington, Del., 

averages 116 days per year; the Allentown, Pa., station 

averages 123 days per year; and Binghamton, N.Y., experiences 163 precipitation days per year. Of the three 

stations, Binghamton, N.Y., exhibits the greatest degree 

of seasonality in the monthly precipitation day totals, 

with the maximum number during the December 

through March period. Binghamton's high annual 

precipitation day and the seasonality of precipitation are 

due to the frequent occurrence of migratory lows affecting the northern part of the basin. This low pressure 

system activity peaks during the winter months as the 

polar front shifts to its southernmost location.

15

< 10

"I I T

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

ALLENTOWN,PA.

20 iIIIIIIIIIT

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

WILMINGTON,DEL 

20 

15

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

FIGURE 92. Average monthly precipitation days at three 

stations in the Delaware River basin.
PRECIPITATION 95

BINGHAMTON, N.Y.

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT MOV DEC

ALLENTOWN,PA.

AVERAGE MONTHLY DEW-POINT TEMPERATURE

The dew point is calculated from psychrometric 

measurements made at first-order climatological stations. The graphs (fig. 93) show a slight decrease in 

average dew-point for each month along a south-to-north 

transect. This is a result of cooler average temperatures 

and the resulting diminished water vapor-holding 

capacity of the lower atmosphere along the transect. A 

seasonality in average dew-point temperature at each 

station is obvious. Again, this is a result of the annual 

course of air temperature and accompanying changes in 

the ability of the atmosphere to hold water vapor.

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

WILMINGTON,DEL.

70

60

b 50

LJJ

I

c 40

I

w 30

LJJ

LJJ

CC

O on

LJJ 20

D

10

0

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

FIGURE 93. Average monthly dew-point temperature at 

three stations in the Delaware River basin.
96 Cl JMATIC ATI AS OF THE DELAWARE RIVER BASIN 

CLOUD COVER THUNDERSTORM DAYS

Several measures of cloud cover are used in the 

climatic summaries published by the National Oceanic 

and Atmospheric Administration. The measurements 

plotted here involve classifying individual days into 

three categories based on daytime cloudiness. A day 

having 8 to 10 tenths cloud cover is considered "cloudy"; 

one having 4 to 7 tenths cloud cover is considered to be 

"partly cloudy"; and a day having 0 to 3 tenths cloud 

cover is classified "clear." Figure 94 shows the average 

percentage of days falling into these three categories by 

month for the 30-year period of study.

The total number of cloudy days per year increases 

from south to north, but the total clear days per year 

decreases. A definite seasonal component exists in these 

frequencies; at all stations there are more cloudy days 

in winter than in summer. This seasonality is most pronounced at Binghamton, N.Y.

The time series plots (fig. 95) depict the summer 

(June-August) and winter (December-February) percentages of clear days for the 30 years of records used in this 

study.

The graphs (fig. 96) indicate the average number of 

days per month during which thunderstorms occur. 

Thunderstorms are most common in the summer months 

when relatively intense surface heating combines with 

moist, unstable air masses to produce convectional 

storms.

BINGHAMTON, N.Y.

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

WILMINGTON,DEL. ALLENTOWN.PA.

80

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

EXPLANATION

| | Clear (0-3 tenths cloud cover)

Partly cloudy (4-7 tenths cloud cover) 

Cloudy (8-10 tenths cloud cover)

FIGURE 94. Monthly percentage of clear, partly cloudy, and cloudy days for three stations in the Delaware River basin.
PRECIPITATION 97

PERCENTAGE OF CLEAR DAYS (0-3 TENTHS CLOUD COVER) SUMMER

100 BINGHAMTON, N.Y.

80

0 J i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78

YEARS

PERCENTAGE CLEAR DAYS (0-3 TENTHS CLOUD COVER ) WINTER

100 BINGHAMTON, N.Y.

80

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

100 ALLENTOWN.PA.

80

40

20

i i i i i

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

100 i 

40

20

ALLENTOWN,PA.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

80

60

WILMINGTON,DEL.

0 J i

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

100 i 

60

WILMINGTON,DEL.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 95. Annual percentage of clear summer and winter days at three stations in the Delaware River basin, 1950-79.
98

BINGHAMTON, N.Y.

6

5 

4

3

2

0

1

_

1 1

-

-

-

_

1

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

ALLENTOWN.PA.

7 

6

5 

4 

3 

2 

1

1 1

-

1

~^

WILMINGTON,DEL

7

6

5

3

2

1

I

-

-

-

-

__, 

1

-

-

-

-

1 

JAN FEE MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

FIGURE 96. Average days per month of thunderstorm occurrence at three stations in the 

Delaware River basin.

CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

CLIMATIC WATER BUDGET

The preceding discussions have treated climatic 

variables individually, without consideration of the 

covariability of these terms in any fashion. One method 

of climatological analysis that does incorporate several 

climatic variables involves the calculation of water 

budgets.

Water-budget studies may be done at spatial scales 

ranging from local to global and at temporal scales 

ranging from daily to annual. The analyses presented 

here were performed on a monthly basis for individual 

climatic stations; the explanation that follows focuses 

on these scales.

In water-budget analysis, precipitation is treated as input or "supply" to the environmental system. The 

primary "demand" is evaporation and transpiration, 

termed evapotranspiration. Potential evapotranspiration 

is defined as the amount of evapotranspiration occurring 

over a continuous vegetated surface with an abundant 

soil-moisture supply. It is a function of the amount of 

energy available to accomplish evapotranspiration.

In monthly water-budget calculations, when precipitation exceeds potential evapotranspiration, the actual 

evapotranspiration for that month is considered equal 

to the potential amount. Excess water may be stored as 

soil moisture until the soil-moisture storage reaches an 

upper limit, known as the field capacity. Any additional 

precipitation excess is termed water surplus and may 

contribute to runoff or ground-water storage.

During a month when potential evapotranspiration exceeds precipitation, all precipitation goes toward actual 

evapotranspiration. Some water stored as soil moisture 

is also extracted to satisfy the climatic water demand. 

The contributions of precipitation and soil moisture to 

the actual evapotranspiration usually do not meet the 

entire water demand represented by the potential 

evapotranspiration. The difference between the actual 

evapotranspiration and the potential evapotranspiration 

is termed the water deficit for that month.

These basic water-budget calculations have been 

adapted for use in a variety of applications. Chief among 

these are agricultural studies, for which water budgets 

have been used for irrigation-scheduling and crop-yield 

predictions (fig. 97). Many hydrologic studies have incorporated water-budget calculations to forecast runoff and 

ground-water levels.

Calculation of Water-Budget Terms. The general waterbudget approach described above and the procedures 

used in the calculation of the water-budget terms were 

developed by Thornthwaite (1948). More recently, Mather 

(1978) has elaborated on these procedures and has 

described many applications of water budgeting to problems in environmental analysis.
WATER BUDGET FOR THE DELAWARE RIVER BASIN 99

Actual water-budget calculations require (1) long-term 

average monthly air-temperature data, (2) station 

latitude, (3) monthly temperature and precipitation data 

for the period of analysis, and (4) maximum possible soil 

moisture storage in the plant root zone. First, the annual heat index / is calculated by

12 (1)

where ti = the long-term average temperature for the 

ith month of the year. The annual heat index, in turn, 

is used to evaluate the parameter a:

a = 6.75 x 10~ 7 / 3 -7.71 x 10~ 5 I 2

+ 1.792 x 10~2 7+0.49239. (2) 

The heat index and the parameter a were used by 

Thornthwaite to relate empirically collected evaporation 

data to air temperature. The monthly potential evapotranspiration (e) in centimeters is calculated for a 

12-hour day, 30-day month by

10T "(T (3)

where Tis the monthly average temperature (°C). This 

unadjusted value is then corrected by allowing for the 

appropriate day length and number of days in a month. 

This final value is the monthly potential evapotranspiration.

Precipitation data are used directly in the waterbudget calculations and are compared to the calculated 

potential evapotranspiration data on a month-to-month 

basis. The final necessary piece of information for completion of the accounting procedure is related to the 

water-storage capability of the soil. This varies according 

to the soil texture; the finer textured soils have greater 

moisture-storage capacity than coarse textured soils. The

depth of the rooting zone of the plant cover also affects 

the total amount of water available for transpiration. 

Water-budget calculations have been made for all stations in the Delaware River basin that collect 

temperature and precipitation data. The purpose of this 

analysis is to provide a basis for comparison among these 

stations when climatic parameters derived from both 

temperature and precipitation are considered. All 

budgets have been calculated uniformly, assuming a 

maximum possible soil-moisture storage of 4.00 in. 

When soil-moisture stores are used to satisfy the potential evapotranspiration demand, it is assumed that the 

rate of water loss by the soil varies directly with the soil 

moisture content. A soil at field capacity readily releases 

water to transpiration; a soil nearly depleted of moisture 

does not readily release water. A final assumption relates 

to the treatment of precipitation that falls as snow. In 

the calculations that follow, all precipitation occurring 

in a month with average temperature of 32 °F or below 

(with zero potential evapotranspiration) is included as 

surplus for that month.

WATER BUDGET FOR 

THE DELAWARE RIVER BASIN

POTENTIAL EVAPOTRANSPIRATION

The maps that follow (figs. 98-107) depict average annual potential evapotranspiration and individual 

monthly average values for all months having potential 

evapotranspiration values significantly different from 

zero. The annual potential evapotranspiration values 

throughout the basin range from approximately 23 in. 

to 30 in. (fig. 108). The values are clearly a function of 

temperature, albeit a nonlinear relation.

FIGURE 97. Truck gardening in the southern New Jersey coastal plain.
100 CLIMATIC ATIAS OF THE OKI AWARE RIVER BASIN

EXPLANATION

Potential evapotranspiration, in inches

ptrrr \ M, 

1 l Mfe. \

I '*

,> - V--J -

1 < k H&fi

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

*" ' FIGURE 98. Average annual potential evapotranspiration in the 

Delaware River basin.
POTENTIAL EVAPOTRANSPIRATION 101

7f

A'

^ ^

;

" ^ 75-X-X; '°V )

 / \ X> v-ti >, ^Jr--^/ §|

Det^ / ,,£C/^ i ^ )

t o / Cetdkili'f 

DE^AJWARE^ ^C / r^^i

i , .s \ ; sheading i Lebanon ^.X | ^, ' /

EXPLANATION

Potential evapotranspiration, in inches

.2

i\Sandy

'K-Hook

, i H -.SSL r «ridteto^ ! N x \^av

Jj: r^>\{ Ox '- ' T Land"" r4,m VV,>^' . J

 -^»i v^ \. ^*s. ^^^ i ,i

BASE FROM U.S. GEOLOGICAL SURVEY

UNITED STATES BASE MAP, 1970 _

25 50 MILES

0 25 50 KILOMETERS

FIGURE 99. ^Average March potential evapotranspiration in the
102 CLIMATIC ATI AS OF THE DELAWARE RIVER BASIN

r--.

i, v~ j> 

\, ;V.,,* \ iikh.oo.a^.

EXPLANATION

Potential evapotranspiration, in inches

1.8 

1.6 

1.4

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 100. Average April potential evapotranspiration in the 

Delaware River basin.
POTENTIAL EVAPOTRANSPIRATION 103

I NprwicS- J

' CMENAf^SO 

76° ' *-o." 

I rrr~i ttf^i'' 

1 ' X^* 

4*, '

r-'

"~i

T 

1

>

y;:: *$k / o

,4 I ^o

75° S~--*4 \

/ v ' , r^, 

r-T '\ '

«», s* X- fie \

/

/

)

'^1-

 1 

t

If

r~ a

,-X -j 1 "-st-^

^ i DelJ** ' / .^

<* / / -C^'

74'

EXPLANATION

Potential evapotranspiration, in inches

IfjV^orrjS

i

ON {^

/

T-

,x- . v--~»

-X f

NllHdER*

fa^Nv. , __ ,

" T^

^ {

i /'*

***~++.

t^ iSandy

J,& -N^ook / C* - r^i

3

c

.b 

O. 9 A. f-r

 o 9

O. £-

 -a n

O. \J

- y^° i ^ ^. 'Treel- )lri /

/ C } '

i X*C4^ \^ »^a ; t^v J

4V-^\ ^"-i ^ /

f~-' ^ V -/V;

!

& °^

\ \ M'/

_.._.V4A.^...R^ef-. f->f|

 vx'"^ 

\ 2v/7

25

I

50 MILES

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 101. Average May potential evapotranspiration in the 

Delaware River basin.
104 CLIMATIC ATLAS OF THE DEI AWARE RIVER BASIN

-f

a;

r-..__. i.i ,4*

\ ^chAbaftst ~] 

A

 -1 , f /wo / 

}' Norwich5 J /". "*/

:CMENAH5oi 75,l<"^\ % J

r~£~( M-~ } s~* \ ^ i-

^ ! , «(V' - .< ., X.- . -^fi ._ j

<!1

-¥fs%^t i c4^--

^ ^ vv ? Z H /j<. .j ,~

V % "^ t

y 3 -Z i ^ ^ s-- > >^i^^ r

( vVilk^s-Sarre ! ^/*"""~ ^>

1 >'' /551 ^>v r^ L/ - SUSSEX.y '

'^Vf V AitAN

rr^ ^ ^ £^$^ ' - ^Mn

^ *r \ ® 

X? ^*

EXPLAIMATIOIM

Potential evapotranspiration, m inches

5.0 

4.8 

4.6 

4.4 

4.2

25 50 MILES

I 

25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 102. Average June potential evapotranspiration in the 

Delaware River basin.
POTENTIAL EVAPOTRANSPIRATION1 105

EXPLANATION

Potential evapotrans- 

-= =-- jn inches

'" ' l-Py^ \t^&* ^tf-ON

^XO ^ ' T \ x 1-^C' ^ i

/

l,r-j-^ UVJWIKJ

'*^|H°°><

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

Y/"4-'v R/! f ' FIGURE 103. ^Average July potential evapotranspiration in the

Delaware River basin.
106 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASIN

v -"£-,

\ "(Schphaf te !

VSL ' '^

EXPLANATION

Potential evapotranspiration, in inches

50 MILES

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

A FIGURE 104. ^Average August potential evapotranspiration in 

the Delaware River basin.
POTENTIAL FA'APOTRAMSPI RATION 107

Potential evapotranspiration, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 105. Average September potential evapotranspiration 

in the Delaware River basin.
108 CLIMATIC ATLAS OF THE DEIAWARE RIVER BASIN

Potential evapotrans 

piration, in inches

50 MILES

-suss ^ <5S^^/v >/rr"v R'VKK FIGURE 106. Average October potential evapotranspiration in

BASE FROM U.S. GEOLOGICAL SURVEY 1 x ^, ^ \ "' fhf> n^lawarp Rivpr ha<;in UNITED STATES BASE MAP, 1970 [ __ ^ __^i the Delaware Kiver basin.
PO FENTIAL EVAPOTRANSPIRATION 109

/" > > ! / / ;% - ,.i

 -¥TS%^z r^fW . 

, fr s f'/^p&KJe

' W.lkeJeaWe 1 ,^'-4: ^7/ ^ x ! , v / , L EXPLANATION

Potential evapotrans 

piration, in inches

50 MILES

0 25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

^yv"'.l "'"'''' FIGURE 107. ^Average November potential evapotranspiration

in the Delaware River basin.
110 CLIMATIC ATLAS OF THK OKI AWARE RIYF.R BASIN

WATER SURPLUS

The largest water surpluses of over 26 in. are 

calculated for the Catskills stations, where temperatures 

(and potential evapotranspiration) are relatively low for 

the basin and where precipitation totals are relatively 

high. The lowest values, less than 16 in., occur in the 

southern part of the basin. The extreme northwestern 

area of the basin is associated with relatively low water 

surpluses (18 to 22 in.) due to relatively low precipitation receipt.

The water surpluses occur seasonally; the winter 

months are the times of high surplus (figs. 109-117). 

Figures 111, 113,115, and 117 depict the average water 

surplus over the basin for winter, spring, summer, and 

fall, respectively. Time series plots (figs. 110, 112, 114, 

and 116) for four stations along a north-south transect 

within the basin accompany the maps. Water surpluses 

dominate the winter and spring seasons. Average 

surplus values for summer are the result of a few individual years of water surplus being averaged with 

many years of no summer water surplus. In the fall, 

situations of water surplus are more common than in 

summer but some years of zero surplus have occurred.

FIGURE 108. Early morning fog passing through the Delaware River gap, resulting from the condensation of water in a 

cold air mass that descended into the valley during a clear, calm night.
EXPLANATION

Water surplus, in inches

Ill

< 

50 MILES

I

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

UNITED STATES BASE MAP, 1970 t ^

FIGURE 109. Areal distribution of average annual water 

surplus in the Delaware River basin.
112 CLIMATIC; ATI AS OF THE DEI AW ARE RIVER BASIN

20

15 

10

5 

n

- HAWLEY, PA.

-

-

pi r-| rn |

-

-

20

INCHES 

01o 

5 

n

- INDIAN MILLS, N.J.

-

-

 |

-.

 . rn r-i

rn

-

rn

-i

-

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

10

BELVIDERE, N.J.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

o 10

z:

GEORGETOWN, DEL.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 110. Average water surplus during winter (December-February) at four stations in the Delaware River basin.
WAlKRSl'RPI.rS 113

EXPLANATION

Water surplus, in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

lf'v'r ! " FIGURE 111. Areal distribution of average water surplus during 

winter (December-February) in the Delaware River basin.
114 CLIMATIC. ATLAS OF THK DEI AWARE RIVER BASIN

20

15

10

5

n

- HAWLEY, PA.

-

-

 |

-

^

-i

"

-

J

 | _

-

-

 |

1

 I

- -

20

15

U)

LU

gio

5

n

- INDIAN MILLS, N.J.

-

! !

~

-

 

 

-

-

1

. .

-

~

-

fr -

-i P

_P -

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

BELVIDERE, N.J.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

20

o 10

GEORGETOWN, DEL.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 112. Average water surplus during spring (March-May) at four stations in the Delaware River basin, 1950-79.
WAFER SURPLUS 115

EXPLANATION

Water surplus in inches

50 MILES

50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

FIGURE 113. Areal distribution of average water surplus during

cndno- spring fMnt-rh viarcn-Maj Mnvl inin
116 CLIMATIC ATI AS OF 1 HE DEI AWARE RIVER BASIN

HAWLEY, PA.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

INDIAN MILLS, N.J.

-TIMI n

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

15

10

BELVIDERE, N.J.

r-n n 50 52 54 56 58 60 62 64 i 

YEARS

70 72 74 76 78

O 10

GEORGETOWN, DEL.

1

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 114. Average water surplus during summer Qune-August) at four stations in the Delaware River basin 1950-79.
WATER SURPLUS 117

EXPLANATION

Water surplus, in inches

*-t ' v-"-" Sctoq teti

!EjktoriK£ ^ .,. -^ %l \ / \X ."" ,jj

°i^ ci! « ;SALE^ " vfo ^F.W JE8$ Y ^5 ' f/^p^xY^ 

..'^IHmC,^1 ^1^ - 

**^kW

%«SyS \^S?

l FIGURE HS.^Areal distribution of average water surplus during

ciimm^r summer riiin^ une-Auust AiifTiicn inin

50 MILES

J

50 KILOMETERS

UNITED STATES BASE MAP, 1970 t _
118 CLIMATIC ATLAS OF THE DELAWARE RIVER BASIN

20

10

HAWLEY, PA.

n

20

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

INDIAN MILLS, N.J.

-rfH

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

20

BELVIDERE, N.J.

20

O 10

GEORGETOWN, DEL.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 116. Average water surplus during fall (September-November) at four stations in the Delaware River basin, 1950-79.
WATER SURPLUS 119

EXPLAIMATIOIM

Water surplus, in inches

50 MILES

50 KILOMETERS

UNITED STATES BASE MAP, 1970

v'^'" FIGURE 117. Areal distribution of average water surplus during M (September-November) in the Delaware River basin.
120 CLIMATIC ATLAS OF THE DEI AWARE RIVER BASIN

WATER DEFICIT

Periods of water deficit are concentrated during the 

summer months when potential evapotranspiration 

values are maximum (figs. 118 and 119). The map of 

average annual water deficit (fig. 119) indicates deficits 

of 4 in. in the southern part of the Delaware River basin 

and values of less than 2 in. in the north, where the annual climatic water demand is less.

The drought years in the early 1950's and the 

mid-1960's appear in the time series plots of annual 

water deficit (fig. 118).

DROUGHT

Drought may be defined in many ways. Perhaps the 

most commonly used definition relates drought to 

agricultural activities; drought occurs when precipitation is insufficient to provide for the water needs of 

plants. When considering drought within the Delaware

River basin, this definition must be expanded upon 

because agriculture is but one of the many activities that 

place a demand on the water supply of this highly 

populated region. A series of reservoirs have been constructed within the basin to store water surpluses that 

occur typically during the winter half of the year. These 

reservoirs serve to ensure water availability throughout 

the year for industrial and domestic purposes and for 

agricultural irrigation. Thus, winter precipitation is of 

critical importance to the water supply of the region, as 

is that of the summer growing season.

The Delaware River basin has been significantly affected by drought during three episodes since 1950. The 

1952-55 period was characterized by unusually high 

summer temperatures over the entire country with 

relatively low precipitation totals. Namias (1955) related 

this to the extension of the Bermuda subtropical high 

pressure system across the Southern United States. This 

resulted in anomalous easterly and northeasterly flow

HAWLEY, PA.

50 52 54 56 58 60 62 64 66 68 70 72 74 

YEARS

76 78

INDIAN MILLS, NJ.

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

- BELVIDERE, N.J.

. !

, ,

_

i

-

-

qj Til

 

-

 |

12

11

-, 10

-

-

-

_

-

^^

9

8

7

C/3

LJJ c 

X

4

3

2 

1

n

GEORGETOWN, DEL.

-

-

-

-

-

, ,

-

T- T

, I

 

 T

j I

. .

-

-

-

-

-

_

-

-

- -

-

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

YEARS

FIGURE 118. Average annual water deficit at four stations in the Delaware River basin, 1950-79.
DROUGHT 121

EXPLANATION

Water deficit, in inches

50 MILES

50 KILOMETERS

UNITED STATES BASE MAP, 1970

».v KJ\ EH pIGURE iig Areal distribution of average annual water deficit 

in the Delaware River basin.
122 CLIMATIC: ATLAS OF THE DEI AWARE IWER BASIN

components in the Gulf of Mexico area, which inhibited 

the flow of moist gulf air into the Northeast. Figures 

120A and 120B show the annual water deficits (Thornthwaite method) for the Delaware River basin for the 

years 1953 and 1954, respectively. These may be compared with the average annual water deficits shown in 

figure 119.

A drought that was much less extensive than that of 

the early 1950's was felt primarily in the Northeastern 

United States including the Delaware River basin. This 

drought began in the summer of 1961, became severe 

in the fall of 1963, and lasted through the summer of 

1965 (Andrews, 1966). Namias (1966) attributes the dry 

conditions in the Northeast during this period to an 

eastward displacement of the trough off the Atlantic 

Coast and an accompanying shift of the major storm 

tracks. Figure 120C shows the annual water deficits for 

1964 as a representative example of conditions associated with this drought period.

The third drought affecting the Delaware River basin 

since 1950 began to develop in May 1980, when the 

Northeast was downstream from a major ridge that extended from western Canada into the North-Central 

United States. This resulted in relatively low precipitation amounts for the month, particularly in the northern 

parts of the Delaware River basin (Taubensee, 1980a). 

During June and July, an amplified circulation 

developed having strong ridges at the 700-millibar level 

over the central Pacific, Central United States, and central Atlantic; troughs were situated near each coast. Subtropical highs extended over much of the southern part

of the country. This marked the beginning of the heat 

wave and drought conditions that charcterized the summer of 1980 for most of the United States east of the 

Rockies (Livezey, 1980; Dickson, 1980). The full impact 

of the 1980 drought was felt within the Delaware River 

basin during August, when the 700-millibar high 

pressure center shifted eastward. The Northeast experienced high temperatures, and precipitation within 

the Delaware River basin was generally less than half 

of average amounts. Philadelphia's average temperature 

of 80 °F for the month was the highest for August since 

1900. Allentown's rainfall of 0.93 in. was the lowest for 

August since recordkeeping began in 1923 (Wagner, 

1980). During September, anomalously high pressure remained in the southeastern part of the country, and 

drought conditions continued in the Delaware River 

basin, particularly in the northern parts (Taubensee, 

1980b). Precipitation totals during October and 

November were closer to average values but still lower 

than normal (Dickson, 1981; Livezey, 1981). December 

conditions were devastating to the water supply situation of the Delaware River basin. Low precipitation 

amounts were the result of strong northwesterly flow 

that prevented gulf moisture from reaching the area. 

Much of the region received less than 25 percent of normal precipitation. Trenton, N.J., experienced the second 

driest December on record with a total precipitation of 

only 0.58 in. (Taubensee, 1981). Figure 120D shows the 

1980 cumulative water deficit, as calculated by the 

Thornthwaite method described earlier, for selected stations in the Delaware River basin.
DROUGHT

76' 75

76

EXPLANATION

Water deficit, in inches

10.0 

8.0 

6.0 

4.0 

2.0

39 C

0 25 50 MILES I ,., . . . i i

0 25 50 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

UNITED STATES BASE MAP, 1970

D

FIGURE 120. Annual water deficits in the Delaware River basin during A 1953; B, 1954; C, 1964; and D, 1980.
124 CLIMATIC ATI AS OF THE DEI AWARE RIVER BASINHURRICANES AND TROPICAL STORMS

The Delaware River basin is not within the major 

North Atlantic hurricane belt. Storms of tropical origin 

have entered the area, but in most cases they have 

traveled parallel to the coast, either on land or on sea, 

and the full intensity of the storm has not been felt 

within the region. Nevertheless, considerable damage 

has been attributed to these tropical storms.

By convention, tropical cyclones having maximum 

wind speeds of at least 39 mph but less than 74 mph are 

known as tropical storms; those with winds of at least 

74 mph are hurricanes. On the average, four tropical 

cyclones per year reach the mainland United States; two 

of these, on the average, reach hurricane strength. These 

systems originate in tropical latitudes, often as easterly 

waves, move westward, and then recurve toward the 

north or northeast. The systems move at 10 to 20 mph 

during formation and at speeds of 40 mph or more when 

fully developed (Baldwin, 1973; Dunn and Miller, 1960).

Dunn (1951) has recognized four major stages in the 

life of a typical hurricane. These are (1) the formative 

stage, which includes the development of the storm to 

the point where winds of hurricane strength occur; (2) 

the stage of immaturity, when the cyclone remains compact while the pressure gradient increases; (3) the 

mature stage, during which the cyclone expands in area; 

and (4) the decaying stage marked by landfall and dissipation or by northward movement and acquisition of 

extratropical characteristics.

In an average-sized hurricane, the diameter of 

hurricane-force winds is 100 mi; winds of gale force cover 

a 350-400 mi diameter, but great variability exists. The 

eye of the hurricane, which is an area of light winds, 

clear sky, and relatively warm temperatures, averages 

14 mi in diameter but has been known to range from 

4 to 25 mi across. Maximum wind speeds recorded at 

land stations during hurricanes exceeded 150 mph 

(Dunn and Miller, 1960).

Destruction associated with tropical cyclones occurs as 

a result of strong winds, storm tides, and heavy rainfall. 

Heavy rains and accompanying flooding have been the 

primary causes of tropical cyclone-related damage within 

the Delaware River basin.

Figure 121 shows the paths of hurricanes and tropical 

storms of the 1950-79 period that have affected parts 

of the Delaware River basin. Brief descriptions of the individual systems follow.

Hurricane Carol (August 26-31,1954) passed offshore 

in the Delaware River basin latitudes but did major 

damage in the Carolinas and in New England. The 

Delaware River basin was affected by heavy precipitation and strong winds but escaped the major destruction 

experienced by the areas to the north and south 

(Winston, 1954; Davis, 1954).

Hurricane Edna (September 6-11, 1954) followed a 

path similar to that of Carol. The area of strong winds 

and heavy rainfall extended into the Delaware River 

basin, but again the area escaped the major damage of 

the storm (Malkin and Holzworth, 1954; Davis, 1954).

Hurricane Hazel (October 5-16, 1954) reached the 

South Carolina coast on October 15 and maintained 

unusually strong winds as it moved northward. The path 

was west of the Delaware River basin, but the entire 

region suffered extensive damage as a result of strong 

winds and heavy rains (Krueger, 1954; Davis, 1954).

Hurricane Connie (August 3-13, 1955) reached the 

North Carolina coast on August 12 and moved toward 

the Washington, D.C., area and into Pennsylvania. Dry 

weather preceded Connie, so the heavy rainfall associated with the storm did little damage and served to 

replenish the soil-moisture supply in affected areas (Gentry, 1956).

Hurricane Diane (August 10-19,1955) followed closely 

on the heels of Connie, reaching the North Carolina coast 

August 17. It then moved northward and eastward, affecting areas that had recently experienced the passage 

of Hurricane Connie. Namias and Dunn (1955) attribute 

the unusual occurrence of "twin" hurricanes to an abnormally contracted circumpolar vortex. Although 

Diane was not a particularly intense storm, the torrential rains that fell from eastern Maryland to 

southeastern New England resulted in major flooding 

of many streams, including the Delaware River and its 

tributaries. Resulting property damage earned Diane the 

nickname "the Billion Dollar Hurricane" (Gentry, 1956; 

Dunn and Miller, 1960).

Tropical Storm Brenda (July 28-31, 1960) moved into 

western Florida on July 28 and traveled along the Atlantic Coast. The major effect of the storm in the Delaware 

River basin was heavy rain (Moore, 1961).

Hurricane Donna (August 29-September 13, 1960) 

reached Florida on September 10 and moved northward 

along the Atlantic Coast. The storm was associated with 

gale-force wind extending inland, heavy precipitation, 

and extensive property damage (McGuire, 1960; Tisdale, 

1960).

Tropical Storm Doria (August 20-29, 1971) reached the 

North Carolina coast on August 27 and moved along the 

Atlantic Coast to New England. Flooding was the major cause of damage (Pardue and Hope, 1972).

Hurricane Agnes (June 14-22, 1972) entered the 

Florida panhandle on June 19. It intensified when it 

merged with a major extratropical storm. On June 21 

a secondary low developed west of the original center, 

and two lows moved northward. The system intensified 

to reach tropical storm status again over North Carolina. 

The lowest pressure recorded for Agnes was 977 

millibars just off the New Jersey coast. Precipitation 

totals for the storm were in the 10 to 14 in. range in
HURRICANES AND TROPICAL STORMS 125

EXPLANATION

Hurricanes and tropical storms affecting 

the Delaware River basin 1950 - 1979

 Carol (H) Aug. 25-31, 1954 

 Edna (H) Sept. 2-14, 1954

 - Hazel (H) Oct. 5-18, 1954

 Connie (H) Aug. 3-14, 1955

 Diane (H) Aug. 7-21, 1955

 Brenda(T)July 28-31, 1960

 Donna (H) Aug.29-Sept. 13, 1960 

Doria(T) Aug. 20-29, 1971

 - Agnes (H) June 14-22, 1972

Belle (H) Aug. 6-10, 1976 

(H) Denotes hurricanes 

(T) Denotes tropical storms

30

15'

FIGURE 121. Path of hurricanes and tropical storms that affected the Delaware River basin, 1950-79.
126 CLIMATIC ATI AS OF THE DKI AWARE RIVT.R BASIN

eastern Pennsylvania. These rains fell on saturated soil, 

so that most of the damage of the storm was due to river 

flooding. Agnes was one of the largest June hurricanes 

of record, with a circulation diameter of 1,000 nautical 

miles. It was also the most costly United States storm 

with respect to dollar damages (Simpson and Hebert, 

1973).

Hurricane Belle (August 6-10,1976) moved over water 

parallel to the Atlantic Coast until making landfall on 

Long Island on August 10 The storm rainfall within the 

Delaware River basin was generally less than 2 in., and 

most damage was related to strong winds (Lawrence, 

1977).

SELECTED REFERENCES

Andrews, J.F., 1966, The circulation and weather of 1965: Weatherwise, v. 19, p. 5-11, 23.

___.1968, The weather and circulation of August 1968 

Sharp contrasts in temperature and an unusually strong summer index cycle: Monthly Weather Review, v. 96, p. 826-832.

___ 1969, The weather and circulation of July 1969 

A predominantly wet month, cool in the North and warm in the 

South: Monthly Weather Review, v. 97, p. 735-738.

Baldwin, J.L., 1973, Climates of the United States: Washington, B.C., 

U.S. Government Printing Office, 113 p.

Brinkmann, W.A.R., 1976, Surface temperature trend for the Northern 

Hemisphere Updated: Quaternary Research, v 6, p. 355-358.

___ 1979, Associations between temperature trends: Annals, 

Association of American Geographers, v. 69, p. 250-261.

Bryson, R.A., and Murray, T.J., 1977, Climates of hunger: Mankind 

and the world's changing weather: Madison, University of Wisconsin Press, 171 p.

Davis, W.R., 1954, Hurricanes of 1954: Monthly Weather Review, 

v. 82, p. 370-373.

Dickson, R.R., 1964, The weather and circulation of June 1964 A reversal of a long-standing trend over the Pacific: Monthly Weather 

Review, v. 92, p. 428-432.

___ 1965, The weather and circulation of November 1964 

Contrasting weather regimes related to long-wave progression: 

Monthly Weather Review, v. 93, p. 123-126.

___.1966, The weather and circulation of December 1965 

Including a discussion of the record dry year in the Northeast: 

Monthly Weather Review, v. 94, p. 192-197.

___1973, Weather and circulation of November 1972 Another 

cold, wet month: Monthly Weather Review, v. 101, p . 182-186.

___1977, Weather and circulation of November 1976 Record cold 

over the South and Midwest for the second consecutive month: 

Monthly weather review, v. 105, p. 239-244.

___1980, Weather and circulation of June 1980 Inception of a heat wave and drought over the central and south Great 

Plains: Monthly Weather Review, v. 108, p. 1,469-1,474.

___1981, Weather and circulation of October 1980 A decisive

end to the heat wave: Monthly Weather Review, v. 109,

p. 205-211. 

Dunn, C.R., 1960, The weather and circulation of March 1960 A cold,

snowy month: Monthly Weather Review, v. 88, p. 112-120. 

Dunn, G.E., 1951, Tropical cyclones, in Compendium of meteorology:

Boston, Mass., American Meteorological Society, p. 887-901. 

Dunn, G.E., and Miller, B.I., 1960, Atlantic hurricanes: Baton Rouge,

Louisiana State University Press, 326 p.

Gentry, R.C., 1956, The 1955 hurricane season: Weatherwise, v. 9,

p. 11-13, 29-31. 

Green, R.A., 1964, The weather and circulation of October

1963 Abnormal warmth and severe drought in the United States

and two unusual hurricanes offshore: Monthly Weather Review,

v. 92, p. 37-42. 

Harkness, WE., Lins, H.F., and Alley, W.M., 1986, Drought in the

Delaware River basin, 1984-85, in National Water Summary

1985 Hydrologic Events and Surface-Water Resources, U.S.

Geological Survey Water-Supply Paper 2300, p. 29-34. 

Harmon, J.R., 1971, Tropospheric waves, jet streams, and United States

weather patterns: Washington, D.C., Association of American

Geographers, 37 p. 

Krueger, A.F., 1954, The weather and circulation of October

1954 Including a discussion of Hurricane Hazel in relation to

the large-scale circulation: Monthly Weather Review, v. 82,

p. 296-300. 

Lawrence, M.B., 1977, Atlantic hurricane season of 1976: Monthly

Weather Review, v. 105, p. 497-507. 

Livezey, R.E., 1980, Weather and circulation of July 1980 Climax of

a historic heat wave and drought over the United States: Monthly

Weather Review, v. 108, p. 1,708-1,716. 

__ JL981, Weather and circulation of November 1980 A late

heat wave and hurricane and early snow: Monthly Weather

Review, v. 109, p. 396-402. 

Malkin, W, and Holzworth, G.C., 1954, Hurricane Edna, 1954: Monthly

Weather Review, v. 82, p. 267-279. 

Mather, J.R., 1978, The climatic water budget in environmental

analysis: Lexington, Mass., Lexington Books, 239 p. 

McGuire, J.K., 1960, Hurricane Donna in the Northeast: Weatherwise,

v. 13, p. 215-217. 

Moore, PL., 1961, The hurricane season of 1960: Weatherwise, v. 14,

p. 18-23. 

Namias, J., 1955, Some meteorological aspects of drought With special

reference to the summers of 1952-54 over the United States:

Monthly Weather Review, v. 83, p. 199-205. 

___1966, Nature and possible causes of the northeastern

United States drought during 1962-65: Monthly Weather Review,

v. 94, p. 543-554. 

___ 1974, Longevity of a coupled air-sea-continent system:

Monthly Weather Review, v. 102, p. 638-648.

Namias, J., and Dunn, C.R., 1955, The weather and circulation of 

August 1955 Including the climatological background for Hurricanes Connie and Diane: Monthly Weather Review, v. 83, 

p. 163-170.

Neumann, C.J., Cry, G.W, Case, E.L., and Jarvinen, B.R., 1978, Tropical 

cyclones of the North Atlantic Ocean, 1871-1977: Washington, 

D.C., U.S. Government Printing Office.

Pardue, L.G., and Hope, J.R., 1972, The hurricane season of 1971: 

Weatherwise, v. 25, p. 11-19.

Reitan, C.H., 1974, A climatic model of solar radiation and temperature 

change: Quaternary Research, v. 4, p. 25-38.

Simpson, R.H., and Hebert, P.J., 1973, Atlantic hurricane season of 

1972: Monthly Weather Review, v. 101, p. 323-333.

Stark, L.P., 1967, The weather and circulation of May 1967 Strong 

blocking and record cold in the East: Monthly Weather Review, 

v. 95, p. 587-592.

Taubensee, R.E., 1970, The weather and circulation of September 

1970 Warm in the East and cool in the West with heavy precipitation in many central areas: Monthly Weather Review, v. 98, 

p. 939-943.

___1974, Weather and circulation of December 1973 A wet 

month over much of the country: Monthly Weather Review, 

v. 102, p. 262-267.
SELECTED REFERENCES 127

_1977, Weather and circulation of March 1977 Record 

and near-record precipitation eases drought in parts of the Great 

Plains and Midwest: Monthly Weather Review, v. 105, p. 793-799.

_1980a, Weather and circulation of May 1980 Record 

heavy precipitation in the northern Rocky Mountains while 

drought affected the northern Great Plains: Monthly Weather 

Review, v. 108, p. 1,270-1,277.

_1980b, Weather and circulation of September 1980 Heat wave 

ends late in the month: Monthly Weather Review, v. 108, 

p. 2,100-2,106. 

_1981, Weather and circulation of December 1980 A generally

dry month with record warmth in the West: Monthly Weather 

Review, v. 109, p. 676-682.

Thornthwaite, C.W, 1948, An approach toward a rational classification of climate: Geographical Review, v. 38, p. 55-94.

Tisdale, C.F., 1960, The weather and circulation of September 

1960 Including a discussion of tropical storm activity: Monthly 

Weather Review, v. 88, p. 353-361.

U.S. Council on Environmental Quality, 1975, The Delaware River 

basin: An environmental assessment of three centuries of change: 

Washington, D.C., US. Government Printing Office, 87 p.

U.S. National Oceanic and Atmospheric Administration, 1950-1980, 

Climatological data, annual and monthly summaries for Maryland and Delaware, New Jersey, Pennsylvania, and New York: 

Washington, D.C., U.S. Government Printing Office. 

^1960-1979, Climatological data, national summary, annual 

and monthly summaries: Washington, DC., U.S. Government 

Printing Office. 

.1977, Daily weather maps, weekly series, January 17-23,1977:

Washington, DC., U.S. Government Printing Office. 

Wagner, A.J., 1977a, Weather and circulation of January 1977 The

coldest month on record in the Ohio Valley: Monthly Weather

Review, v. 105, p. 553-560. 

___1977b, Weather and circulation of April 1977 Generally

mild and wet but continued drought in the West: Monthly Weather

Review, v. 105, p. 933-939. 

___1978, Weather and circulation of January 1978 Cold with

record snowfall in the Midwest and Northeast, mild and wet in

the West: Monthly Weather Review, v. 106, p. 579-585. 

___1980, Weather and circulation of August 1980 Eastward

spread of heat wave and drought: Monthly Weather Review, 

v. 108, p. 1,924-1,932.

Winston, J.S., 1954, The weather and circulation of August 

1954 Including a discussion of Hurricane Carol in relation to 

the planetary wave pattern: Monthly Weather Review, v. 82, 

p. 228-236.

SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports 

of wide and lasting interest and importance to professional scientists 

and engineers. Included are reports on the results of resource studies 

and of topographic, hydrologic, and geologic investigations. They also 

include collections of related papers addressing different aspects of a 

single scientific topic.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resource studies and of geologic and topographic investigations, as 

well as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of wide 

interest to professional geologists, hydrologists, and engineers. The 

series covers investigations in all phases of hydrology, including 

hydrogeology, availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for 

distribution at no cost to the public. Information is usually of short-term 

interest.

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the formal 

USGS publications series. Copies are reproduced on request unlike 

formal USGS publications, and they are also available for public 

inspection at depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, 

maps, and other material that are made available for public consultation 

at depositories. They are a nonpermanent form of publication that may 

be cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 7.5- or 15-minute quadrangle formats (scales 

mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include 

structure and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric bases at various scales; they show results of surveys using 

geophysical techniques, such as gravity, magnetic, seismic, or radioactivity, which reflect subsurface structures that are of economic or 

geologic significance. Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also 

includes 7.5-minute quadrangle photogeologic maps on planimetric 

bases that show geology as interpreted from aerial photographs. Series 

also includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial 

geology, stratigraphy, and structural relations in certain coal-resource 

areas.

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum 

potential.

Miscellaneous Field Studies Maps are multicolor or blackand-white maps on topographic or planimetric bases on quadrangle or 

irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or blackand-white maps on topographic or planimetric bases presenting a wide 

range of geohydrologic data of both regular and irregular areas; 

principal scale is 1:24,000, and regional studies are at 1:250,000 scale 

or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, 

Books and Open-File Reports Section, Federal Center, Box 25425, 

Denver, CO 80225. (See latest Price and Availability List.)

"Publications of the Geological Survey, 1879-1961" may be 

purchased by mail and over the counter in paperback book form and as 

a set of microfiche.

"Publications of the Geological Survey, 1962-1970" may be 

purchased by mail and over the counter in paperback book form and as 

a set of microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" may 

be purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased by 

mail and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by 

mail and over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback 

booklet form only.

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" are available free of charge by mail or may 

be obtained over the counter in paperback booklet form only. Those 

wishing a free subscription to the monthly catalog "New Publications of 

the U.S. Geological Survey" should write to the U.S. Geological 

Survey,-582 National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, announcements, and publications may be incorrect. Therefore, 

the prices charged may differ from the prices in catalogs, announcements, and publications.