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Climatic Features and Length of Growing Season in Alabama

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BULLETIN 517 MAY 1980 NOAA/NATIONAL WEATHER SERVICE AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY R.DENNIS ROUSE, DIRECTOR AUBUR' N,ALABAMA

CONTENTS
............................................ INTRODUCTION SOURCE OF DATA AND ANALYSIS ................................ THE GROWING SEASON ....................................... PROBABLE LENGTHS OF GROWING SEASON ...................... CLIMATIC FEATURES ......................................... ............................................... SUMMARY BIBLIOGRAPHY ............................................ APPENDIX ...................................................

Page 3 4 6
13 14

21
22

23

TABLES
1.
STATION LOCATION AND ELEVATION ..........................

5

2. 3.

AVERAGE DATES OF THE LAST FREEZE IN THE SPRING, FIRST FREEZE IN THE FALL, AND AVERAGE NUMBER OF GROWING SEASON DAYS ............................................ STATION INDEX TO PROBABLE LENGTHS OF GROWING SEASON ....

8
23

FIGURES
1.
LOCATIONS OF

73

TEMPERATURE REPORTING STATIONS USED

IN GROWING SEASON ANALYSIS ..............................

7
10 11 12

2. AVERAGE LENGTH OF GROWING SEASON (DAYS) .............. 3. MEAN DATE OF FIRST 32°F FREEZE IN THE FALL ............. 4. MEAN DATE OF LAST 32°F FREEZE IN THE SPRING ............ 5. CLIMATIC FEATURES BASED ON GEOGRAPHIC VARIATIONS IN
NORMAL LENGTH OF GROWING SEASON ...................... TOPOGRAPHY OF ALABAMA................................ 7. PHYSIOGRAPHIC REGIONS AND MAJOR RIVERS WITHIN ALABAMA..

6.

15 16
17

FIRST PRINTING

3M,

MAY 1980

Information contained herein is available to all persons without regard to race, color, sex, or national origin.

CLIMATIC FEATURES and LENGTH of GROWING SEASON in ALABAMA
JERE R. GALLUP*

INTRODUCTION

THE CLIMATIC INTERVAL during which meteorological conditions permit plant growth is called the growing season. A particular area's geography or climatic classification determines what limitations to plant growth will apply. Usually, temperatures and the amount of dryness are the greatest constraints to growing season. In temperate climates like Alabama's, annual changes of temperature clearly define the seasons during which plant growth processes can take place. Temperature restrictions to growing season can be closely fixed to freezing (32°F), although other temperature levels become important as well in determining the active growing season. Besides temperature ranges that may affect growing season, the availability of moisture can be an important influence on seasonal growth patterns. This is most apparent in agriculturally dry areas of the world or where monsoon climates regulate farming practices according to a marked wet and dry season. Since variations of moisture are of less significance to growing season in Alabama, this publication deals only with the temperature factor. The agricultural growing season is usually interpreted according to the particular crop that is being produced. The farmer with row crops needs to know how to best schedule the planting and harvest operations during the year. Fruit growers time their activities from the first break in dormancy up until picking time. Livestock producers measure growing season as the time of year
'Agricultural Meteorologist, NOAA, National Weather Service, Environmental Studies Service Center, Auburn University, Alabama 36849.

4

ALABAMA AGRICULTURAL EXPERIMENT STATION

when pastures are green and alive. When selecting among different crop varieties, there is usually a need for the farmer to base at least part of the decision on climatic factors such as growing season. Predictions of crop size and quality, as well as seasonal variations in the supply of produce, all depend upon the type of growing season. Understanding the effects of weather and climate on growing season, therefore, is necessary when resolving the economic uncertainties of food and fiber production. Besides agriculture, the growing season affects many other areas of commerce such as transportation and storage of agricultural commodities, availability and need for seasonal labor, and general market conditions. Knowledge of climate that affects the operations of a farm or any weather sensitive business is important when evaluating long-term plans and decisions. This use of climatology helps avoid purely subjective appraisals about weather beyond a period in which day-to-day changes or trends for the immediate term are more evident. This publication's purpose is to provide an interpretation of growing season within Alabama as well as point out and describe some of the State's climatic features.

SOURCE OF DATA AND ANALYSIS The data concerning growing season analysis were extracted from the Alabama Climatological Data minimum temperature records for the past 20-to 35- years ending in 1978. Table 1 lists the localities selected for analysis along with their respective lengths of meteorological record. A base map that follows in figure 1 can be used to identify the approximate location of each of the numbered stations. From these data the average dates of last freeze in the spring, the average dates of first freeze in the fall, and the average length of growing season were calculated. Table 2 summarizes this information. From the analyzed data, maps were drawn to give a visual description of growing season across the State. Isopleths in figure 2 represent the length of average annual growing season in days. For the beginning and end to growing season, average dates are pictured in the analysis of figures 3 and 4. Probable lengths of growing season were also computed for each station based on consecutive years of historical growing season. These are portrayed in the graphs in the Appendix.

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON
TABLE 1. STATION LOCATION AND ELEVATION

5

Station 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. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. '(I

County

Albertville...........Marshall Andalusia...........Covington Anniston............Calhoun Ashland.............Clay Athens..............Limestone Auburn.............Lee Tuscaloosa Bankhead L&D. Bay Minette.........Baldwin Belle Mina...........Limestone Bessemer...........Jefferson Birmingham.........Jefferson Brantley............Crenshaw Brewton............Escambia Bridgeport..........Jackson Calera..............Shelby Camp Hill..........Tallapoosa Centre.............Cherokee Centreville..........Bibb hatom.............Washington Childersburg.........Talladega Clanton.............Chilton Clayton.............Barbour Coden..............Mobile Dayton............Marengo Marengo Demopolis L&D. Winston Double Springs. Fairhope............Baldwin Falkville............Morgan Fayette.............Fayette Florence............Lauderdale Monroe Frisco City .......... Etowah Gadsden ............ Geneva Geneva ............. Hale Greensboro .......... Butler Greenville ........... Guntersville.......... Marshall Winston Haleyville ........... Marion Hamilton ............ Henry Headland ........... Cleburne Heflin .............. Highland Home..Crenshaw Chambers Lafayette ........... Sumter Livingston ........... Madison Madison ............ Marion Junction..Dallas Elmore Martin Dam ......... Dallas Minter .............. Mobile Mobile.............. Montgomery......... Montgomery Lawrence Moulton ............ Muscle Shoals........ Colbert Oneonta............ Blount

Latitude Longitude Elevation Deg. Mi Deg. Mn. Ft. 1,140 34 14 86 10 31 19 86 30 242 611 33 35 85 51 33 15 85 50 1,091 720 34 48 86 59 652 32 37 85. 29 280 33 27 87 21 268 30 53 87 47 600 34 42 86 53 33 22 87 01 540 620 33 34 86 45

31

35

86

16

274

31 34 33 32 34 32 31 33 32 31 30 32 32 34 30 34 33 34 31 34 31 32 31 34 34 34 31 33 31 32 32 34 32 32 32 30 32 34 34 33 [~I

04 57 05 50 07 54 32 17 51 53 23 22 31 10 33 22 41 48 26 02 02 42 49 20 15 06 21 39 57 54 35 42 28 40 06 41 18 29 45 57 %~i

87 85 86 85 85 87 88 86 86 85 88 87 87 87 87 86 87 87 87 86 85 87 86 86 87 87 85 85 86 85 88 86 87 85 87 88 86 87 87 86

03 43 47 39 44 15 15 20 38 28 14 39 50 24 53 53 49 41 24 00 51 35 38 19 37 59 20 36 19 24 12 45 13 55 03 15 24 18 37 29

85 615 540 680 620 456 285 418 580 596 12 230 100 800 23 625 365 578 410 565 110 220 445 578 950 435 370 850 594 830 160 580 200 340 370 211 221 645 540 870

record Yrs. 26 28 28 22 24 28 22 31 28 25 28 23 31 25 24 26 23 31 28 22 28 23 23 28 28 22 38 23 28 25 28 28 31 28 31 25 31 22 28 23 28 31 28 29 29 28 22 28 28 22 31 31 Continued

6

ALABAMA AGRICULTURAL EXPERIMENT STATION
TABLE 1 (Continued). STATION LOCATION AND ELEVATION

Station 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. Ozark .............. Prattville ............ Red Bay ............ Redstone Arsenal .... Robertsdale ......... Rockford ........... Rock Mills .......... Russellville ........... Saint Bernard ........ Sand Mountain ...... Scottsboro .......... Selma ............... Sylacauga ........... Talladega ........... Thomasville ......... Troy. .............. Tuscaloosa .......... Union Springs ....... Valley Head ......... Vernon ............. Waterloo ............

County Dale Autauga Franklin Madison Baldwin Coosa Randolph Franklin Cullman DeKalb Jackson Dallas Talladega Talladega Clarke Pike Tuscaloosa Bullock DeKalb Lamar Lauderdale

Length of Latitude Longitude Elevation record Ft. Yrs. Deg. Min. Deg.Min. 470 28 31 31 85 41 27 295 32 29 86 29 22 680 34 26 88 08 23 573 34 35 86 36 31 155 30 34 87 44 25 670 32 54 86 14 31 745 09 85 18 33 25 880 34 31 87 44 802 28 34 10 86 49 28 1,195 34 17 85 58 28 615 34 41 86 03 31 147 32 25 87 00 24 490 33 12 86 12 31 555 33 26 86 05 31 405 31 55 87 44 31 580 31 49 85 59 31 169 33 14 87 37 28 460 32 06 85 43 31 1,040 34 34 85 37 23 265 33 48 88 07 20 457 34 55 88 04

THE GROWING SEASON

No clear standard for measuring an exact growing season has been established. Shelter temperatures that have reached freezing are more applicable for general use in describing growing season than subjective observations of frost damage to vegetation. Confusion often results when associating the terms of frost and freeze. Frost forms as a deposit of ice crystals on the ground or other surfaces having cooled to below 32 0 F. The process involves the conversion of water vapor in the air directly to ice crystals. Air temperatures in the surrounding environment may actually be slightly above freezing. Often there is a problem in determining whether a frost has been severe enough to end a growing season or delay its beginning. Scattered frost damage may occur near the ground even though shelter temperatures are observed several degrees above freezing. Therefore, for a frost to be widespread enough to halt a growing season, temperatures at shelter height as well as at ground level are likely to have reached freezing. The term freeze applies to air temperatures at standard measurement height (5 feet above ground) that have fallen to 32 0 F or

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

7

FIG. 1. Locations of 73 temperature reporting stations used in growing season analysis.

8

ALABAMA AGRICULTURAL EXPERIMENT STATION

TABLE 2. AVERAGE DATES OF THE LAST FREEZE IN THE SPRING, FIRST FREEZE IN THE FAIL, AND AVERAGE NUTMBER OF GROWING SEASON DAYS

Station

Av. date last freeze in the spring Apr. 3 Mar.21 Apr. 1 Apr. 4 Apr. 8 Mar.28 Mar.30 Mar. 5 4 Apr. 3 Mar.31 Mar. 29 Mar.31 Apr. 12 Apr. 10 Apr. 7 Apr. 4 Apr. 2 Mar.30 Apr. 6 Mar.31 Mar.14

Av. date first freeze in the fall Oct. 31 Nov. 9 Nov. 2 Nov. 5 Oct. 28 Nov. 6 Nov. 6 Nov.20 Oct. 30 Nov. 2 Nov. 5 Oct. 31 Oct. 29 Oct. 24 Oct. 28 Oct. 27
Oct. 28

Av. growing season

Days
Albertville.................. Andalusia.................. Anniston................... Ashland.................... Athens..................... Auburn.................... Bankhead L&D............. Ba'-Minette................ Belle Mina...................Apr. Bessemer................... Birmingham ................ Brantley................... Brewton.................... Bridgeport.................. Calera..................... Camp Hill .................. Centre ...................... Centreville................. Chatom .................... Childersburg............... Clanton .................... Clayton ................... 211 233 215 215 203 223 221 260 209 213 219 216 212 195 201 203 207 215 221 206 214 245 258 231 232 204 270 201 203 201 239 207 234 232 242 217 203 188 249 186 238 219 216 206 226 232 241 271 242 203 221 200 247 232 217

Nov. 3
Nov. 6

Coen.....................

Mar. 5

Oct. 29 Oct. 31 Nov.14

Nov.18
Nov. 6 Nov. 6 Oct. 30 24 Nov. Oct. 27 Oct. 27 Oct. 24 1 Nov. 1 Oct. 31 Nov. 8 Nov. 14 9 Nov.. Nov. 5 Oct. 29
Oct. 21 12

Dayton ..................... Demopolis L&D ... Double Springs.............. Fairhope ................... Falkville ................... Fayette.................... Florence.................... Frisco City................. Gadsden..................... Geneva...................... Greenshoro.................. Greenville............ ...... Guntersville.................. Haleyville...................
Hamilton....................

Mar.20 Mar. 19 Apr. 9 Feb. 27 Apr. 9 Apr. 7 Apr. 6 Mar. 17 Apr. 7 Mar. 19 Mar. 22 Mar. -17 Apr. 2 Apr. 9
Apr. 16

Headland....................
Heflin .......................

Mar. 8
Apr. 18 Mar.18

Highland Home..............
Lafayette.................... Livingston................... Madison.....................
Marion

.

Nov.

Oct. 21 1 Nov."

Martin Dam................. Minter...................... Mobile...................... Montgomery.................
Moulton.................

junction..............

Mar. 30 Mar. 30 Apr. 7 Mar. Mar. 16 Feb. 28 Mar. 12
Mar. 2 6
22

Nov. 4 Nov. 1 Oct. 30
Nov. 1 3 3

Ar

Nov. 1 2 Nov. 2 6 Nov. Nov. 9
Oct. 27

7

Muscle Shoals................
Oneonta.....................

Mfar. 26
Apr. 11

Nov. 2
Oct. 26 4

Ozark........... Prattville.................... Red Bay..................... ~JU~I~1~1~11

Mar. 12 Mar. 20 Apr. 3 1IU1

Nov.' Nov. 7 Nov. 6

Continued

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

9

TABLE 2 (Continued). AVERAGE DATES OF THE LAST FREEZE IN THE SPRING, FIRST FREEZE IN THE FALL, AND AVERAGE NUMBER OF GROWING SEASON DAYS

Station Redstone Arsenal ......... Robertsdale ............. Rockford .................. Rock Mills ................. Russellville................. Saint Bernard ..............
Sand Mountain
....

Av. date last freeze in the spring Apr. 6 Mar. 8 Apr. 6 Apr. 11 Apr. 16 Apr. 11
Apr. 7

Av. date first freeze in the fall Oct. Nov Oct. Oct. Oct. Oct. 27 19 30 28 25 28

Av. growing season Days 204 256 207 200 192 200
205

.........

Oct. 29

Scottsboro................. Selma ..................... Sylacauga.................. Talladega .................. Thomasville ............. Troy ...................... Tuscaloosa ................. Union Springs ............... Valley Head ............... Vernon .................... Waterloo ................

Apr. 10 Mar.13 Apr. 8 Apr, 8 Mar. 24 Mar.18 Mar. 7 Mar.20 Apr. Apr. 13 Apr, 15

;22

Oct. 26 Nov.11 Oct. 29 Oct. 29 Nov. 8 Nov.15 Nov. 3 Nov. 9 Oct. 20 Oct. 24 Oct. 21

199 243 204 204 229 242 221 234 181 194 189

lower. A freeze may be observed with or without the occurrence of frost. For the purposes of our analysis, growing season boundaries will be determined by temperatures of 32°F or lower measured at standard height. The lines in figure 2 are of equal freeze-free period (growing season length) based on the average year. As one would expect, freezing temperatures occur both earlier in the fall and later in the spring over north Alabama. This produces a shorter growing season that averages around 200 days across the Tennessee Valley. Parts of northeast Alabama experience the shortest growing season. Southward to the Gulf Coast, the transition from colder to warmer climate occurs with a 50-to 100-day geographic variation in length of growing season. Between Huntsville and Mobile, for example, the climatic difference in growing season is about 70 days. Over interior areas of Alabama, the growing season changes most rapidly along a 30-to 50-mile wide temperature belt that spans the midsection of the State and closely parallels the northern edge of the coastal plain. Possibly because of physiographic changes in elevation along this zone, the growing season may differ by as much as 30 days over a distance of only 30 miles. Only in southwestern counties does the length of growing season change so rapidly toward the coast. The warmest climate in Alabama is found in the extreme southwestern counties. Near Mobile Bay and the Gulf Coast the yearly

10

10 ALABAMA AGRICULTURAL EXPERIMENT STATION

2 I0 \

2007

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200

,240

240.

270

IIYKYN.

5 20
0 246~2

mn
Warm

L~Cold

Centers

FIG. 2. Average length of growing season (days).

CLIMATIC

FEATURES

AND

THE

LENGTH

OF

GROWIGSASN1

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Oct.

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Oct.
25

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Nov.

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FIN

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12 __

ALABAMA AGRICULTURAL EXPERIMENT STATION

__~_____

___~_~~~_

Mar. I0

7
Mar. 15

Mar.10

Feb.

- Mar.5 SWarm Cold

FIG. 4. Mean date of last 32°F freeze in the.spring.

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

13

growing season averages almost 300 days, and the influence of a warm, marine environment is quite pronounced.
PROBABLE LENGTHS OF GROWING SEASON

Although few years lack some uniformity as to timing of seasonal change, growing seasons naturally vary in length from year to year. Periodic trends or abrupt changes in length of growing season may often occur. Certain farming practices and other activities may need to interpret the risk for such changes as they relate to an analysis of normal climate. To help accomplish this, the figures in the Appendix give probable lengths of growing season for 73 stations across Alabama. These graphs describe the probability of a growing season's length being either shorter or longer than a selected number of days. Probabilities were based on the "normal distribution" of past lengths of growing season taken from each station's climatic record. These statistics imply the assumption that the growing season climate will continue to have a character in future years similar to that described by the historical record. This assumption may hold true only for most years. Statistics could be based on prior years climatically more stable or uniform. For example, a temporary trend toward shortened growing seasons within an abnormally cold cycle of years may not be properly represented by climatological statistics. To use the graphs, a station would be selected from the index on page 23 and then referred to in the appropriate figure found in the Appendix. The graphs describe the probable variation of any year's growing season at the particular location chosen. As an example, one can assume the reader needs to know the probability of the growing season at Athens (Appendix figure 1) being longer than 210 days. He would locate the number of days (210 days) along the vertical side of the graph, then move horizontally until intersecting the slanted line given for Athens. Looking vertically from this point of intersection, the scale at the top of the graph gives the probability that a growing season longer than 210 days would occur. In this case, the probability would be 30 percent. The scale at the bottom of the graph gives the probabilities of growing season being shorter than the selected period of days. In this example, there would be a 70 percent chance of a shorter growing season than 210 days occurring in that particular year.

14

ALABAMA AGRICULTURAL EXPERIMENT STATION

CLIMATIC FEATURES

Local variations in freeze climate and length of growing season make analysis of Alabama's cold climate interesting. Factors such as topography, air drainage, location of water bodies, soil and vegetation types, as well as radiative characteristics of the terrain, create a complex arrangement of relatively cold and warm areas across the State. The climate of freezing temperatures primarily is influenced by atmospheric processes ongoing during those times of day when temperatures normally approach their lowest point. It is during these nighttime and early morning hours the above mentioned factors have their greatest influence on the local freeze climate and, hence, the character and length of growing season. This is when we need to examine these processes as a basis for climatic interpretation. Freeze patterns evolving from north to south within Alabama become the basis by which limits to growing season are defined. The prominent climatic features which show up in freeze analysis across the State often result from general changes in topography. Other physical influences that contribute to modifying the temperature environment may be less evident because of their lack of continuity or degree of influence over any geographic distance. The climatic distribution of first and last freeze dates is far from being a uniform and evenly distributed north to south pattern. Instead, considerable variation in the arrangement of low temperatures occurs. Figure 5 describes the climatic features that show up in growing season analysis within Alabama. Blue and red arrows lie along the axes of these climatic features and point in the direction of their major trends of influence. These are cold and warm anomalies that give a generalized interpretation of how the growing season climate is distributed within the State. It might be inferred from the analysis (based on normal length of growing season) that certain areas of the State have a propensity toward shorter growing season (blue arrows) while in others the threat of an earlier and later freeze may not be as great (red arrows). This assumption can only be made in a general way, however, since defining more localized climatic environments was not the purpose. Each of the climatic features was assigned a number in the text that follows so that during the discussion the reader may relate them to the map (figure 5), also numbered. Figure 6

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

15

Trends

FIG. 5. (:limatic features haled
seaso)n.

(on geographic variations in normal

length of growing

ALABAMA AGRICULTURAL EXPERIMENT STATION

F eet

1500 1000

750
0 25 50 75 Miles 500 250 100 0

I opograpIhe of Al~aama. 1 lbunia The ( nix crsit Of \hlabaima Priiss tioii Atlas oj oe \cil G. Line))atk, Director d( Eitoir, Chrh T. Trx loir ( artogra~phic Dir)tor cop

IG. I(i.

Reintedl h%\ periidoof

right 1973, p..

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

Coastal Plain Piedmont

Ridge

a

Valley
Plateau

Cumberland

ii F IG. 7. Phys iog~raph1ic regions ad( mIajor rivecrs w..ithin

lahatna.

18

ALABAMA AGRICULTURAL EXPERIMENT STATION

provides a general reference to the topography of Alabama. The physiographic regions and major river systems within the State are shown in figure 7. In both north and south Alabama, cold air drainage into interior valleys and broad topographic lowlands distinctly influences late spring and early fall frosts. This "valley effect" is especially noticeable where anomalies of cold climate are found oriented along some of the important rivers and topographic basins within the State. These become favorable channels down which cold air can feed southward or collectively pool during freeze nights. This phenomenon considerably shortens growing seasons in some of the northeastern valleys where the average growing season may last for a period of less than 190 days. At Valley Head, one of the colder observation sites in the State, the freeze-free period normally lasts only 181 days. Upland areas of north Alabama, like Sand Mountain, often fare much better with growing seasons of a more favorable length for vegetable and field crops. In northern parts of the State, two major cord regions occur where significantly shorter growing seasons seem to be the climatic rule. One of these regions, number 1 (figure 5), extends from the northeastern valleys and ridgelands southward to cover the piedmont and lower valleys of eastern Alabama. Here, the Coosa River forms a broad and predominately cold valley almost enclosed by higher terrain. Growing seasons are characteristically just over 200 days long throughout the valley, but become considerably shorter in some of the upland valleys to the east. From the lowlands of the Coosa River, elevations rise sharply into western Georgia. This is the eastern Piedmont with rolling, hilly terrain and some higher ridges. Shorter growing seasons are the rule across these uplands due to their prominent exposure to cold temperature advection down the Appalachian chain and the normal decrease of temperature that occurs with more elevated terrain. These factors are even more pronounced in the upland valleys and on the eastern slopes of the ridges. Variations in topography make this perhaps one of the most complex areas of the State in which to conduct freeze analysis and then generalize about local climate. Across the State, another cold feature, number 2, shows up in growing season analysis along those river valleys which drain southwest from the Cumberland Plateau onto the gently rolling,

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

19

upper Coastal Plain. In northwest Alabama, the axis of this climatic feature lies closely along those valleys that make up the eastern watershed into the Tombigbee River. Cold air moving down these valleys on freeze nights often results in the lowest temperatures being reported in the State. Some of the colder observation sites are within Marion, Fayette, and Lamar counties near communities situated in lowland areas. Reporting stations at Hamilton and Winfield experience growing seasons during an average year of 190 days or less. For some distance southward and extending across the lower basins of the Alabama and Tombigbee rivers in southwest Alabama, the feature maintains its identity as a local climate susceptible to freeze and shortened growing seasons. Some of the colder lowlands of south Alabama actually experience earlier and later frosts than in northern parts of the State. At Pittsview, in Russell County, number 3, the growing season is quite often short enough to rival many of the coldest locations in north Alabama. This results from a local terrain favorable to downslope drainage of cold air and the low heat capacity of the area's light textured, sandy-loam soil. In the evening, temperatures fall off both earlier and more rapidly as they respond to more pronounced surface cooling. Just the opposite effect may occur in poorly drained lowlands during a wet season when abundant soil moisture or areas of standing water alter the radiative character of the surface. Use of infrared satellite imagery suggests that on nights suitable to radiational freeze, wet lowlands may act as sources of warmth in restricting the fall of temperature. The radiative characteristics of wet soils results in their cooling more slowly than would dry soils. This phenomenon at least partially accounts for the longer growing seasons which overlie the braided pattern of streams and swamplands north of Mobile Bay, number 4. Some of the colder valleys in the State are found on the lower coastal plain. The drainage systems of the Conecuh and Pea Rivers, number 5, form a distinctly cold natured and frost susceptible region in the extreme southern counties. A strong "valley effect" results from long, almost straight-line valleys which serve as channels for cold air. The orientation of the valleys and tributaries along a direction favorable to normal temperature advection is another influencing factor. On the lower flood plain of these rivers, low temperatures are often the coldest in south Alabama on nights favorable to strong surface radiation and cold

20

ALABAMA AGRICULTURAL EXPERIMENT STATION

air drainage. An average growing season of 212 days at Brewton, Alabama, is usually about 20 to 30 days shorter than most other parts of the State south of the Alabama River. Just as the lay of the land influences cold temperature patterns that conform to lowland areas of the State, elevated terrain usually experiences a comparatively warm climate during the cold season. Freezing temperatures are generally less frequent and severe than in the colder lowlands. Over the southern interior of the State, growing seasons become prolonged where elevated terrain contributes to lessened freeze severity. Warm temperature anomalies show up in freeze analysis as concentric, elongated areas, bending northward and winding along topographic divides or uplands. One such area of broken uplands, number 6, extends from the southeast corner of the State in a westward arc along and paralleling the southern drainage of the Alabama River. It eventually forks into two arms, one bending northward into the Black Warrior River basin and the other turning southward into Monroe County. In the higher terrain throughout this region, growing seasons average from 240 to 250 days. Another prominent warm feature is located over the basin of the Black Warrior River, number 7. Freeze analysis shows a sharp bending of lines northeastward along this valley indicating the characteristics of a warm local climate. This feature appears to be a contradiction. Basin topographies are most often associated with cold microclimates. Part of the disparity is inherent in the analysis that must allow for pronounced cold anomalies found to either side of the Warrior Basin. Raised topography surrounds much of the upper portion of the valley with considerably higher terrain to the north and northeast. Elevation differences vary between 500 and 1,000 feet from the valley floor to ridge tops within a reasonably short geographic distance. Downslope winds over these ridge tops, as well as the protection they afford the valley from cold winds out of the north and east, may partially explain the effects that result in a longer growing season. Another factor could be the valley's open exposure to southerly winds and a rather broad and elevated valley floor which rises toward the northeast. Other effects may have resulted from observation sites located near water bodies and population centers. Across the Tennessee Valley, another warm feature shows up in analysis, number 8. Available data only partially supports the presence of this warm anomalie which appears more

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

21

questionable than those already discussed. The 220-day growing season at Muscle Shoals probably results from the warm exposure of this particular observation site. In all, there are about eight of these climatic features which appear distinctly on maps of freeze and growing season analysis in Alabama. When using the maps, one can determine whether a location in the State lies within one of these relatively cold or warm regions of local climate. Local differences, however, on a smaller scale of within 300 to 500 square miles might result in an erroneous interpretation of one's particular freeze climate. Therefore, for best results, the maps should be used in this manner only to draw generalized conclusions about the distribution of climate over a larger scale area. The maps are certainly valuable for gaining a regional interpretation of cold climate relationships within the State. We should also mention that any climatic interpretation depends considerably upon the individual characteristics of the meteorological sites chosen for analysis. Official climatological reporting stations, however, are normally situated at locations believed representative of surrounding countryside.
SUMMARY

Probable lengths of growing season have been described in graphs for seventy-three locations within Alabama. These were derived from a normal distribution of past growing seasons taken from each station's climatic record. In addition, the analysis of growing season was broadened to include examination of certain anomalous features found in Alabama's temperature climate. Overall, about eight of these climatic features can be described and related to environmental factors that have affected their formation.

22

ALABAMA AGRICULTURAL EXPERIMENT STATION

BIBLIOGRAPHY (1) (2) (3)
(4)

(5) (6)

GALLUP, J. R., 1979. Climate of Freeze in Alabama, Auburn University, (Ala.) Agr. Exp. Sta. Ag Weather Series No. 17, Auburn, Ala., 36 pp. GEIGER, R., 1965. The Climate Near the Ground. Harvard University Press, Cambridge, Mass. 611 pp. KISH, A. J., 1978. The Length of the Growing Season in South Carolina. S.C. Agr. Exp. Sta. Bull. 611, Clemson, S.C. 23 pp. LINEBACK, N. G., ET. AL., 1973. Atlas of Alabama. University of Alabama Press, University, Ala. 138 pp. THOM, H.C.S. AND SHAW, R.H., 1958. Climatological Analysis of Freeze Data for Iowa. Monthly Weather Review, 86, 251-252. U.S. DEPT. OF COMM., 1947-1978. Climatological Data (Alabama Section). NOAA, Environmental Data and Information Svc., Asheville, N.C.

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

23

2

APPENDIX
STATION INDEX PROBABLE LENGTHS OF CROWING SEASON

Station
Albertville

Appendix figure

Station

Appendix figure

........................ 1
1

Andalusia.........................2 Anniston..........................1 3 Ashland ..........................
Athens

Hamilton ......................... Headland.........................8 Heflin ........................... Highland Home....................
Lafayette

7
8 8

...........................

1 Auburn Bankhead L&D....................2 Bar Minette.......................2 Bel eMina........................1 3 Bessemer ......................... Birmingham.......................3 2 Brantley .......................... 2 Brewton .......................... Bridgeport........................3 Calera ........................... 3 4 Camp Hill ........................ 4 Centre ........................... Centreville........................4 5 Chatom .......................... Childersburg......................5 5 Clanton .......................... 4 Clayton .......................... 6 Coden ........................... Dayton...........................4 Demopolis L&D................... 5 Double Springs....................6 6 Fairhojpe ......................... Falkville..........................5 Fayette...........................8 Florence..........................7
Frisco

.........................

.........................

9

Livingston ........................
Madison.........................

Marion Junction Martin Dam.......................
Minter........................... Mobile

...................10
9 10 11

10

9

..........................

Montgomery......................9
Moulton

Muscle Shoals

Oneonta.........................11 Ozark........................... 11
Prattville.........................
Red Bay.........................

......................... 10 .....................10
11 12

Redstone Arsenal

Robertsdale ....................... Rockford ........................
Rock Mills.......................

..................12
11 12

12
...... 12

Russellville................. Sand Mountain Scottsboro........................
Selma

Saint Bernard.....................13

....................13
14 13 15 13
14

...........................

Sylacauga........................14
Talladega........................

Gadsden..........................7 Geneva...........................8 7 Greensboro ....................... 7 Greenville ........................ Guntersville.......................6 9 Haleyville ........................

City........................6

Thomasville......................

Troy ............................
Tuscaloosa....................... Union Springs Valley Head......................

.....................14
15
15

13
15

V ernon..........................

Waterloo

..............

...........

24

ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer 90 80 70 60 50 40 30 20 10 250 Auburn 240 Anniston 230 U)

Albertville Belle Mina Athens

o " 220 '4o a,

E 210 3
z

200

190

180

I

I

I

I

I

10

20

30 40 50 60 70

80

90

Probability of a growing season being shorter
APPENDIX FIG. 1

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

25

Probability of a growing season being longer 10 80 70 60 50 40 30 20 90 Bay Minette 280 Andalusio 260
in

Bankhead LED S 240 E Z 220 Brontley
Brewton

200

180

I

I

I

I

I

I

I

10

20

30 40 50 60 70

80

90

Probability of a growing season being shorter

APPENDIX FIG. 2

26

ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer 240 90 80 70 60 50 40 30 20 10 Birmingham

Ashland
230 Bessemer

220

Calero Bridgeport

0 210 -o

o

z

E 200
1800

170

90 30 40 50 60 70 80 being shorter Probability of a growing season 10 20
APPENDIX FIG. 3

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

2

27

Probability of a growing season being longer
90 270[

80

70 6050 4030

20

1O

Clayton

260

250

Dayton

240

Centreville

0

-v 230
'4-

0

E 220

Centre Camp Hill

Z
210

200

190

180

90 20 30 40 5060 70 80 10 Probability of a growing season being shorter
r

APPENDIX FIG. 4

28

ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer 90 80 70 60 50 40 30 20
I

SII

I

I

I

I

O10 Demopolis L&D

Chatom

Clonton

'0 O

.-

,

Childersburg Folkville

E z

10

20

30 40 50 60 70

80

90

Probability of a growing season being shorter
APPENDIX FIG. 5

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON
__ _ ___ ___ ___ __~ __ ____ _ ____ _ _ _2

2

29

Probability of a growing season being longer 90 80 70 60504030 20 10 Fairhope 00 Coden 80

0 *0
r4-

60

Frisco City

0 GL .0

E

:40

Guntersv ille Double Springs

Z
20

I

180'l 10

, 20

l I I 30 4050 6070

80

90

Probability of a growing season being shorter

APPENDIX FIG. 6

30

ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer 90 80 70 60 50 40 30 I I I I I I 20 I 10

' Greenville
Greensboro

260

240
o S220 -Florence
-

Gadsden

Hamilton

E
z 200

180

160 10

I 20

I I I I I 30 40 50 60 70

I 80

I 90

Probability of a growing season being shorter
APPENDIX FIG. 7

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

31

3

Probability of a growing season being longer 90 280 80 70 60 50403020
I II
I I I

10
Headland

260

Highland Home Geneva

V

a
0

,

240

~220
E z 200

Fayette Heftin

180

10

20

30 40 50 6070

80

90

Probability of a growing season being shorter
APPENDIX FIG. 8

32

32 ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer 90 80 10

70,6050403020
III
I I

260

r

I

1Montgomery

Martin Dam

250 Lafayette 240
IN
.0

Livingston 230

9-

E

z

220

Haleyville

210

200

190 10 20 30 40 5060 70 80 90

Probability of a growing season being shorter
APPENDIX FIG. 9

CLIMATIC FEATURES, AND THE LENGTH OF GROWING, SEASON,33 _ ~________

33

Probability of a growing season being longer 90 270 80 I' 70 60 50 40 30 20 10 Minter

260

250

Marion Junction Muscle Shoals

240
U) C
°t-

230
.O

E Madison Moulton

2 220

210

200

190 10 20 3040506070 80 90

Probability of a growing season being shorter
APPENDIX FIG. 10

34

34 ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer 90 300 Robertsdale
280

80 70 6050403020

10 Mobile

280

Ozark

> 06 260
40

Prattvil le

Q

240

z

E

220
200

Oneonta

180 10

20

30 40 5060 70

80

90

Probability of a growing season being shorter
APPENDIX FIG. 11

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON
-

35

3

Probability of a growing season being longer 90 80 70 60 504030 20 10
240I
I I I I I I

Bay 230 Rock ford Reds tone enat
Ars

220
N)

Rock kMills Russsetiville 210

0 .0
v-

E

200

Z
190

180

170I

1

I

I

I

I

I

10

20

30 4050 6070

80

90

Probability of a growing season being shorter
APPENDIX FIG. 12

.36

36 ALABAMA
_ I_

AGRICULTURAL
_ _l l

EXPERIMENT STATION
I

I _

Probability of a growing season being longer 90
I I-

80 7060 50 4030

20

10 Selma

Thomasville Tuscaloosa

N)

A
I.-

0 .0

Sand Mountain Saint Bernard

E
2

180'O

I

I

U

U

I

I

I

10

20304050607080

90

Probability of a growing season being shorter
APPENDIX FIG. 13

CLIMATIC FEATURES AND THE LENGTH OF GROWING SEASON

37

3

Probability of a growing season being longer 90 80 70 60 504030 20 10
270

Troy
260

20Union

Springs

250

240

S230
0

Sylacauga
-°

220

zy

3

Scottsboro

I

10

20

304050607080

90

Probability of a growing season being shorter

APPENDIX FIG. 14

38

38 ALABAMA AGRICULTURAL EXPERIMENT STATION

Probability of a growing season being longer

Toalladega
220 Vernon 210 Waterloo

u, >~200 0 4-

Valley Head

G)

190

E

z
180

170

1601

10

20

1

30 40 50 6070

V

I

I

I

I

I

I

80

90

Probalbility of a growing season being shorter
APPENDIX FIG. 15

AL1BLKN LNIN LI{M11

tulril rest°urc unit in
c\(r et\tVtj( ) so il area,.

ci

\nbhurn lIn ixersitx
sereN ft s the needs o

restrN , ad horrlttu-l p)rtxlIuCers in each retln bc in AIltata I'ver ct.i zeni of the State has ta stake in this research I pror"111,since 11N, ady'antat~ C fr )nI nexV
I it. i\'d\ 5t tn tIOprtx)l.U(. ing and handling; L1ar11 pr~cltitts diretv tihenefits the tmunlin~l pubiR.
K)

K

® Main Agricultural Experiment Station, Auburn.
-E.

V. Smith Research Center, Shorter.

1. Tennessee Valley Substation, Belle Mina. 2. Sand Mountain Substation, Crossville. 3. North Alabama Horticulture Substation, Cullman. 4. Upper Coastal Plain Substation, Winfield. 5. Forestry Unit. Fayette County. 6. Foundation Seed Stocks Farm, Thorsby. 7. Chilton Area Horticulture Substation, Clanton. 8. Forestry Unit. Coosa County. 9. Piedmont Substation, Camp Hitl. 10. Plant Breeding Unit, Tallassee. 11. Forestry Unit, Autauga County. 12. Prattville Experiment Field. Prattville. 13. Black Belt Substation. Marion Junction. 14. The Turnipseed-tkenberry Place. Union Springs. 15. Lower Coastal Plain Substation, Camden. 16. Forestry Unit, Barbour County. 17. Monroevitle Experiment Field, Monroevilte. 18. Wiregrass Substation. Headland. 19. Brewton Experiment Field, Brewton. 20. Solon Dixon Forestry Education Center, Covington and Escambia counties. 21. Ornamental Horticulture Field Station. Spring Hill. 22. Gulf Coast Substation, Fairhope.