2001 ATLANTA, GEORGIA (ATL)

Atlanta is located in the foothills of the southern Appalachians in north–central Georgia. The terrain is rolling to hilly and slopes downward toward the east, west, and south so that drainage of the major river systems is generally into the Gulf of Mexico from the western and southern sections of the city and to the Atlantic from the eastern portions of the city.

The Gulf of Mexico and the Atlantic Ocean are approximately 250 miles south and southeast of the city, respectively. Both the Appalachian chain of mountains and the two nearby maritime bodies exert an important influence on the Atlanta climate. Temperatures are moderated throughout the year while abundant precipitation fosters natural vegetation and growth of crops. Summer temperatures in Atlanta are moderated somewhat by elevation but are still rather warm. However, prolonged periods of hot weather are unusual and 100 degree heat is rarely experienced.

With the mountains to the north tending to retard the southward movement of Polar air masses, Atlanta winters are rather mild. Cold spells are not unusual but they are rather short–lived and seldom disrupt outdoor activities for an extended period of time. Late March is the average date of the last temperature of 32 degrees in the spring and mid–November is the average date of the first temperature of 32 degrees in the fall, which gives an average growing season of about 234 days.

Minimum dry precipitation periods occur mainly during the late summer and early autumn. Maximum thunderstorm activity occurs during July, but severe local thunderstorms occur most frequently in March, April, and May, some spawning highly damaging tornadoes.

The average annual snowfall varies widely from year to year. A fall of 4 inches or more occurs about once every five years. Most snows melt in a short period of time due to the rapid warming which often follows the storm. Ice storms, freezing rain or glaze, occur about two out of every three years, causing hazardous travel and disruption of utilities. Severe ice storms occur about once in ten years, causing major disruption of utilities and significant property damage.

The Bermuda High pressure area has a dominant effect on Atlanta weather, particularly in the summer months. East or northeast winds produce the most unpleasant weather although southerly winds are quite humid during the summer. The generally light wind conditions contribute to the formation of an occasional early morning fog.

NORMALS, MEANS, AND EXTREMES

ATLANTA, GA (ATL)

LATITUDE: LONGITUDE: ELEVATION (FT): TIME ZONE: WBAN: 13874

33 38′ 25″ N  84 25′37″W  GRND: 971 BARO: 974  EASTERN (UTC + 5)

REFERENCE NOTES:

PAGE 1:

THE TEMPERATURE GRAPH SHOWS NORMAL MAXIMUM AND NORMAL MINIMUM DAILY TEMPERATURES (SOLID CURVES) AND THE ACTUAL DAILY HIGH AND LOW TEMPERATURES (VERTICAL BARS).

PAGE 2 AND 3:

H/C INDICATES HEATING AND COOLING DEGREE DAYS.

RH INDICATES RELATIVE HUMIDITY

W/O INDICATES WEATHER AND OBSTRUCTIONS

S INDICATES SUNSHINE.

PR INDICATES PRESSURE.

CLOUDINESS ON PAGE 3 IS THE SUM OF THE CEILOMETER AND SATELLITE DATA NOT TO EXCEED EIGHT EIGHTHS (OKTAS).

GENERAL:

T INDICATES TRACE PRECIPITATION, AN AMOUNT GREATER THAN ZERO BUT LESS THAN THE LOWEST REPORTABLE VALUE.

+ INDICATES THE VALUE ALSO OCCURS ON EARLIER DATES.

BLANK ENTRIES DENOTE MISSING OR UNREPORTED DATA.

NORMALS ARE 30–YEAR AVERAGES (1961–1990).

ASOS INDICATES AUTOMATED SURFACE OBSERVING SYSTEM.

PM INDICATES THE LAST DAY OF THE PREVIOUS MONTH.

POR (PERIOD OF RECORD) BEGINS WITH THE JANUARY DATA MONTH AND IS THE NUMBER OF YEARS USED TO COMPUTE THE MEAN. INDIVIDUAL MONTHS WITHIN THE POR MAY BE MISSING.

WHEN THE POR FOR A NORMAL IS LESS THAN 30 YEARS, THE NORMAL IS PROVISIONAL AND IS BASED ON THE NUMBER OF YEARS INDICATED.

0.* OR * INDICATES THE VALUE OR MEAN–DAYS–WITH IS BETWEEN 0.00 AND 0.05.

CLOUDINESS FOR ASOS STATIONS DIFFERS FROM THE NON–ASOS OBSERVATION TAKEN BY A HUMAN OBSERVER. ASOS STATION CLOUDINESS IS BASED ON TIME–AVERAGED CEILOMETER DATA FOR CLOUDS AT OR BELOW 12,000 FEET AND ON SATELLITE DATA FOR CLOUDS ABOVE 12,000 FEET.

THE NUMBER OF DAYS WITH CLEAR, PARTLY CLOUDY, AND CLOUDY CONDITIONS FOR ASOS STATIONS IS THE SUM OF THE CEILOMETER AND SATELLITE DATA FOR THE SUNRISE TO SUNSET PERIOD.

GENERAL CONTINUED:

CLEAR INDICATES 0–2 OKTAS, PARTLY CLOUDY INDICATES 3–6 OKTAS, AND CLOUDY INDICATES 7 OR 8 OKTAS. WHEN AT LEAST ONE OF THE ELEMENTS (CEILOMETER OR SATELLITE) IS MISSING, THE DAILY CLOUDINESS IS NOT COMPUTED.

WIND DIRECTION IS RECORDED IN TENS OF DEGREES (2 DIGITS) CLOCKWISE FROM TRUE NORTH. "00" INDICATES CALM. "36" INDICATES TRUE NORTH.

RESULTANT WIND IS THE VECTOR AVERAGE OF THE SPEED AND DIRECTION.

AVERAGE TEMPERATURE IS THE SUM OF THE MEAN DAILY MAXIMUM AND MINIMUM TEMPERATURE DIVIDED BY 2.

SNOWFALL DATA COMPRISE ALL FORMS OF FROZEN PRECIPITATION, INCLUDING HAIL.

A HEATING (COOLING) DEGREE DAY IS THE DIFFERENCE BETWEEN THE AVERAGE DAILY TEMPERATURE AND 65 F.

DRY BULB IS THE TEMPERATURE OF THE AMBIENT AIR.

DEW POINT IS THE TEMPERATURE TO WHICH THE AIR MUST BE COOLED TO ACHIEVE 100 PERCENT RELATIVE HUMIDITY.

WET BULB IS THE TEMPERATURE THE AIR WOULD HAVE IF THE MOISTURE CONTENT WAS INCREASED TO 100 PERCENT RELATIVE HUMIDITY.

ON JULY 1, 1996, THE NATIONAL WEATHER SERVICE BEGAN USING THE "METAR" OBSERVATION CODE THAT WAS ALREADY EMPLOYED BY MOST OTHER NATIONS OF THE WORLD. THE MOST NOTICEABLE DIFFERENCE IN THIS ANNUAL PUBLICATION WILL BE THE CHANGE IN UNITS FROM TENTHS TO EIGHTS (OKTAS) FOR REPORTING THE AMOUNT OF SKY COVER.