2001 JACKSON, MISSISSIPPI (JAN)

Jackson is located on the west bank of the Pearl River, about 45 miles east of the Mississippi River and 150 miles north of the Gulf of Mexico. The nearby terrain is gently rolling with no topographic features that appreciably influence the weather. The National Weather Service Office is nearly 7 miles east–northeast of the Jackson Post Office and over 5 miles southwest of the Ross Barnett Reservoir. Alluvial plains up to 3 miles wide extend along the river near Jackson, where some levees have been built on both sides of the river.

The climate is significantly humid during most of the year, with relatively short mild winters and long warm summers. The Gulf of Mexico has a moderating effect on the climate. Cold spells are fairly frequent in winter, but are usually of short duration. Sub–zero temperatures rarely occur. Temperatures occasionally exceed 80 degrees in mid–winter. In summer, temperatures reach 90 degrees or higher on about two–thirds of the days, 100 degree readings are infrequent. Extended periods of very hot weather are rare. On unusual occasions, temperatures at night may drop into the 50s, even in July or August.

Snowfall averages less than two inches per season, with nearly two–thirds of the seasons having only a trace of snow or none at all. Ice storms occasionally cause major damage to trees and power lines during the winter or early spring season. Rainfall is abundant and fairly well–distributed throughout the year. The area does not have a true dry season. However, the six–month period, June through November, is relatively dry in comparison with the December through May period when 60 percent of the annual precipitation can be expected.

Excessive rainfall may occur in any season. In spite of the normally abundant rainfall, fairly serious droughts occasionally occur during the summer or fall season. Tropical disturbances, including hurricanes and their remnants, are infrequent. However, those that pass near or visit the Mississippi Coast in the summer or early fall may bring several days of heavy rain to the Jackson area.

Thunderstorms can be expected on an average of 65 days a year, usually occurring in each month. They are most frequent in summer when they occur on about one-third of the days. At other times of the year, thunderstorms are usually associated with passing weather systems and are likely to be attended by higher winds than in summer. Severe thunderstorms normally affect portions of the metropolitan area a few times each year.

NORMALS, MEANS, AND EXTREMES

JACKSON, MS (JAN)

LATITUDE:    LONGITUDE:    ELEVATION (FT):    TIME ZONE:    WBAN: 03940

32 19′ 11″ N  90 04′ 39″ W  GRND: 293  BARO: 296  CENTRAL (UTC + 6)  

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.