Severe Thunderstorm Warning 142, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
140 PM CST FRI MAR 10 2000

OVER THE U.S. ON VAPOR IMAGERY THIS AFTERNOON A STRONG SHORTWAVE WAS
MOVING THROUGH THE SOUTHERN PLAINS WITH GOOD DRYING...PUSHING INTO
WEST TEXAS. ELEVATED CONVECTION WAS NOTED OVER THE NW ARK-LA-TEX
REGION AND WAS DEVELOPING TOWARD THE WESTERN SECTIONS OF THE
FORECAST AREA. VISIBLE IMAGERY SHOWED AN IMPRESSIVE CUMULUS FIELD
ALONG AND SOUTH OF THE STATIONARY FRONT FROM A BASTROP TO GREENVILLE
TO A TUPELO LINE WITH DEWPOINTS IN THE 60S. SCATTERED SHOWERS AND
STRONG THUNDERSTORMS WERE DEVELOPING OVER THE WESTERN SECTION OF THE
FORECAST AREA. AREA SOUNDINGS SHOWED GOOD LAPSE RATE AT THE
700-500MB LAYER OF 8 C/KM. ALL MODELS WERE A LITTLE SLOW IN
INITIALIZING THE PRECIP MOVING INTO ARKANSAS THIS MORNING.

LOOKING AT THE SHORT RANGE MODELS...IT APPEARS THAT WE WILL EXPERIENCE
2 ROUNDS OF CONVECTION. THE FIRST ROUND WILL BE FROM A SHORTWAVE ASSOCIATED
WITH THE ELEVATED CONVECTION OVER THE NORTHWEST ARK-LA-TX REGION. ALL
MODELS...ESPECIALLY THE NGM AND ETA BRING THIS ACTIVITY TO THE
NORTHWEST AND WESTERN SECTIONS THIS AFTERNOON. THE 2ND ROUND WILL
BE JUST AFTER MIDNIGHT AS THE SHORTWAVE TROF MOVES TOWARD THE LOWER
MISSISSIPPI VALLEY...BEFORE LIFTING NORTHEAST TO THE OHIO VALLEY ON
SATURDAY EVENING. ALL MODELS PUT THE REGION UNDER THE RIGHT REAR QUAD
OF UPPER JET WITH SOME UPPER DIVERGENCE OVER THE NORTH HALF OF THE
REGION. THE LOW LEVEL JET DOES NOT LOOK VERY IMPRESSIVE AS IT BECOMES
WESTERLY BY 06-12Z SATURDAY. IN THE LOW LEVELS THERE WILL BE SOME
SPEED OR VERTICAL WIND SHEAR. CAPE VALUES WILL RANGE FROM 1500 T0
AROUND 3000. ON THE SURFACE SHORTWAVE TROF WITH THE AID OF LOW LEVEL
BAROCLINICITY AND A WAVE COMING OUT OF THE SOUTHERN PLAINS...WILL
MOVE THE FRONT THROUGH THE REGION TONIGHT INTO SATURDAY MORNING.
WITH THE SLOW MOVEMENT OF THE FRONT THIS EVENING...EXPECT SOME
LOCALLY HEAVY RAINS OVER ALL SECTIONS OF THE REGION. ALSO WITH THE
EQUIVALENT POTENTIAL TEMPERATURE RIDGE...EXPECT A SQUALL LINE WILL
FORM JUST AHEAD OF THE FRONT THIS EVENING AND WILL MOVE OVER THE
LOWER MISSISSIPPI VALLEY OVERNIGHT INTO SATURDAY MORNING. EXPECT THE
SQUALL LINE TO MOVE THROUGH THE EASTERN SECTIONS EARLY SATURDAY.
CROSS SECTIONS SHOW DEEP MOISTURE AND GOOD VERTICAL VELOCITIES WITH
THIS SYSTEM. THE ETA/NGM MODELS SHOW PRECIPITABLE WATER OF AROUND
1.5 INCHES...WITH K-INDEXS OF AROUND 30. FAVOR THE NGM MODEL WITH
THE LOW LEVEL AND UPPER FEATURES...AS WELL AS THE PLACEMENT OF THE
BEST MEAN MOISTURE AND QPF AMOUNTS NEAR THE FRONT. SO WITH THIS IN
MIND WILL PUT IN A FEW POSSIBLY SEVERE FOR TONIGHT AND FOR THE EAST
EARLY SATURDAY MORNING. LOOKING AT SATURDAY THE RAINS WILL BE ENDING
FROM THE WEST AS THE FRONT EXITS THE REGION. AVN MODELS SHOWS A
ZONAL UPPER PATTERN AS SURFACE HIGH PRESSURE BRINGS ANOTHER ROUND OF
DRY WEATHER FOR SATURDAY NIGHT INTO SUNDAY.

AS FAR AS POPS ARE CONCERNED WILL GO CLOSER TO FAN POPS FOR TONIGHT AND
LEAN TOWARD NGM POPS FOR SATURDAY. WITH TEMPERATURES WILL FAVOR A COMPROMISE
OF THE SIMILAR NGM AND FAN GUIDANCE FOR TONIGHT. ETA TEMPS LOOKED TO
BE A LITTLE WARM. OTHERWISE ALL GUIDANCE WAS GENERALLY SIMILAR FOR
SATURDAY THROUGH SUNDAY.

QPF DISCUSSION...NCEP QPF AMOUNTS APPEAR TO BE ON TRACK. FOR THE BEST
AMOUNTS TO BE IN THE NORTHERN HALF OF THE FORECAST AREA FOR TONIGHT
THROUGH SATURDAY...WHERE UPPER LEVEL DYNAMICS WILL BE BETTER.

IN THE EXTENDED...THE 00Z MRF SHOWED A DRY ZONAL PATTERN FOR MONDAY.
IT BRINGS SHORTWAVE TROF INTO THE SOUTHERN PLAINS FOR TUESDAY...AS
LOW LEVEL MOISTURE INCREASES ACROSS THE REGION. A NEARLY CLOSED LOW
DEVELOPS OVER THE SOUTHERN PLAINS AS CONVECTION DEVELOPS TUESDAY AND
WEDNESDAY...PRIMARILY OVER THE SOUTHERN SECTIONS...WHERE MEAN
MOISTURE WILL BE DEEPER.A DISSIPATING FRONT WILL BE MOVING THROUGH
THE LOWER MISSISSIPPI VALLEY ON TUESDAY AND WEDNESDAY.
THE CANADIAN MODELS SHOWED A BROAD TROF OVER THE REGION ON TUESDAY
AND WEDNESDAY. IT ALSO SHOWED A WEAKENING FRONT MOVING THROUGH
THE REGION AS WELL. THE MODEL DISPLAYED GOOD MEAN MOISTURE FOR
CONVECTION DURING THAT PERIOD. THE NOGAPS SHOWED THE BEST MEAN
MOISTURE SOUTH AND WEST OF THE REGION. SO WITH THIS IN MIND
WILL PUT CHANCE OF RAIN AND THUNDERSTORMS FOR TUESDAY AND WEDNESDAY.

PRELIM NUMBERS...
JAN 056/060 031/058 038 8500
MEI 058/062 033/062: 036 7600

.JAN...
MS...NONE.
AR...NONE.
LA...NONE.

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