Severe Thunderstorm Warning 61, NWS Jackson, MS

AREA FORECAST DISCUSSION...CORRECTED TO ADD PRELIM NUMBERS...
NATIONAL WEATHER SERVICE JACKSON MS
345 PM CST SAT FEB 26 2000

PROGRESSIVE SHARP UPPER TROF PICKING UP A BIT OF SPEED AS
THUNDERSTORM ACTIVITY INCREASES OVER CNTRL/ERN AR AND LA. NOT A LOT
TO DECIPHER WITH ALL MODELS IN AGREEMENT ON PROGRESSIVE CONVECTIVE
COMPLEX SWEEPING EASTWARD ACROSS THE FORECAST AREA OVER NIGHT. TWO
BOUNDARIES OF NOTE LATE THIS AFTN...ONE AHEAD OF DEVELOPING COMPLEX
CURRENTLY USHERING RAIN-COOLED SFC AIR (TEMPS IN 50S) INTO WRN HALF
OF FORECAST AREA WHILE A DRY LINE/COLD FRONT PUSHES INTO THE WRN EDGE OF
THE COMPLEX. MOST OF CONVECTION IS ELEVATED AT THIS POINT WITH
STRONG SOUTHERLY FLOW FROM SFC TO 700MB BRINGING IN HIGH PRECIP
WATER VALUES FROM WESTERN GULF. ISENTROPIC UPGLIDE IN 295 TO 305K
LAYER HELPING TO FUEL TSTM ACTIVITY ABOVE STABLE SFC LAYER.

OVERNIGHT...THE DRYLINE/COLD FRONT WILL SWEEP EASTWARD ACROSS THE
FORECAST AREA. ALTHOUGH NO SEVERE TSTM ACTIVITY CURRENTLY IN
PROGRESS...WILL KEEP POSSIBILITY OF SVR TSTMS GIVEN DYNAMIC
PARAMETERS COMING INTO PLACE INCLUDING VERY FAVORABLE RIGHT ENTRANCE
REGION OF UPPER JET AND STRONG WIND FIELDS AND DEEP UPWARD VERTICAL
MOTION. HEAVY RAIN WILL ALSO BE A THREAT GIVEN PRECIPITABLE WATER
VALUES OVER 200 PERCENT OF NORMAL AND INCREASINGLY UNIDIRECTIONAL
WIND PROFILES FROM SFC TO 500 MB. HEAVY RAIN/SEVERE TSTM THREAT WILL
DIMINISH RAPIDLY FROM WEST TO EAST LATER TONIGHT WITH ALL MODELS
ENDING PRECIPITATION BY DAYBREAK.

FOR SUNDAY THRU MONDAY...SFC HIGH PRESSURE WILL BUILD ACROSS THE
REGION BRINGING CLEARING SKIES AND A BIT COOLER TEMPS. WAS CONCERNED
ABOUT STRATOCU DECK HANGING AROUND SUNDAY...LOW LEVEL THERMAL TROF
WEAKENS WITH TIME ALONG WITH LOW LEVEL COLD AIR ADVECTION. WITH
CLEAR SKIES AND SFC HIGH SUN NIGHT...SHOULD HAVE GOOD RADIATIONAL
COOLING AND WENT A LITTLE BELOW MOS GUIDANCE TEMPS.

QPF DISCUSSION...OUR RAIN WINDOW WILL REMAIN LIMITED TO A 12-18 HOUR
TIME FRAME ONCE IT BEGINS. RATHER IMPRESSIVE DEEP VERTICAL MOTION
AXIS CROSSES THE FORECAST AREA FROM 00Z TO 12Z ASSOCIATED WITH A
STRONG MID-UPPER LEVEL VORT MAX CROSSING NERN TX. A REDEVELOPING
SQUALL LINE FROM AROUND KGWO TO KTVR TO KLCH SHOULD ACCELERATE FROM
CURRENT 10 MPH EWD MOTION BY EARLY TONIGHT. PRECIPITABLE WATER
VALUES OF 1.2 TO 1.4 INCHES BECOME SQUEEZED FROM THE WEST WITH
VALUES BELOW .5 INCHES BY 15Z SUNDAY. NCEP FORECASTS LOOK REASONABLE
OF 1 TO 1.5 INCHES MAINLY OVER A 6 HOUR PERIOD...LOCAL 2 INCH SPOTS
ARE POSSIBLE.

IN THE EXTENDED...00Z MRF/00Z UKMET/12Z NCEP ENSEMBLES/12Z AVN ALL
IN THE SAME BALL PARK INDICATING THAT MEAN RIDGE POSITION WILL BUILD
ACROSS THE LOWER MS VALLEY TUESDAY AS A SHORTWAVE TROF DEVELOPS IN
MEAN TROF POSITION OVER SOUTHWEST CONUS. WILL KEEP AREA DRY TUESDAY
GIVEN THIS SCENARIO. THE SHORTWAVE TROF WILL WEAKEN AS IT APPROACHES
MEAN RIDGE...BUT IT APPEARS ENOUGH ENERGY AND RETURN FLOW COULD MAKE
IT TO THE LOWER MS VALLEY TO PRODUCE SOME SHOWER ACTIVITY. SO WILL
LEAVE CHANCE SHOWERS GOING WEDNESDAY. A STRONGER SYSTEM IS PROGGED
TO APPROACH FROM THE WEST LATE THURSDAY. WILL MENTION CHC OF SHOWERS
AND TSTMS THURSDAY AS THIS SYSTEM SHOULD DAMPEN RIDGE POSITION
ENOUGH TO BRING THREAT OF DEEP CONVECTION BY LATE IN THE DAY. TEMPS
WILL REMAIN ABOVE AVERAGE THRU THE PERIOD.

JAN BU 046/065 035/069 045 9-00
MEI BU 051/066 033/071 045 9100

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

43/40