Severe Thunderstorm Warning 170, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
300 PM CST SUN MAR 26 2000

A GOOD SOAKING FROM SHOWERS AND THUNDERSTORMS OCCURRED ACROSS MUCH
OF CENTRAL AND SOUTHERN PORTIONS OF THE FORECAST AREA THIS MORNING
SOUTH OF A BASTROP...LOUISIANA TO CANTON TO MERIDIAN LINE. MANY
AREAS RECEIVED FROM ONE TO TWO INCHES OF RAIN. THIS AFTERNOON...
SKIES HAVE CLEARED IN ALL BUT EXTREME SOUTHEASTERN AREAS ALLOWING
FOR A RAPID WARM UP AND DESTABILIZATION OF THE ATMOSPHERE. A STRONG
COLD FRONT...PRECEDED BY A PREFRONTAL TROUGH...WILL SWEEP EASTWARD
ACROSS THE AREA TONIGHT. EXPECT WIDESPREAD RAIN EVENT...MAINLY AFTER
MIDNIGHT...AS BEST VERTICAL MOTION IS EXPECTED TO BE OVER THE
FORECAST AREA BETWEEN MIDNIGHT AND SIX AM TONIGHT ACCORDING TO
LATEST ETA AND NGM MODEL FORECASTS. THE AVN MODEL ALSO SHOWS BEST
UPWARD VERTICAL MOTION OVER THE FA BETWEEN 06 AND 12Z...BUT HAS MORE
DRY AIR AT THE MID LEVELS. HOWEVER...AVN MODEL GUIDANCE FORECASTS
HIGHER POPS THAN THE NGM. WILL PLAN TO GO WITH AVN'S CATEGORICAL
POPS FOR TONIGHT IN WESTERN AREAS WITH SLIGHTLY LOWER POPS EAST. WILL
KEEP SOME LINGERING POPS IN ALL BUT NORTHWESTERN ZONES FOR EARLY
MONDAY MORNING.

FOR TONIGHT'S EVENT...SEVERE STORMS WILL BE A POSSIBILITY. WILL
MENTION IN ZONES. THE SPC SHOWS WESTERN HALF OF THE FA IN A MODERATE
RISK AREA FOR TONIGHT. FORECAST ETA MODEL HELICITIES WILL BE UP TO
500 J/KG IN WEST CENTRAL AREAS AT 06Z TONIGHT. AT THIS TIME...THE
BEST CAPES IN WEST CENTRAL AREAS ARE FORECAST TO BE AROUND 1000
J/KG. THE OPTIMUM CAPE/HELICITY AREAS ARE EXPECT TO DECREASE AS THEY
MOVE SOUTHEASTWARD ACROSS THE FA DURING THE NIGHT. THE ETA MODEL
SHOWS FORECAST AREA IN VICINITY OF THE LEFT FRONT QUADRANT OF THE
JET TONIGHT. A FLASH FLOOD WATCH MAY NEED TO BE CONSIDERED FOR LATE
TONIGHT IN CENTRAL AND SOUTHERN AREAS WHERE GOOD RAINFALL OCCURRED
THIS MORNING. HOWEVER...GOOD DRYING IS OCCURRING IN MOST AREAS THIS
AFTERNOON AND STORMS SHOULD MOVE RAPIDLY ACROSS THE AREA TONIGHT.
THEREFORE...AM NOT EXTREMELY CONCERNED ABOUT FLOODING EXCEPT IN
ISOLATED AREAS THAT EXPERIENCE THE MOST INTENSE RAINFALL TONIGHT.

FOR TEMPS...WILL STAY CLOSEST TO AVN GUIDANCE BUT WILL FORECAST
CLOSER TO NGM MOS GUIDANCE'S WARMER HIGHS FOR TUESDAY.

QPF DISCUSSION: IN DEVELOPING SHOWERS/STORMS OVER NORTHEAST LA AND
WESTERN MS...EXPECT POTENTIALLY HEAVY...LOCAL RAINFALL AMOUNTS OF
.75 TO 1 INCH. THIS PROG IS LOWER THAN GUIDANCE WHICH INDICATED AVERAGE
AMOUNTS OF 1 INCH OVER SAME AREA WITH AMOUNTS TO 1.5 INCH OVER SW
MS. BELIEVE HEAVY RAINFALL POTENTIAL WILL BE ADVERSELY IMPACTED BY
RAPID MOVEMENT OF ANTICIPATED STORMS AND SHIFT OF UPPER LEVEL AND
SURFACE WINDS TO A MORE WESTERLY COMPONENT 06Z TO 12Z. OUTSIDE THIS
AREA...RAINFALL AMOUNTS EXPECTED WILL AVERAGE FROM .1 TO .5 INCH...
GIVEN MOISTURE CONTENT OF AIRMASS AS REFLECTED BY HIGH PRECIPITABLE
WATER/DEWPOINT VALUES.

IN THE EXTENDED...STRONG SOUTHERLY FLOW RETURNS TO THE FA BY
WEDNESDAY WITH NEW SURFACE LOW IN PLACE OVER OKLAHOMA. BOTH MRF AND
CANADIAN MODEL TRACK THIS LOW ACROSS MISSISSIPPI ON THURSDAY. ON
FRIDAY...THE FA IS UNDER INFLUENCE OF STRONG ZONAL FLOW ACROSS THE
SOUTH. PRECIPITATION MAY BE LESS LIKELY FOR THE FA ON FRIDAY...BUT
CANNOT RULE OUT THE POSSIBILITY OF PRECIP UNDER THIS WEATHER
PATTERN. WILL THEREFORE HAVE CHANCE OF SHOWERS AND THUNDERSTORMS IN
THE EXTENDED FORECAST THROUGH THE PERIOD.

.PRELIM NUMBERS...
JAN 56/68/42/75 8200
MEI 57/69/41/74 7400

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

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