Severe Thunderstorm Warning 4, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
420 PM CST THU JAN 18 2001

AT THIS TIME...THINKING HAS NOT CHANGED CONCERNING FLOODING AND
SEVERE THUNDERSTORM POTENTIAL. POWERFUL...WELL ADVERTISED...
SHORTWAVE WILL AFFECT THE FORECAST AREA NEXT 24 TO 48 HRS WITH ALL
INGREDIENTS COMING TOGETHER FOR EXCESSIVE RAINFALL OVER NW 2/3RDS OF
AREA. OF PARTICULAR CONCERN IS AREA NW OF TVR TO GWO LINE WHERE
HEAVY RAIN FELL LAST NIGHT AND THIS AFTERNOON. FFG GUIDANCE VALUES
ARE VERY LOW IN THIS REGION. NEEDLESS TO SAY...WILL CONTINUE FLOOD
WATCH. WILL HOLD OFF ON EXPANDING FLOOD WATCH TO SE ZONES WHERE
SOILS ARE NOT AS WET AND WHERE HEAVIER RAINS WILL HOLD OFF UNTIL
LATE TONIGHT.

CONCERNING SEVERE WEATHER...WITH SURFACE WARM SECTOR HAVING PUSHED
WELL INTO SOUTHEAST MS SEVERE WEATHER THREAT HAS INCREASED PER SPC
DAY ONE OUTLOOK. WILL MENTION SEVERE THUNDERSTORM POSSIBILITY FOR
SOUTHEAST ZONES FOR TONIGHT.

RAIN WILL CONTINUE THRU FRI MORNING WITH THUNDERSTORMS STILL
POSSIBLE OVER ERN SECTIONS...BUT RAIN WILL DIMINISH IN THE AFTN AS
DYNAMICS BEGIN TO SHIFT RAPIDLY NORTHEAST. SNOW POTENTIAL IS A BIT
LOWER THAN PREVIOUSLY THOUGHT AS SURFACE TEMPS ARE FORECAST IN MODEL
SOUNDINGS TO REMAIN WELL ABOVE FREEZING. ONLY CONCERN IS VERY LOW
WET BULB ZERO HEIGHTS OF AROUND 800FT OVER NW PORTIONS OF AREA. HAVE
LEFT MENTION OF SNOW IN FORECAST...BUT TEMPERED WORDING DOWN A BIT
BASED ON LATEST MODEL TRENDS. NEW MESOETA FORECASTS SRN STREAM 500
MB VORT TO TRACK FROM EC LA TO NE MS FRI AFTN AND BEST SNOWFALL...IF
ANY WOULD OCCUR TO LEFT OF THIS TRACK. AFTER THAT...NRN STREAM VORT
APPROACHES LATE FRI/SAT AND ENOUGH LOW LEVEL MOISTURE SHOULD EXIST
FOR FLURRIES OVER NE HALF OF AREA. ALL IN ALL...QPF WILL LIGHT WITH
THE DEEP COLD ADVECTION AND SIGNIFICANT SNOW ACCUMULATIONS ARE NOT
EXPECTED. TEMPS WILL BE COLD AND HAVE FOLLOWED A MAV/FWC GUIDANCE
COMPROMISE. COULD SEE A FEW TEENS BY SUNDAY MORNING.

24 HR QPF DISCUSSION...MODEL OUTPUT TO THIS POINT HAS SIGNIFICANTLY
UNDERFORECASTED QPF. ETA QPF IS VERIFYING MUCH BETTER TODAY THAN
AVN...BUT BELIEVE THAT GIVEN IMPRESSIVE FEATURES COMING TOGETHER...
ACTUAL QPF WILL CONTINUE TO BE HEAVIER THAN 1 TO 2 INCH AMOUNTS
FORECASTED BY MODELS FOR 00Z FRI TO 00Z SAT TIME FRAME.

IN THE EXTENDED...MRF/UKMET/LATEST AVN SUGGEST A PROGRESSIVE BUT RATHER
AMPLIFIED PATTERN WITH MEAN TROFFING OVER THE MS VALLEY REGION AND
PERSISTENT RIDGING OVER THE WRN CONUS. SIGNIFICANT MID LEVEL
SHORTWAVES WILL MOVE OVER THE FORECAST AREA MONDAY AND POSSIBLY
AGAIN BY THURSDAY...BUT MOISTURE RETURN WILL BE LIMITED AND WILL
CONTINUE DRY FORECAST FOR NOW. IF PRECIPITATION CAN DEVELOP...SOME
QUESTION WILL EXIST CONCERNING PRECIP TYPE AS COLD AIR THAT MOVES IN
THIS WEEKEND WILL NOT MODIFY AS QUICKLY AS PREVIOUSLY THOUGHT.

PRELIM NUMBERS...
JAN 41/42/28/38/20 +92--
MEI 49/50/30/38/20 ++3--

.JAN...
MS...FLOOD WATCH THROUGH TONIGHT NORTHWEST OF BUDE TO PORT GIBSON TO
JACKSON TO GRENADA LINE.
LA...FLOOD WATCH TONIGHT.
AR...FLOOD WATCH TONIGHT.

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