Severe Thunderstorm Warning 23, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
230 PM CST SUN JAN 9 2000

TIS AN INTERESTING TIME TO FORECAST IN. FIRST...LETS TAKE A LOOK AT
THE SYNOPTIC PATTERN. MID/UPPER LEVEL HIGH PRESSURE STILL CENTERED
OVER CARIBBEAN AND NEAR HAWAII WITH MEAN TROUGH OVER CENTRAL US TO
OFF BAJA. IN THE LOWER LEVELS...HIGH PRESSURE NEAR THE FOUR CORNERS
AND EASTERN CARIBBEAN WITH WEAK LOW TRYING TO DEVELOPING OVER EAST
TEXAS AND PRETTY STRONG SYSTEM OVER WESTERN QUEBEC AND SURFACE
TROUGH/FRONT STRETCHING IN BETWEEN.

FOCUSING CLOSER TO THE FA...GOOD ISENTROPIC UPGLIDE IN THE LOWER
LEVELS(300K AND BELOW) OVER THE FA INTO TENN RIVER VALLEY. 850MB
WIND MAX(LOOKS TO BE MAIN CAUSE OF PRECIP LAST NIGHT) HEADING INTO
THE TENN RIVER VALLEY WITH A RESIDUAL BAND OF LIGHT PRECIP OVER
SOUTHEASTERN FA. BOUNDARY OVER FA LOOKING TO ALIGN WITH...BUT ABOUT
100 MILES WEST OF ENHANCED CLOUDS OVER SOUTHEAST MS. THIS BOUNDARY
WILL BE ENHANCED THROUGH THE AFTERNOON WITH THE CLEARING OF STRATUS
WEST OF THE ENHANCED CLOUDS.

MODELS PRETTY SIMILAR IN THE FIRST 24 HR FORECAST PERIOD IN THE
MID/UPPER LEVELS(SURPRISE...SURPRISE). GOOD ISENTROPIC UPGLIDE IN THE
LOWEST LEVELS(285K-300K). WESTERN EDGE OF BEST HUMIDITY COINCIDES
WITH WESTERN EDGE OF FA...MORE OR LESS. DIFFERENCES STILL ARISE IN
THE LOW LEVELS...MAINLY WITH SPEED OF APPROACHING FRONT. AVN STILL
THE FASTEST BY 6 HOURS AT F24(COMPARED TO ETA) WITH NGM HOT ON ITS
HEELS(4 HOURS AHEAD OF ETA). ALL MODELS HAVE STRENGTHENING 850 JET
RIGHT OVER FA THIS AFTERNOON INTO THIS EVENING...BEFORE IT MOVES OFF
NORTHEAST AFTER MIDNIGHT INTO MONDAY AND OUT OF OUR LIVES.
HELICITIES IN THE LATE AFTERNOON TO EVENING TIME FRAME IN THE 200 -
500 M^2/S^2 RANGE WITH CAPES 700 -1300 J/KG. BEST VALUES ARE THIS
EVENING..MAINLY ALONG AND EAST OF THE NATCHEZ TRACE. TAKING A LOOK
AT MODEL SOUNDINGS...INCREASING HELICITY VALUES MAINLY DUE TO
STRENGTHENING OF 850 MB JET. FEEL BEST PHASING OF JET DYNAMICS...
SHORTWAVE DYNAMICS..ETC...LOOKS TO BE ALONG AND WEST OF I-55...ALONG
AND NORTH OF I-20. GENERALLY UNIDIRECTIONAL FLOW PATTERN OVER FA
LENDS ITSELF TO A LINE TYPE EVENT WITH EMBEDDED MINI SUPERCELLS.
QUESTION AT THIS POINT WILL BE EXACTLY WHEN AND WHERE THINGS WILL
TAKE OFF FROM. HAVE A SNEAKING SUSPICION...THINGS WILL FIRE FIRST IN
SOUTH CENTRAL LA IN AREA OF BEST INSTABILITY WEST OF CLOUDS. THIS IS
ONLY A GUESS AT THIS POINT...THOUGH. GENERAL MOVEMENT LOOKS TO BE
TOWARDS THE NORTHEAST WITH INDIVIDUAL CELL SPEEDS IN THE 40-50 MPH
RANGE. ALL IN ALL...LOOKS LIKE AN INTERESTING EVENING.

FOR THE REST OF THE SHORT TERM...LOW LEVEL HIGH PRESSURE SETS UP
OVER THE GULF...CUTTING OFF LOW LEVEL MOISTURE. FRONT LOOKS TO BE
MORE OF A COOL FRONT WITH 1000-500MB THICKNESS VALUES DOWN ONLY AN
ANALYSIS LINE OR TWO. ETA MORE ENTHUSIASTIC WITH THE COOL SURGE THAN
NGM OR AVN(1000-500 MB). LOOKING AT LOW LEVEL 1000-850MB THICKNESS
VALUES EACH MODEL PRETTY CONSISTENT(EACH COMPARED TO ITSELF) FOR THE
MON - TUES TIME FRAME. CAN/T REALLY EXPLAIN FASTER AVN WARMUP IN THE
SHORT TERM FROM THE THICKNESS VALUES...THOUGH.

NOW THAT THE RAMBLINGS ARE OVER...AM GOING TO LEAN TOWARDS
ETA...SPEEDING IT UP A BIT IN THE FIRST TWO PERIODS. FRONT LOOKS TO
BE AT THE RIVER JUST AFTER 00Z...THEN THROUGH STATE BY SUNRISE. WILL
PROBABLY LEAN TOWARDS COOLER NGM DAYTIME TEMPS FOR TUESDAY. FOR
POPS...WILL PROBABLY GO WITH LIKELY SOUTHEAST...MAYBE EVEN
CATEGORICAL...GOOD CHANCE NORTHWEST TOWARDS REGION OF LESS
INSTABILITY AND COOLER TEMPS.

QPF DISCUSSION: SITUATION A LITTLE TRICKY AS AMOUNTS WILL DEPEND ON
SPEED OF THE SYSTEM OVER THE PLAINS AND WHERE THE COLD FRONT
INTERSECTS THE MOISTURE AXIS. RIGHT NOW...THE ETA SEEMS TO HAVE
THE POSITION OF QPF HANDLED WELL...BUT MAY BE OVERDONE UP NORTH
LOOKING AT CURRENT DEW PTS AROUND GLH AND GWO. NCEP HAS NO QPF UP IN
OUR THAT SAME AREA AT ALL WHICH SEEMS ODD SINCE THE AREA IS IN A
MODERATE RISK FOR THUNDERSTORMS TONIGHT. LEANING WITH AROUND 0.25
AMOUNTS NW ZONES AND INCREASING THESE AMOUNTS UPWARDS TO AN 1.00
BASIN AVERAGE OVER SE ZONES WITH THE CURRENT POSITION OF THE DEW
PT/THETA-E AXIS (BILOXI MS- BIRMINGHAM AL-NASHVILLE TN).

IN THE EXTENDED...ZONAL WEST TO NORTHWESTERLY FLOW IN THE MID/UPPER
LEVELS WILL SWING BEST DYNAMICS NORTH OF THE FA. DECENT SHORTWAVE
MOVING THROUGH THE FLOW OVER THE CENTRAL PLAINS WILL FORM SURFACE
LOW ON LEE SIDE OF COLORADO ROCKIES...THEN MOVE IT ALMOST DUE EAST
THROUGH THE EXTENDED. LOW LEVEL HIGH PRESSURE WILL MOVE SLOWLY
EAST...ALLOWING FOR SOME MOISTURE RETURN...BUT LOOKS LIMITED AT THIS
TIME.

PRELIMINARY NUMBERS:
JAN 048/063 037/069 043 6000
MEI 048/064 035/069 041 7-00

.JAN...
MS...NONE.
AR...NONE.
LA...NONE.
16/05