Severe Thunderstorm Warning 341, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
205 PM CDT TUE MAY 9 2000

MODELS AGREE QUITE WELL ON THE PATTERN EVOLUTION THROUGH 48 HOURS.
OF COURSE QPF OUTPUT IS ANOTHER STORY...BUT WILL DEFER THAT THOUGHT
FOR A FEW PARAGRAPHS.

CONVECTION OVER NRN AR GOING THROUGH THE TYPICAL LATE MORNING/EARLY
AFTERNOON WEAKENING AS OF NOON...BUT EXPECT REINTENSIFICATION LATER
THIS AFTERNOON. CAPES OVER THE DELTA REGION PROGGED TO REACH 3000
J/KG LATE THIS AFTERNOON...AND WITH SHORTWAVE ENERGY PROVIDING LARGE
SCALE ASCENT TO OVERCOME THE CAP...STRONG STORMS WILL BE POSSIBLE.
HIGH CAPE/LOW SHEAR ENVIRONMENT MORE CONDUCIVE TO PULSE TYPE HAILERS
AND WET MICROBURSTS...WIDESPREAD SEVERE WEATHER AND/OR TORNADOES
UNLIKELY. DUE TO EXPECTED LOW AREAL COVERAGE OF SEVERE WILL NOT
MENTION IN ZONES...UNLESS SEVERE WEATHER IS ONGOING JUST UPSTREAM AT
ZONE RELEASE TIME.

SHORTWAVE LOBE AND ASSOCIATED COUPLET OF UPPER LEVEL DIVERGENCE/LOW
LEVEL CONVERGENCE BRUSH THE NORTHERN EXTREMES OF THE CWFA OVERNIGHT
AND EXIT INTO ALABAMA SHORTLY AFTER SUNRISE. CONCURRENTLY...THE
SURFACE COLD FRONT BEGINS TO STRETCH OUT E-W AS THE SOUTHERN END
LOSES ITS PUSH...AND THE FRONT REACHES ITS FARTHEST SOUTH POINT
ACROSS CENTRAL/SOUTH MS DURING THE DAY WEDNESDAY. TEMP FORECAST WILL
BE VERY TRICKY AND WILL BE HIGHLY DEPENDENT ON JUST HOW FAR SOUTH
THE FRONT GETS TONIGHT AND HOW FAR SOUTH IT STAYS WEDNESDAY. FIRST
INSTINCT WAS TO DISCARD THE NGM/AVN MOS FORECASTS OF NEAR 60 TONIGHT
AND WEDNESDAY NIGHT...BUT AFTER LOOKING AT UPSTREAM OBS OVER NORTH
TX BELIEVE THIS MAY BE PLAUSIBLE AT LEAST FOR TONIGHT. WILL RAISE
MOS MINS FOR WED NIGHT AS FRONT BEATS A HASTY RETREAT IN THE FACE OF
INCREASING LOW LEVEL SOUTHERLY FLOW. BACK TO PRECIP...BEST CHANCE
TONIGHT WILL BE IN THE NORTHERN CWFA WITH LESSER CHANCES TO THE
SOUTH. THIS IS COVERED WELL BY PREVIOUS FORECAST. WEDNESDAY PRECIP
FORECAST IS MORE PROBLEMATICAL AS SURFACE FRONT RESIDES UNDERNEATH
AN UNCAPPED AIRMASS AS PER ETA PROGS. AVN QPF...WHICH HAS BEEN FAR
MORE AGGRESSIVE THAN NGM/ETA QPF SINCE THE AVN WAS CHANGED TO T170
RESOLUTION...SHOWS A BULLSEYE OF AFTERNOON CONVECTION OVER THE
SOUTHERN CWFA WHILE ETA/NGM REMAIN GENERALLY DRY. CANADIAN MODEL
SIDES WITH THE ETA/NGM WHILE THE NOGAPS COMPROMISES BY PAINTING
SMALLER PRECIP AMOUNTS OVER A BROADER AREA THAN THE AVN. CANNOT
BRING MYSELF TO FORECAST NO POPS WITH THIS SCENARIO...AND WOULD
PREFER SLIGHT CHANCE POPS OVER ALL BUT THE FAR NORTH CWFA WHERE
COOLER AIR IN LOW LEVELS WILL BE SLIGHTLY DEEPER AND AIRMASS SHOULD
BE WEAKLY CAPPED. UPON FURTHER REVIEW...THIS THINKING IS IN
EXCELLENT AGREEMENT WITH THE PREVIOUS FORECAST. ANY PRECIP WOULD BE
DIURNALLY DRIVEN AND DIE OFF AFTER SUNSET. THURSDAY LOOKS DRY AND
WARM AS THE AIRMASS DRIES OUT AND HEIGHTS RISE. HAVE ONLY SEEN ONE
90F READING IN OUR CWFA SO FAR THIS SEASON /BELZONI LAST
SATURDAY/...BUT EXPECT QUITE A FEW ON THURSDAY.

QPF DISCUSSION...MODELS IN FAIR AGREEMENT WITH QPF FORECAST THROUGH
THE FIRST 18 HOURS. PWS RISE FROM 1 IN TO NEAR 1.5 IN THE NORTHWEST
OVERNIGHT...WITH THE AXIS SHIFTING SOUTHEAST WITH THE FRONT. EXPECT
2 ROUNDS OF PRECIP...THE FIRST ONE WILL BE OVERNIGHT WITH AREAL
AVERAGES OF 1/10 TO 1/4 IN NORTHWEST AND AMOUNTS OF .01 TO .10
CENTRAL. THE SECOND ROUND OF PRECIP WILL COME TOMORROW AFTERNOON AS
THE FRONT STALLS OVER THE SOUTHERN THIRD OF THE STATE. WITH THIS
SCENARIO...WILL GO WITH THE AVN FOR THE LATTER PERIODS. GENERAL
AMOUNTS WILL AVERAGE .10 TO .20 INCH.

EXTENDED...CONTINUATION OF DRY AND WARM ON FRIDAY WITH NEXT CHANCE
OF RAIN SATURDAY AND SUNDAY AS NEXT SYSTEM BUCKS THE SOUTHEASTERN
RIDGE. WIDESPREAD PRECIP /IF ANY/ WOULD PROBABLY BE CONFINED TO THE
WESTERN PART OF OUR CWFA...WITH PRIMARY PRECIP MODE BEING AIRMASS
SHOWERS AND/OR THUNDERSTORMS.

.JAN...
MS...NONE.
AR...NONE.
LA...NONE.
06/22