SPC AC 111953
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0153 PM CST SAT DEC 11 2010
VALID 112000Z - 121200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE LOWER MS
VALLEY AND CENTRAL GULF COAST REGION...
PREVIOUS FORECAST LOOKS ON TRACK. THICKENING MID/HIGH LEVEL CLOUDS
OVER THE SRN ARKLATEX APPEAR TO BE TIED TO INCREASING UPPER LEVEL
DIFFLUENCE SPREADING ENEWD AHEAD OF 90-100 KT UPPER JET MAX. STORM
SCALE AND OPERATIONAL MODELS ALL IN AGREEMENT OF THUNDERSTORMS
DEVELOPING SOON NEAR/AHEAD OF FRONT ACROSS SERN AR/NERN LA...AS
FORCING/FRONT AND MUCAPES TO 500 J/KG BECOME ALIGNED. THIS MAY
EVOLVE AS BAND OF MID LEVEL CONVECTION...BETWEEN SHV/MLU NEWD TOWARD
MEM...GRADUALLY STRENGTHENS.
GIVEN THE RAPID MOVEMENT OF THE SURFACE FRONT/JET MAX...STORMS
LIKELY TO BECOME LINEAR SHORTLY AFTER THEY DEVELOP. THE MEAN FLOW
WILL SHIFT THE STORMS/LINE EWD...THOUGH CONVECTION SHOULD DECREASE
FROM THE NORTH AS THE STORMS ENCOUNTER PROGRESSIVELY LESS
INSTABILITY TO THE EAST. THIS SHOULD RESULT IN STRONGER CONVECTION
SHIFTING/DEVELOPING SEWD INTO CENTRAL/SRN MS BY LATE AFTERNOON AND
INTO WRN AL THIS EVENING. WIND DAMAGE SHOULD BE THE PRIMARY THREAT
GIVEN THE STRONG ENVIRONMENTAL WINDS AND FAST MOVING LINE.
HOWEVER...AROUND 30 KT OF LOW LEVEL SHEAR AND LOWERING LCL HEIGHTS
INDICATE A TORNADO OR TWO IS POSSIBLE...ESPECIALLY IF EMBEDDED
STORMS WITHIN THE LINE CAN BECOME SEMI-DISCRETE.
THE EARLIER THUNDER IN MO...ASSOCIATED WITH LOW/MID LEVEL WARM
ADVECTION...HAS WEAKENED AND SHIFTED NEWD INTO IL/KY. THUS..THE MAIN
GRAPHICAL CHANGE TO THE OUTLOOK WAS TO TRIM THE NRN END OF THE
THUNDER LINE.
..IMY.. 12/11/2010
.PREV DISCUSSION... /ISSUED 1005 AM CST SAT DEC 11 2010/
...LOWER MS VALLEY...
STRONG DEEPENING OF UPPER LOW UNDERWAY CENTRAL U.S. WITH CENTER OF
CIRCULATION BY 12Z SUNDAY OVER LOWER OH VALLEY. ASSOCIATED SURFACE
LOW OVER IA WITH COLD FRONT TRAILING SWWD THIS MORNING ACROSS ERN OK
INTO NRN TX. LOW CONTINUES EWD AS STRONG COLD FRONT SWEEPS SEWD
REACHING GULF STATES AND OFF THE TX COAST LATER TONIGHT.
AIR MASS RETURNING FROM GULF AHEAD OF FRONT INTO LOWER MS VALLEY IS
MODIFIED POLAR WITH LIMITED POTENTIAL FOR DEVELOPING INSTABILITY
PRIOR TO COLD FROPA. INITIALLY ELEVATED MIXED LAYER SPREADING EWD
ACROSS S TX WILL CAP THE WARM SECTOR. HOWEVER WITH LARGE SCALE
ASCENT AND SURFACE HEATING OF THE LOW LEVEL AIR MASS...NAM FORECAST
OF MLCAPES TO AOA 500 J/KG AND WEAKENING CAP DO SUPPORT A WINDOW OF
OPPORTUNITY OF LOW TOPPED CONVECTION DEVELOPING IN THE PRE-FRONTAL
CONVERGENCE THAT SETS UP FROM CENTRAL LA INTO SWRN MS THIS
AFTERNOON.
THE PRIMARY SEVERE THREAT APPEARS TO STILL BE WIND ASSOCIATED WITH
THE FORCED THUNDERSTORM DEVELOPMENT WITH THE COLD FRONTAL
CONVERGENCE LATER THIS AFTERNOON AND EVENING. HOWEVER HAVE RAISED
THE TORNADO POTENTIAL TO 5 PERCENT STRADDLING THE MS RIVER IN WRN
MS/ERN LA FOR THE INCREASED THREAT OF MORE DISCRETE LOW TOPPED
THUNDERSTORM DEVELOPMENT IN REGION OF EXPECTED GREATEST INSTABILITY.
THIS ENVIRONMENT WILL BE FAVORABLE FOR SUPERCELLS AS SRH WILL
INCREASE TO 300 J/KG WITH APPROACH OF THE STRONG MID/UPPER JET
ROTATING AROUND DEEPENING UPPER LOW TO THE N COUPLED WITH THE
40-50KT LOW LEVEL JET IN THE WARM SECTOR.
A THREAT OF STRONG/ISOLATED DAMAGING WINDS WILL PERSIST WITH THE
LINE OF THUNDERSTORMS ALONG THE COLD FRONT THROUGH THE EVENING AS IT
MOVES SEWD. WHILE THE WARM SECTOR WILL BECOME INCREASINGLY HOSTILE
TO DEEP CONVECTION...THE DEEPENING UPPER LOW TO THE N AND THE 100 KT
500MB JET ROTATING ACROSS THE GULF STATES...SUPPORTS AT LEAST A LOW
END THREAT OF DAMAGING WINDS SEWD TO SWRN AL/WRN FL PANHANDLE
TONIGHT.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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