SWODY1
SPC AC 221249
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0649 AM CST TUE NOV 22 2011
VALID 221300Z - 231200Z
...THERE IS A SLGT RISK OF SVR TSTMS THROUGH TONIGHT FOR THE LOWER
MS/TN/OH VALLEY REGION...
...LOWER MS/TN/OH VALLEY REGION THROUGH EARLY TONIGHT...
A POSITIVELY-TILTED MIDLEVEL TROUGH FROM N TX TO MO WILL PROGRESS
EWD TO THE OH/TN VALLEYS THIS EVENING AND THE APPALACHIANS BY
WEDNESDAY MORNING. AN ASSOCIATED SURFACE CYCLONE NEAR THE MO
BOOTHEEL WILL DEVELOP NEWD IN ADVANCE OF THE MIDLEVEL TROUGH...ALONG
A PRE-EXISTING FRONT ALIGNED NEAR THE OH RIVER. A TRAILING COLD
FRONT WILL MOVE SEWD ACROSS TX AND THE LOWER MS/TN VALLEYS THROUGH
TONIGHT.
THE STRONGER FORCING FOR ASCENT AND VERTICAL SHEAR TODAY WILL BE
DISPLACED TO THE N OF THE MORE UNSTABLE WARM SECTOR CLOSER TO THE
GULF COAST. RAIN AND EMBEDDED THUNDERSTORMS HAVE ALREADY SPREAD
EWD/NEWD INTO WRN TN/KY IN ADVANCE OF THE SURFACE LOW...WHERE
BOUNDARY LAYER DEWPOINTS ARE UNLIKELY TO EXCEED THE LOWER 60S AND
WARM SECTOR DESTABILIZATION IS IN QUESTION. FARTHER S/SW...A
MARITIME TROPICAL AIR MASS HAS PENETRATED INLAND ACROSS SE TX AND
SRN LA...AND 66-70 F DEWPOINTS WILL LIKELY MOVE INLAND TODAY ACROSS
MS/AL IN ADVANCE OF THE COLD FRONT AND PRE-FRONTAL SQUALL LINE.
MODEST MIDLEVEL LAPSE RATES AND SURFACE HEATING AHEAD OF THE
CONVECTIVE BAND WILL SUPPORT MLCAPE OF 1000-1500 J/KG GENERALLY S OF
I-20 THIS AFTERNOON...WITH MLCAPE DECREASING TO A FEW HUNDRED J/KG
CLOSER TO THE SURFACE CYCLONE ACROSS KY/SE INDIANA/SRN OH.
CONVECTION ACROSS WRN TN/NW MS/NRN LA EARLY THIS MORNING HAS
PROGRESSED ABOUT 50-100 MI AHEAD OF THE SURFACE COLD FRONT.
ADDITIONAL DESTABILIZATION TODAY BEHIND THIS BAND IS UNLIKELY GIVEN
THE THICK CLOUDS AND DEEP-LAYER PROFILE CHANGES NOTED AT SHV AND LZK
WITH PASSAGE OF THE STORMS. FARTHER SW...THE STORMS SHOULD REMAIN
MORE CLOSELY TIED TO THE FRONT ACROSS SE TX. LATER THIS MORNING AND
INTO THIS AFTERNOON...SOME INTENSIFICATION OF STORMS IS EXPECTED IN
A BROKEN BAND NEAR THE LEADING EDGE OF THE REMNANT PRE-FRONTAL LINE
ACROSS LA/MS...AND THE STORMS WILL SUBSEQUENTLY SPREAD EWD INTO AL.
SOMEWHAT UNIDIRECTIONAL WIND PROFILES BY AFTERNOON SUGGEST THAT
DAMAGING WINDS WITH LINE SEGMENTS WILL BE THE MAIN SEVERE STORM
THREAT. LOW-LEVEL SHEAR WILL BE STRONG ENOUGH IN THE MOIST
ENVIRONMENT TO SUPPORT THE RISK OF A TORNADO OR TWO WITH EMBEDDED
QLCS CIRCULATIONS...OR WITH ANY ISOLATED/DISCRETE STORMS THAT MANAGE
TO DEVELOP AHEAD OF THE LINE.
...E OF CENTRAL/SRN APPALACHIANS AFTER ABOUT 06Z...
THE COLD FRONT AND ASSOCIATED FRONTAL CONVECTION ARE NOT EXPECTED TO
REACH E OF THE APPALACHIANS UNTIL ROUGHLY 06Z. THOUGH INSTABILITY
WILL BE WEAK FROM SC NWD INTO VA...A GRADUAL INCREASE IN LOW-LEVEL
MOISTURE WILL ALLOW MUCAPE OF 250-500 J/KG ROOTED NEAR THE SURFACE.
DESPITE THE WEAK INSTABILITY AND A SHALLOW STABLE LAYER NEAR THE
GROUND...A STRONG LOW-MIDLEVEL VERTICAL SHEAR ENVIRONMENT EXPECTED
IN ADVANCE OF THE FRONT WILL SUPPORT A RISK FOR ISOLATED
STRONG/DAMAGING GUSTS.
..THOMPSON/JIRAK.. 11/22/2011
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