SWODY1
SPC AC 191247
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0647 AM CST THU NOV 19 2009
VALID 191300Z - 201200Z
...NO SVR TSTM AREAS FORECAST...
...MID ATLANTIC REGION TODAY INTO TONIGHT...
THE CLOSED LOW OVER NW IL WILL GRADUALLY ACCELERATE AND MOVE ENEWD
TO THE LOWER GREAT LAKES BY EARLY FRIDAY...IN RESPONSE TO UPSTREAM
HEIGHT FALLS WITH A WEAKENING NRN STREAM SHORTWAVE TROUGH. SLOW
EROSION OF THE COOL AIR WEDGE E OF THE APPALACHIANS AND CONTINUED
MOISTURE INFLUX NEAR/ABOVE THE SURFACE WILL CONTRIBUTE TO SUFFICIENT
DESTABILIZATION FOR A FEW ELEVATED THUNDERSTORMS FROM VA NWD INTO
PA/NY/NJ. FARTHER S IN ERN NC...INSTABILITY WILL BE ROOTED AT OR
VERY NEAR THE SURFACE IN CONJUNCTION WITH BOUNDARY LAYER DEWPOINTS
IN THE MID 60S...THOUGH THE DEGREE OF SURFACE HEATING IS IN QUESTION
GIVEN WIDESPREAD CLOUDS OVER ERN NC. DEEP-LAYER AND LOW-LEVEL
VERTICAL SHEAR WILL BE MARGINALLY FAVORABLE FOR SUPERCELLS...THOUGH
PROFILES ARE NOT PARTICULARLY SUPPORTIVE OF DAMAGING WINDS AND/OR
LARGE HAIL.
...CENTRAL TX TO THE MIDDLE/LOWER TX COAST TONIGHT...
A SRN STREAM SHORTWAVE TROUGH WILL MOVE EWD OVER NRN MEXICO TO THE
TX BIG BEND REGION BY EARLY FRIDAY. IN ADVANCE OF THIS WAVE...A
MODIFYING AIR MASS WILL RETURN NWD/NWWD FROM THE WRN GULF OF MEXICO
TO S/CENTRAL TX...SE OF A DEVELOPING BAROCLINIC ZONE/INVERTED
TROUGH. THE COMBINATION OF LOW-LEVEL MOISTENING AND GRADUAL COOLING
ALOFT WILL SUPPORT MUCAPE VALUES OF 500-1250 J/KG /LARGEST NEAR THE
COAST/...THOUGH A STABLE LAYER FROM 850-700 MB WILL INHIBIT
CONVECTIVE INITIATION THROUGH MOST OF THE AFTERNOON. THE
ENVIRONMENT WILL BECOME INCREASINGLY FAVORABLE FOR THUNDERSTORM
DEVELOPMENT TONIGHT IN RESPONSE TO INCREASING DPVA AND WAA...AND A
LARGE THUNDERSTORM CLUSTER IS EXPECTED TO DEVELOP BY 06Z INVOF THE
MIDDLE TX COAST.
VERTICAL SHEAR WILL BE SUFFICIENT FOR EMBEDDED SUPERCELLS...
ESPECIALLY NEAR THE COAST WHERE THE MODEST INSTABILITY WILL BE
ROOTED AT THE SURFACE ALONG A DEVELOPING COASTAL TROUGH.
OTHERWISE...A MARGINAL HAIL THREAT WILL EXTEND FARTHER INLAND WITH
MORE ELEVATED CONVECTION OVERNIGHT. AT THIS TIME...THE SEVERE STORM
THREAT APPEARS TOO MARGINAL TO WARRANT MORE THAN LOW
PROBABILITIES...WHILE LOCALLY HEAVY RAINFALL WILL BE A GREATER
CONCERN LATER TONIGHT.
..THOMPSON/HURLBUT.. 11/19/2009
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