SWODY1
SPC AC 271618
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1118 AM CDT TUE SEP 27 2011
VALID 271630Z - 281200Z
...NO SVR TSTM AREAS FORECAST...
...NC TO PA THIS AFTERNOON/EVENING...
THE OCCLUDED DEEP-LAYER CYCLONE OVER NE IL/NW INDIANA THIS MORNING
WILL DRIFT EWD AND WEAKEN THROUGH TONIGHT. FARTHER E AND S...A
SLOW-MOVING FRONT WILL REMAIN FROM NEAR THE E SLOPES OF THE
APPALACHIANS SWWD AND WWD ALONG THE I-20 CORRIDOR INTO NE TX. WEAK
SPEED MAXIMA WILL CONTINUE TO ROTATE AROUND THE MIDLEVEL LOW...AND
THE ERN FRINGE OF THE STRONGER MID-UPPER SWLY/SLY FLOW WILL BE
MAINTAINED NEAR THE APPALACHIANS. BOUNDARY LAYER DEWPOINTS OF 68-72
F AND MOIST PROFILES WILL SUPPORT A CONTINUED RISK OF THUNDERSTORMS
THROUGH THE PERIOD ALONG AND E OF THE SURFACE FRONT.
HOWEVER...CLOUDS WILL LIMIT SURFACE HEATING FROM NRN VA INTO
PA...AND LOW-MIDLEVEL VERTICAL SHEAR WILL NOT BE PARTICULARLY STRONG
IN THE WARM SECTOR. THUS...WHILE A FEW DAMAGING GUSTS WILL BE
POSSIBLE WITH THE STRONGER MULTICELL CLUSTERS...THE OVERALL SEVERE
STORM RISK APPEARS TOO MARGINAL TO WARRANT A CATEGORICAL UPGRADE.
...SE AL/FL PANHANDLE/SW GA THIS AFTERNOON...
AN OUTFLOW BOUNDARY EMANATING FROM OVERNIGHT CONVECTION HAS RECENTLY
CONTRIBUTED TO NEW THUNDERSTORM DEVELOPMENT ACROSS S CENTRAL/SE AL.
MODERATE INSTABILITY IS EXPECTED IN ADVANCE OF THESE DEVELOPING
STORMS AS A RESULT OF STRONG SURFACE HEATING...WHICH WILL SUPPORT AN
INCREASE IN STORM COVERAGE/INTENSITY. THOUGH VERTICAL SHEAR IS
WEAK...THE STRONGER MULTICELL STORMS WILL BE CAPABLE OF PRODUCING
ISOLATED STRONG/DAMAGING OUTFLOW GUSTS THIS AFTERNOON.
...CENTRAL TX THIS AFTERNOON/EVENING...
THE SURFACE FRONT HAS STALLED A LITTLE S OF I-20 IN NE AND CENTRAL
TX. 12Z SOUNDINGS REVEALED A STRONG CAP AT THE BASE OF A WARM
ELEVATED MIXED LAYER...AND THE POTENTIAL FOR STRONG INSTABILITY THIS
AFTERNOON. ANOTHER DAY OF INTENSE SURFACE HEATING/
MIXING...COMBINED WITH SHALLOW ASCENT ALONG THE FRONT AND A WEAK
MIDLEVEL WAVE OVER CENTRAL TX...SHOULD PROMOTE THUNDERSTORM
DEVELOPMENT LATER THIS AFTERNOON. VERTICAL SHEAR WILL BE RELATIVELY
WEAK...BUT 2000-3000 J/KG MLCAPE AND STEEP LOW-LEVEL LAPSE RATES
WILL SUPPORT HYBRID DOWNBURSTS AND A RISK FOR AT LEAST ISOLATED
DAMAGING WINDS.
..THOMPSON/HURLBUT.. 09/27/2011
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