SWODY1
SPC AC 271952
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0252 PM CDT TUE SEP 27 2011
VALID 272000Z - 281200Z
...NO SVR TSTM AREAS FORECAST...
.CHANGE TO PREV OTLK...
1. ADJUST LOW SVR PROBABILITIES ACROSS THE SERN STATES
...SERN STATES...
HAVE ADJUSTED LOW SVR WIND PROBABILITIES A LITTLE FARTHER NEWD
ACROSS CNTRL GA AND CNTRL SC ALONG A WEAK WIND SHIFT WHERE A FEW
TSTMS HAVE DEVELOPED THIS AFTN. ACTIVITY APPEARS TO BE RESPONDING
TO BOTH ENHANCED THERMAL BUOYANCY AND THE APPROACHING UPR LVL
DISTURBANCE ROTATING THROUGH SCNTRL AL. ENVIRONMENT CONSISTING OF
MLCAPE TO 2500 J/KG AND STEEP LLVL LAPSE RATES WILL MAINTAIN AN
ISOLD THREAT FOR DMGG WINDS/HAIL WITH MULTICELL STORM CLUSTERS.
OTHERWISE...WEAK VERTICAL SHEAR WILL LIMIT OVERALL STORM
ORGANIZATION.
REMAINDER OF PREV FCST UNCHANGED.
..RACY.. 09/27/2011
.PREV DISCUSSION... /ISSUED 1118 AM CDT TUE SEP 27 2011/
...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.
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