SWODY1
SPC AC 121957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0157 PM CST WED NOV 12 2008
VALID 122000Z - 131200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
SUBSTANTIVE LOW-LEVEL MOISTURE RETURN OFF THE GULF OF MEXICO AND
WESTERN ATLANTIC IS NOW UNDERWAY EAST OF THE MISSISSIPPI VALLEY.
BUT...THIS IS OCCURRING FASTER THAN THE RETREAT OF THE LARGE COLD
SURFACE RIDGE NEAR THE ATLANTIC SEABOARD. AS A RESULT...NORTHEAST
OF THE LOWER MISSISSIPPI VALLEY...THE MOISTURE IS GENERALLY BEING
LIFTED ABOVE A RESIDUAL STABLE SURFACE-BASED LAYER.
MEANWHILE...CLOUD COVER/PRECIPITATION ASSOCIATED WITH WEAKENING
OVERNIGHT STORMS HAS STABILIZED MUCH OF THE LOWER MISSISSIPPI VALLEY
INTO THE NORTHWEST GULF OF MEXICO. AND...BOUNDARY LAYER
DESTABILIZATION IS GENERALLY CONFINED TO AREAS SOUTH OF A DEVELOPING
SURFACE FRONT...ACROSS THE NORTHWESTERN GULF OF MEXICO...THROUGH
NORTHERN FLORIDA...INTO AREAS OFF THE SOUTH ATLANTIC COAST.
...LOWER MISSISSIPPI VALLEY THROUGH ATLANTIC SEABOARD...
IT SEEMS PROBABLE THAT SUBTROPICAL RIDGING WILL CAP THE UNSTABLE
BOUNDARY LAYER ACROSS THE NORTHEASTERN GULF OF MEXICO...THE FLORIDA
PENINSULA AND SOUTH ATLANTIC COASTAL AREAS. EVEN TO THE NORTH OF
THE FRONT...A RELATIVELY WARM MID-LEVEL ENVIRONMENT WITH WEAK LAPSE
RATES IS EXPECTED TO CONTINUE TO MINIMIZE CAPE...RESULTING IN LOW
AND UNCERTAIN THUNDERSTORM PROBABILITIES.
AS THE SURFACE RIDGE FINALLY RETREATS EAST OF THE ATLANTIC
COAST...AND AN UPSTREAM SHORT WAVE IMPULSE CONTINUES TO LIFT OUT OF
THE BASE OF THE SOUTH CENTRAL STATES SOUTHERN STREAM TROUGH...A
LOW-LEVEL BAROCLINIC ZONE IS PROGGED TO TIGHTEN TO THE LEE OF THE
SOUTHERN APPALACHIANS. MOISTURE RETURN AND STEEPENING ISENTROPIC
ASCENT NEAR THIS FEATURE BY LATE TONIGHT SEEMS TO OFFER THE BEST
POTENTIAL FOR SCATTERED THUNDERSTORM ACTIVITY. OTHERWISE...ENHANCED
LIFT ALONG THE WESTERN SLOPES OF THE SOUTHERN/CENTRAL APPALACHIANS
MAY SUPPORT SLIGHTLY HIGHER THUNDERSTORM PROBABILITIES THAN
CURRENTLY ANTICIPATED THIS EVENING ACROSS PARTS OF THE LOWER
OHIO/TENNESSEE VALLEYS.
...DEEP SOUTH TEXAS...
IN THE WAKE OF THE SOUTHERN STREAM SHORT WAVE IMPULSE LIFTING TOWARD
THE LOWER OHIO VALLEY...CONVECTIVE POTENTIAL HAS DIMINISHED ...WITH
THE STRONGER LOW-LEVEL FORCING NEAR A PRE-FRONTAL CONFLUENCE BAND
NOW OFFSHORE. HOWEVER...IT IS NOT YET ENTIRELY CLEAR THAT
ADDITIONAL STORM DEVELOPMENT WILL NOT OCCUR LATE TONIGHT AS THE NEXT
IMPULSE BEGINS TO SLOWLY APPROACH THE REGION. IF THIS OCCURS...IT
WILL LIKELY BE POST-FRONTAL...BUT ELEVATED INSTABILITY AND SHEAR
COULD BE SUFFICIENT FOR SEVERE STORMS CAPABLE OF PRODUCING LARGE
HAIL...PERHAPS STRONG WIND GUSTS. THE BEST CHANCE FOR VIGOROUS NEW
STORM DEVELOPMENT TONIGHT SEEMS TO BE IN ASSOCIATION WITH MOIST
UPSLOPE FLOW TO THE WEST OF THE RIO GRANDE VALLEY...AND IN THE
OFFSHORE UNSTABLE BOUNDARY LAYER.
..KERR.. 11/12/2008
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