SWODY1
SPC AC 281629
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT WED SEP 28 2011
VALID 281630Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR SE
TX...SRN LA...SRN MS...
...SYNOPSIS...
THE LINGERING CLOSED LOW OVER THE UPPER MIDWEST IS BEGINNING TO MOVE
EWD IN RESPONSE TO UPSTREAM HEIGHT FALLS WITH A SHORTWAVE TROUGH
THAT WILL DIG SEWD FROM THE MT/SK BORDER TO THE UPPER MS VALLEY BY
EARLY THURSDAY. A SURFACE REFLECTION OF THE MIDLEVEL LOW WILL
WEAKEN SLOWLY OVER LOWER MI TODAY INTO TONIGHT...WHILE SEPARATE WEAK
CYCLOGENESIS IS EXPECTED ALONG THE SURFACE COLD JUST E OF THE
CENTRAL APPALACHIANS. THE TRAILING FRONT EXTENDS SWWD ACROSS THE
PIEDMONT TO THE GULF COAST STATES BETWEEN I-20 AND I-10.
...SE TX/SRN LA/SRN MS THROUGH LATE AFTERNOON...
STRONG SURFACE HEATING WITHIN A MOIST BOUNDARY LAYER...AND BENEATH
STEEP MIDLEVEL LAPSE RATES...WILL SUPPORT AFTERNOON MLCAPE VALUES OF
3000-4000 J/KG. THOUGH DEEP-LAYER VERTICAL SHEAR WILL REMAIN
RELATIVELY WEAK ALONG AND S OF THE FRONT /WELL S OF THE UPPER
MIDWEST CLOSED LOW/...THE STRONG INSTABILITY WILL SUPPORT A RISK FOR
MULTICELL CLUSTERS CAPABLE OF PRODUCING DAMAGING WINDS AND LARGE
HAIL. ASCENT PRECEDING A WEAK SHORTWAVE TROUGH NOW OVER SE OK/NE TX
WILL SPREAD SEWD TO NEAR THE STALLED FRONT IN SE TX/LA BY THIS
EVENING....THOUGH SURFACE HEATING/MIXING WILL BE THE PRIMARY
CONTRIBUTOR TO STORM DEVELOPMENT THIS AFTERNOON/EVENING.
...VA/MD/PA THIS AFTERNOON...
THE MIDWEST CLOSED LOW WILL DRIFT EWD TODAY...BUT THE STRONGER
MID-UPPER SWLY/SLY FLOW ALOFT AND ASSOCIATED VERTICAL SHEAR WILL
REMAIN LARGELY W OF THE MOIST WARM SECTOR IN VA/MD/PA.
MEANWHILE...REGIONAL 12Z SOUNDINGS SHOWED MOIST PROFILES AND RATHER
POOR MIDLEVEL LAPSE RATES...WHICH WILL KEEP AFTERNOON MLCAPE IN THE
1000-1500 J/KG RANGE. GIVEN THE LAPSE RATE PROFILES AND EFFECTIVE
BULK SHEAR GENERALLY AOB 30 KT IN THE CORRIDOR OF THE STRONGER
INSTABILITY...THE RISK FOR ORGANIZED SEVERE STORMS APPEARS MARGINAL
THIS AFTERNOON...AND ONLY LOW WIND/TORNADO PROBABILITIES APPEAR
WARRANTED.
..THOMPSON/GARNER.. 09/28/2011
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