SWODY1
SPC AC 111632
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1132 AM CDT WED APR 11 2007
VALID 111630Z - 121200Z
..THERE IS A SLGT RISK OF SVR TSTMS OH RIVER VALLEY...
..THERE IS A SLGT RISK OF SVR TSTMS GULF COAST STATES...
..MID SOUTH ACROSS THE OH RIVER VALLEY...
COMPLEX SCENARIO EXPECTED TO EVOLVE ACROSS THIS REGION TODAY WITHIN
EXIT REGION OF VERY STRONG MID AND UPPER LEVEL JET ASSOCIATED WITH
COMPACT UPPER LOW NOW OVER THE MID WEST. 15Z SURFACE ANALYSIS
INDICATES SURFACE LOW APPROACHING FAR SERN IA WITH WARM FRONT
EXTENDING ESEWD INTO SRN IND AND SRN OH...WHILE COLD FRONT TRAILS
SSWWD ALONG THE MS RIVER VALLEY. WELL DEFINED DRY SLOT AND STRONG
HEIGHT FALLS WILL OVERSPREAD THE NRN END OF THE WARM SECTOR DURING
THE AFTERNOON...INCREASING LOW TO MID LEVEL LAPSE RATES AND DEEP
ASCENT AHEAD OF THE COLD FRONT THROUGH THE EVENING. PRIMARY
QUESTION WILL CENTER ON QUALITY OF WARM SECTOR AIR MASS AS CURRENT
SURFACE DEW POINTS REMAIN AOB 50F OVER MUCH OF THE REGION. NARROW
AXIS OF LOWER TO MID 50F SURFACE DEW POINTS EXTENDS INTO FAR SERN IL
ATTM AND THIS SHOULD EXPAND NORTH AND NORTHEASTWARDS THROUGH THE
AFTERNOON. AXIS OF MARGINAL INSTABILITY IS THEREFORE EXPECTED TO
EVOLVE ALONG WRN EDGE OF LOW CLOUD DECK ACROSS THE LOWER OH RIVER
VALLEY EARLY THIS AFTERNOON...WITH SOME N-NWWD EXPANSION EXPECTED
INTO THE EARLY EVENING. MODELS ARE CONSISTENT IN INCREASING SHALLOW
MOIST CONVECTION ACROSS THIS REGION. GIVEN MAGNITUDE OF SHEAR AND
STEEPNESS OF LOW TO MID LEVEL LAPSE RATES...THE POTENTIAL FOR A FEW
SEVERE THUNDERSTORMS...INCLUDING LOW TOPPED SUPERCELLS...WILL
THEREFORE INCREASE. MARGINALLY SEVERE HAIL...ALONG WITH ISOLATED
DAMAGING WINDS AND PERHAPS A TORNADO OR TWO...CAN BE EXPECTED WITH
THE STRONGER CORES.
..TN VALLEY ACROSS THE SRN APPALACHIANS INTO THE SOUTHEAST...
SURFACE FEATURES REMAIN COMPLICATED ACROSS THIS REGION...THOUGH
SURFACE COLD FRONT IS WELL DEFINED ON SURFACE ANALYSES AND VISIBLE
IMAGERY MOVING INTO NWRN MS INTO CENTRAL LA LATE THIS MORNING.
SKIES CONTINUE TO CLEAR IN WAKE OF GRAVITY WAVE NOW PUSHING EWD AND
DISSIPATING OVER NRN GA/CENTRAL AL/FAR SRN MS...WITH HEATING
EXPECTED TO DIMINISH CAPPING AHEAD OF SURFACE COLD FRONT. EWD
EXPANSION OF MODEST INSTABILITY WILL REMAIN HAMPERED FOR MUCH OF THE
DAY ACROSS AL...THOUGH GRADUAL BREAKS IN CLOUDS SHOULD ALLOW BROADER
AREA OF INSTABILITY TO DEVELOP. REGION WILL REMAIN IN AREA OF
LIMITED OR NO DEEP ASCENT SOUTH OF UPPER JET AND STRONGER HEIGHT
FALLS OVERSPREADING THE OH RIVER VALLEY. IN ADDITION...LOW LEVEL
FLOW WILL CONTINUE TO VEER AS STRONG SSWLY LLJ LIFTS AWAY FROM THE
REGION. HOWEVER...HEATING AND SUFFICIENT SHEAR WILL REMAIN IN PLACE
AND SUPPORT AT LEAST A THREAT OF DEEP MOIST CONVECTION AND POSSIBLY
LINES/SUPERCELLS INTO THE EARLY EVENING. ACTUAL EVOLUTION OF
SCENARIO DIFFICULT TO PIN-DOWN AT THIS TIME GIVEN PRESENCE OF
SEVERAL BOUNDARIES TO FOCUS THUNDERSTORM DEVELOPMENT...THOUGH
CONDITIONAL SEVERE RISKS REMAIN WARRANTED.
MAY SEE A RELATIVE MINIMUM IN SEVERE THUNDERSTORM RISK ACROSS MIDDLE
TN INTO PORTIONS OF KY...BETWEEN CURRENT CATEGORICAL SLGT RISK
AREAS. THOUGH MARGINAL SEVERE THREAT MAY DEVELOP ACROSS THIS
REGION...STRONGER ASCENT WILL DEVELOP NWD AND GREATER HEATING WILL
REMAIN TO THE SOUTH.
.EVANS/GRAMS.. 04/11/2007
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