SWODY1
SPC AC 211221
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0721 AM CDT SAT APR 21 2012
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATER TODAY INTO EARLY SUNDAY
ACROSS THE CNTRL/SRN FL PENINSULA...
...SYNOPSIS...
MID AND UPPER-LEVEL JET STREAKS FROM THE NRN HIGH PLAINS INTO MID-MO
VALLEY WILL DIG SEWD TOWARD THE CONFLUENCE OF THE MS AND OH
RIVERS...CONTRIBUTING TO INTENSIFICATION OF MIDLEVEL TROUGH FROM THE
GREAT LAKES INTO TN VALLEY. THIS PATTERN EVOLUTION WILL HASTEN THE
EWD PROGRESSION OF UPPER LOW /CURRENTLY OFF THE LA COAST/ ACROSS THE
CNTRL/ERN GOM BEFORE TURNING MORE NEWD ACROSS THE FL PENINSULA LATE
TONIGHT INTO SUNDAY MORNING. ELSEWHERE...A SHORTWAVE TROUGH OVER
IL/IND INTO WRN PARTS OF KY/TN WILL WEAKEN TODAY WHILE PROGRESSING
ENEWD INTO THE NRN/CNTRL APPALACHIANS.
IN THE LOW LEVELS...BROAD LOW PRESSURE FROM SERN LA INTO THE CNTRL
GOM WILL CONSOLIDATE TODAY OVER THE ERN GULF BASIN WITH THIS FEATURE
TRACKING ACROSS THE NRN OR CNTRL FL PENINSULA TONIGHT...TO OFF THE
NERN FL COAST BY 22/12Z. THIS LOW PRESSURE WILL LINK WITH A COLD
FRONT ADVANCING EWD ACROSS THE NERN AND MID-ATLANTIC STATES.
...FL LATER TODAY INTO EARLY SUNDAY...
THE LOW-LATITUDE NATURE OF UPPER SYSTEM WILL MAINTAIN A FEED OF VERY
MOIST AIR FROM THE CARIBBEAN ACROSS PRE-FRONTAL WARM SECTOR WHERE
BOUNDARY LAYER DEWPOINTS WILL RANGE FROM THE MID 60S TO LOWER 70S.
HOWEVER...WIDESPREAD CLOUDS AND EPISODIC TSTM ACTIVITY WILL LIMIT
AIR MASS DESTABILIZATION WITH MLCAPE VALUES LIKELY REMAINING BELOW
1000-1500 J/KG.
WHILE ISOLATED SEVERE STORMS CAPABLE OF LOCALLY DAMAGING WINDS AND
PERHAPS A TORNADO WILL BE POSSIBLE TODAY...IT APPEARS THAT A
POTENTIALLY MORE SUBSTANTIAL SEVERE WEATHER THREAT WILL NOT
MATERIALIZE UNTIL THIS EVENING INTO TONIGHT. AT THIS TIME...BOTH
FORCING FOR ASCENT AND VERTICAL SHEAR WILL STRENGTHEN MARKEDLY IN
ADVANCE OF DEEP-LAYER CYCLONE OVER THE ERN GOM. THE SEVERE WEATHER
THREAT WILL BE MODULATED BY THE AMOUNT OF ANTECEDENT TSTM ACTIVITY
AND IT/S IMPACTS ON AIR MASS DESTABILIZATION. GIVEN SUFFICIENT
INSTABILITY...THE LARGE-SCALE PATTERN WILL BE SUPPORTIVE OF
SUPERCELLS AND BOWING STRUCTURES WITH AN ASSOCIATED RISK FOR
TORNADOES AND DAMAGING WINDS INTO EARLY SUNDAY.
...NEW ENGLAND INTO MID-ATLANTIC STATES TODAY...
VISIBLE SATELLITE IMAGERY SHOWS CLOUD BREAKS ACROSS PRE-FRONTAL AIR
MASS WHICH SHOULD ALLOW FOR POCKETS OF LOCALLY STRONG DIABATIC
WARMING AND A RESULTANT STEEPENING OF LOW-LEVEL LAPSE RATES.
HOWEVER...BOUNDARY LAYER WILL BE ONLY MARGINALLY MOIST WITH
DEWPOINTS IN THE LOWER-MID 50S. WHEN COUPLED WITH WEAK MIDLEVEL
LAPSE RATES...ENVIRONMENT IS EXPECTED TO BECOME ONLY MARGINALLY
UNSTABLE THIS AFTERNOON WITH MLCAPE REMAINING GENERALLY BELOW
500-1000 J/KG.
ENTRANCE REGION OF MID AND UPPER-LEVEL JET STREAKS WILL RESIDE ALONG
COLD FRONT TODAY...ENHANCING THE STRENGTH OF DEEP-LAYER WIND FIELD
AND VERTICAL SHEAR. AS SUCH...THE POTENTIAL WILL EXIST FOR ISOLATED
SEVERE STORMS CAPABLE OF MAINLY DAMAGING WIND GUSTS. ORGANIZED
SEVERE WEATHER POTENTIAL IS EXPECTED TO BE LIMITED BY THE MARGINAL
INSTABILITY...THUS ONLY LOW WIND PROBABILITIES APPEAR WARRANTED.
..MEAD/LEITMAN.. 04/21/2012
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