SWODY1
SPC AC 181235
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0735 AM CDT WED MAR 18 2009
VALID 181300Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A MID LEVEL LOW OVER JAMES BAY WILL PROGRESS EWD OVER QUEBEC WHILE A
TRAILING SHORTWAVE TROUGH AMPLIFIES SLIGHTLY OVER THE UPPER GREAT
LAKES THROUGH EARLY THURSDAY. IN ASSOCIATION WITH THIS MID LEVEL
TROUGH...A SURFACE COLD FRONT WILL MOVE SEWD ACROSS THE SRN PLAINS
AND MID MS/OH VALLEYS. THIS COLD FRONT WILL PROVIDE THE PRIMARY
FOCUS FOR THUNDERSTORM DEVELOPMENT THIS AFTERNOON INTO TONIGHT.
ELSEWHERE...MOIST PROFILES BELOW 500 MB AND MARGINAL INSTABILITY
WILL SUPPORT WARM PROCESS SHOWERS /AND PERHAPS ISOLATED LIGHTNING
STRIKES WITH THE DEEPER CONVECTIVE ELEMENTS/...IN ADVANCE OF A WEAK
SRN STREAM TROUGH OVER THE ERN GULF OF MEXICO.
...SW INDIANA/SRN IL/SRN MO THIS AFTERNOON INTO EARLY TONIGHT...
STRONG SURFACE HEATING /AFTERNOON TEMPERATURES INTO THE 70S/ AND
NEWD ADVECTION OF 48-50 F BOUNDARY LAYER DEWPOINTS FROM OK...BENEATH
7-8 C/KM MID LEVEL LAPSE RATES AND COOL MID LEVEL TEMPERATURES...
WILL RESULT IN A NARROW BELT OF MLCAPE NEAR 500 J/KG THIS
AFTERNOON/EVENING ALONG THE COLD FRONT. THE REDUCTION IN CONVECTIVE
INHIBITION THROUGH SURFACE HEATING/MIXING...AND LOW-LEVEL ASCENT
ALONG THE FRONT...WILL SUPPORT A BROKEN BAND OF THUNDERSTORMS ALONG
THE FRONT BEGINNING 21-00Z. CONVECTION WILL LIKELY BUILD WSWWD
ACROSS SRN MO AND POTENTIALLY AS FAR SW AS N/NE OK OVERNIGHT...ON
THE IMMEDIATE COOL SIDE OF THE BOUNDARY. THE DEGREE OF INSTABILITY
AND COOL MID LEVEL TEMPERATURES APPEAR SUFFICIENT FOR AT LEAST
ISOLATED MARGINALLY SEVERE HAIL AND GUSTY DOWNBURST WINDS IN THE
21-03Z PERIOD. THE OVERALL MAGNITUDE OF THE SEVERE THREAT WILL BE
LIMITED...HOWEVER...BY GRADUAL STABILIZATION AFTER SUNSET AND ONLY
MARGINAL WARM SECTOR VERTICAL SHEAR /S OF THE MAIN BELT OF MID-UPPER
WESTERLIES/.
..THOMPSON/GRAMS.. 03/18/2009
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