SWODY2
SPC AC 221712
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1212 PM CDT TUE SEP 22 2009
VALID 231200Z - 241200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A LARGE CLOSED LOW OVER THE INTERIOR OF THE U.S. APPEARS LIKELY TO
REMAIN CUT OFF FROM THE STRONGER WESTERLIES THROUGH THIS FORECAST
PERIOD. THE COOL CYCLONIC FLOW REGIME IS EXPECTED TO CONTINUE TO
ENCOMPASS MUCH OF THE CENTRAL/SOUTHERN PLAINS AND ROCKIES REGION.
AFTER DRIFTING BACK TOWARD THE CENTRAL ROCKIES...MODELS INDICATE
THAT THE EMBEDDED MID-LEVEL CIRCULATION CENTER MAY SUBTLY BEGIN
LIFTING NORTHEASTWARD ACROSS THE CENTRAL HIGH PLAINS LATE
WEDNESDAY/WEDNESDAY NIGHT...AS UPPER RIDGING OVER THE NORTHERN
INTERMOUNTAIN REGION/ROCKIES WEAKENS IN RESPONSE TO A POLAR SHORT
WAVE TROUGH LIFTING ACROSS THE CANADIAN ROCKIES. AT THE SAME
TIME...SHORT WAVE TROUGHS...PROGRESSING THROUGH A BROADER SCALE
DOWNSTREAM TROUGH OVER THE EASTERN CANADIAN PROVINCES...APPEAR
LIKELY TO BE ACCOMPANIED BY SIGNIFICANT LOW-LEVEL COOLING...THE
LEADING EDGE OF WHICH IS PROGGED TO BEGIN ADVANCING INTO THE
NORTHEAST STATES BY WEDNESDAY EVENING.
...CENTRAL/EASTERN U.S...
STABILIZATION ASSOCIATED WITH LOW-LEVEL COOLING AND DRYING IS
EXPECTED TO MINIMIZE CONVECTIVE POTENTIAL FOR WEDNESDAY BENEATH THE
MID-LEVEL COLD CORE OF THE PLAINS UPPER LOW. HIGHEST THUNDERSTORM
PROBABILITIES SEEM LIKELY TO REMAIN FOCUSED ALONG OR JUST AHEAD OF
THE RESIDUAL FRONTAL BOUNDARY ACROSS THE LOWER MISSISSIPPI
VALLEY...PERHAPS AS FAR NORTH AS THE LOWER OHIO VALLEY. THIS IS
WHERE A RIBBON OF HIGH MOISTURE CONTENT AIR WILL SUPPORT MODEST
POTENTIAL INSTABILITY WITH DAYTIME HEATING...WHILE WEAK MID-LEVEL
LAPSE RATES AND WEAK DEEP LAYER FLOW/SHEAR PROBABLY LIMIT
SIGNIFICANT CONVECTIVE HAZARDS TO HEAVY RAINFALL...PERHAPS FREQUENT
CLOUD TO GROUND LIGHTNING.
WEAK TO MODERATE DESTABILIZATION WITHIN A LINGERING MOIST
ENVIRONMENT ACROSS MUCH OF THE EAST IS ALSO EXPECTED TO BECOME
SUPPORTIVE OF THUNDERSTORMS ALONG COASTAL AND INTERIOR SOUTHERN
PORTIONS OF THE FLORIDA PENINSULA. ADDITIONAL SCATTERED
THUNDERSTORMS ARE POSSIBLE ALONG MIDDLE/SOUTHERN ATLANTIC COASTAL
AREAS...AND WITHIN A WEAKLY FORCED PRE-FRONTAL ENVIRONMENT ACROSS
PARTS OF THE UPPER OHIO VALLEY AND NORTH CENTRAL APPALACHIANS. IN
CLOSER PROXIMITY TO THE FRONT...WEAKER DESTABILIZATION AND THE
GENERALLY LATE SOUTHWARD ADVANCEMENT INTO NEW ENGLAND SEEM LIKELY TO
MINIMIZE CONVECTIVE POTENTIAL DESPITE THE DEVELOPMENT OF MORE
FAVORABLE FLOW FIELDS FOR STRONG/SEVERE STORMS.
..KERR.. 09/22/2009
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