SWODY3
SPC AC 040826
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0226 AM CST TUE NOV 04 2008
VALID 061200Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS THU ACROSS THE LOWER HALF OF
THE MISSISSIPPI VALLEY....
...SYNOPSIS...
THE SPREAD AMONG MODELS AND NCEP SREF/MREF MEMBERS CONCERNING THE
LARGE-SCALE FLOW EVOLUTION BEGINS TO GROW DURING THIS FORECAST
PERIOD. BUT...IT APPEARS THAT THE EASTWARD PROGRESSION OF THE
AMPLIFIED POLAR TROUGH ACROSS THE PLAINS/MISSISSIPPI VALLEY WILL
SLOW DURING THIS PERIOD. AND...THE LOW/MID LEVEL CYCLONE WITHIN THE
SOUTHERN BRANCH OF SPLIT DOWNSTREAM WESTERLIES WILL BE SLOW TO SHIFT
AWAY FROM THE MID ATLANTIC COAST.
...MISSISSIPPI VALLEY...
WITHIN THE MAIN POLAR TROUGH...THE PRIMARY EMBEDDED SHORT WAVE
IMPULSE IS EXPECTED TO CONTINUE PIVOTING AROUND THE EASTERN/
NORTHERN PERIPHERY OF THE DEEP LOW/MID-LEVEL CLOSED LOW OVER THE
UPPER MISSISSIPPI VALLEY...AND THE CYCLONE WILL LIKELY GRADUALLY
OCCLUDE. ALTHOUGH MEAN DEEP LAYER WIND FIELDS AND SHEAR WILL REMAIN
SUFFICIENT FOR SEVERE STORMS OVER A BROAD AREA OF THE CENTRAL
U.S....BOUNDARY LAYER INSTABILITY ASSOCIATED WITH THE MOIST WARM
SECTOR SHOULD BECOME CONFINED TO A SHRINKING WEDGE ACROSS THE LOWER
MISSISSIPPI VALLEY AND WESTERN GULF COAST REGION.
THUS...IT CURRENTLY APPEARS THAT THE SEVERE THREAT ACCOMPANYING A
WEAKENING PRE-FRONTAL CONVECTIVE BAND WILL DIMINISH EARLY THURSDAY
ACROSS THE MID AND UPPER MISSISSIPPI VALLEY.
FARTHER SOUTH...HOWEVER...LOW-LEVEL MOISTURE MAY CONTINUE TO
INCREASE IN THE WARM SECTOR UNTIL THE GULF RETURN FLOW BECOMES CUT
OFF LATE THURSDAY/THURSDAY NIGHT. WHILE STRONGER MID-LEVEL COOLING
ASSOCIATED WITH THE NEXT IMPULSE DIGGING AROUND THE CLOSED MID/UPPER
LOW IS PROGGED TO REMAIN WELL TO THE NORTHWEST OF THE LOWER
MISSISSIPPI VALLEY...INCREASINGLY DIFLUENT AND DIVERGENT UPPER FLOW
COUPLED WITH FRONTAL FORCING MAY BE SUFFICIENT TO SUPPORT A BROKEN
LINE OF STORMS THURSDAY AFTERNOON. IN THE PRESENCE OF WEAK TO
MODERATE INSTABILITY AND FAVORABLE DEEP LAYER SHEAR BENEATH 30-50 KT
CYCLONIC 500 MB FLOW...STRONGER CONVECTION MAY BE CAPABLE OF
PRODUCING DAMAGING WINDS AND HAIL BEFORE WEAKENING DURING THE
EVENING HOURS.
..KERR.. 11/04/2008
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