SPC AC 230640
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0140 AM CDT WED SEP 23 2009
VALID 251200Z - 261200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
23/00Z MODEL GUIDANCE IS IN GOOD AGREEMENT IN THE EWD PROGRESSION OF
UPPER LOW FROM THE CNTRL PLAINS INTO THE MID MO VALLEY. AS THIS
OCCURS...A BELT OF 50+ KT MIDLEVEL FLOW WILL DEVELOP EWD THROUGH THE
MID MS INTO OH VALLEY. AT THE SURFACE...LOW PRESSURE WILL
CONSOLIDATE OVER NEB BEFORE SHIFTING EWD INTO IA. FARTHER E...A
WARM FRONT WILL INTENSIFY WHILE LIFTING NWD THROUGH THE OH VALLEY.
HOWEVER...THE WIDTH OF DEVELOPING WARM SECTOR WILL BE MODULATED BY
SWD-BUILDING SURFACE RIDGE AXIS E OF THE APPALACHIANS.
...CNTRL PLAINS...
AS MENTIONED ABOVE...PRIMARY SYNOPTIC-SCALE WARM SECTOR WILL BE
DISPLACED TO THE E...ALONG AND E OF THE MID/LOWER MS VALLEY.
HOWEVER...THE COMBINATION OF DAYTIME HEATING AND PRESENCE OF
MIDLEVEL COLD POOL /-18 TO -20 C AT 500 MB/ WILL SUPPORT THE
DEVELOPMENT OF WEAK TO POTENTIALLY MODERATE CONVECTIVE INSTABILITY
BY AFTERNOON AHEAD OF SURFACE LOW AND TRAILING TROUGH/FRONT. THESE
SURFACE FEATURES WILL LIKELY SERVE AS THE FOCI FOR DIURNAL STORM
DEVELOPMENT WITHIN ZONE OF DEEP ASCENT ASSOCIATED WITH UPPER SYSTEM.
WHILE PRIMARY SEVERE THREAT WILL BE HAIL...SOME POTENTIAL WILL EXIST
FOR A TORNADO OR TWO NEAR SURFACE LOW WHERE STRONG...AMBIENT
VERTICAL VORTICITY WILL BE COLLOCATED WITH STEEP LAPSE RATES AND
LOCALLY BACKED LOW-LEVEL WINDS.
SHOULD LATER MODEL RUNS INDICATE STRONGER INSTABILITY...A
CATEGORICAL SLIGHT RISK WILL BE REQUIRED FOR AREA.
...MID MS/TN/OH VALLEYS...
TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY FRIDAY
WITHIN NWD-EXPANDING WARM SECTOR WHERE AIR MASS WILL BE WEAKLY
CAPPED AND MODERATELY UNSTABLE. CURRENTLY...IT APPEARS THAT THE
STRONG WIND FIELD ATTENDANT TO UPPER SYSTEM WILL REMAIN W OF THE
WARM SECTOR THROUGH THE DIURNAL HEATING CYCLE. TROPOSPHERIC WINDS
WILL INCREASE CONSIDERABLY FRIDAY NIGHT THROUGH THE MID MS INTO OH
VALLEYS. HOWEVER...BY THIS TIME THERE IS SOME QUESTION WHETHER
ENVIRONMENT WILL SUPPORT SURFACE-BASED STORMS DUE TO INCREASING
CONVECTIVE INHIBITION.
GIVEN THE ABOVE-MENTIONED PHASING ISSUES AND QUESTIONS REGARDING
STABILITY OF WARM SECTOR AIR MASS...WILL ONLY INCLUDE LOW
PROBABILITIES IN THIS FORECAST. AN UPGRADE TO SLIGHT RISK MAY BE
REQUIRED IN LATER OUTLOOKS.
..MEAD.. 09/23/2009
CLICK TO GET WUUS03 PTSDY3 PRODUCT
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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