SWODY1
SPC AC 231556
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1056 AM CDT TUE SEP 23 2008
VALID 231630Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF MN...WESTERN
WI...AND WESTERN IA...
...MN/WI/IA/KS...
MORNING WATER VAPOR IMAGERY SHOWS A LARGE UPPER TROUGH OVER THE
NORTHERN PLAINS...WITH A POTENT SHORTWAVE TROUGH LIFTING
NORTHEASTWARD INTO WESTERN MN. THIS FEATURE IS PROMOTING SCATTERED
SHOWERS AND THUNDERSTORMS OVER EASTERN MN/WESTERN WI. THIS LEAD
IMPULSE IS FORECAST TO LIFT NORTHEASTWARD AND AWAY FROM THE MIDWEST
STATES TODAY...WHILE A SECONDARY AND WEAKER TROUGH APPROACHES FROM
SD/NEB. POCKETS OF STRONG HEATING AHEAD OF THIS TROUGH WILL HELP TO
DESTABILIZE AIRMASS WITH AFTERNOON MLCAPE VALUES OF 500-1500 J/KG
EXPECTED. MODEL GUIDANCE SHOWS CONCENSUS THAT BAND OF CONVECTION
WILL INTENSIFY LATER THIS AFTERNOON AND EARLY EVENING AHEAD OF THIS
TROUGH FROM PARTS OF KS NORTHWARD INTO IA/MN. VERTICAL SHEAR AND
LARGE SCALE FORCING WILL BE RATHER WEAK FROM CENTRAL IA
SOUTHWARD...SUGGESTING THAT SEVERE THREAT WILL BE QUITE LOCALIZED.
HOWEVER...FORECAST SOUNDINGS OVER MN AND NORTHERN IA INDICATE
SUFFICIENT EFFECTIVE SHEAR FOR ORGANIZED MULTICELL TO SUPERCELL
STORM STRUCTURES. HAIL WILL BE POSSIBLE IN STRONGER STORMS...ALONG
WITH AN INCREASING RISK OF LOCALLY DAMAGING WINDS THROUGH THE
EVENING. SEVERE THREAT IS EXPECTED TO DIMINISH TOWARD MIDNIGHT AS
DIURNAL COOLING OCCURS.
...DAKOTAS...
STRONG LARGE SCALE FORCING AHEAD OF MAIN UPPER LOW WILL TRACK
EASTWARD ACROSS ND AND NORTHERN SD TODAY. STRONG DAYTIME HEATING
ACROSS THIS AREA WILL LIKELY YIELD STEEP LOW/MID LEVEL LAPSE RATES
AND THE POTENTIAL FOR AT LEAST A MARGINALLY UNSTABLE AIRMASS.
SCATTERED THUNDERSTORMS ARE EXPECTED BY MID AFTERNOON. FORECAST
SOUNDINGS SUGGEST A RISK OF SMALL HAIL IN STORMS AS THEY MATURE.
PRESENT INDICATIONS ARE THAT WESTERLY LOW LEVEL FLOW WILL HELP TO
TRANSPORT DRIER AIR FROM MT...LIMITING THE POTENTIAL FOR STRONGER
INSTABILITY AND AN ORGANIZED SEVERE THREAT.
..HART/HURLBUT.. 09/23/2008
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