AREAS AFFECTED...LOWER MI...SERN WI...NRN IL
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 171830Z - 171930Z
PROBABILITY OF WATCH ISSUANCE...5 PERCENT
SUMMARY...A HAIL THREAT WILL ACCOMPANY THE STRONGER TSTMS FORMING
ALONG A COLD FRONT ACROSS LOWER MI. ADDITIONAL DEVELOPMENT MAY OCCUR
FARTHER SE THIS AFTERNOON INTO PARTS OF SERN WI AND NRN IL. A FEW OF
THESE STORMS WILL BE CAPABLE OF PRODUCING MARGINALLY SVR HAIL...BUT
A WW IS UNLIKELY.
DISCUSSION...18Z SFC ANALYSIS SHOWS A COLD FRONT ACROSS NRN LOWER MI
EXTENDING SWWD ACROSS LM TOWARDS THE IA/IL BORDER...ATTENDANT TO A
WEAK SFC LOW POSITIONED W OF APN. WEAK LOW-LEVEL CONVERGENCE ALONG
THE COLD FRONT...COMBINED WITH MODEST MIDLEVEL HEIGHT FALLS...HAVE
SUSTAINED TSTMS OVER NRN LOWER MI...OCCASIONALLY DISPLAYING THE
POTENTIAL TO PRODUCE HAIL. ADDITIONAL CONVECTIVE SHOWERS/TSTMS HAVE
BEGUN TO DEVELOP MORE RECENTLY FARTHER S ACROSS ERN IA/SRN WI. THE
COLD FRONT AND ASSOCIATED TSTMS WILL CONTINUE TO PROGRESS
EWD...WHERE STRONGER HEATING HAS OCCURRED WITH TEMPERATURES REACHING
THE 70S F. STEEP MIDLEVEL LAPSE RATES AND MODEST BOUNDARY LAYER
MOISTURE HAVE YIELDED ESTIMATED MLCAPE VALUES OF 500-1000 J/KG.
STRENGTHENING MIDLEVEL FLOW...AND RESULTANT EFFECTIVE SHEAR NEAR 40
KTS...WILL BE SUPPORTIVE OF A THREAT FOR MARGINALLY SVR HAIL
ACCOMPANYING THE STRONGEST CONVECTIVE CORES...DESPITE THE PRESENCE
OF WEAK INSTABILITY. HOWEVER...THE MAGNITUDE/AREAL COVERAGE OF THE
HAIL THREAT IS EXPECTED TO BE TOO LOW TO WARRANT WW CONSIDERATION.
..ROGERS/MEAD.. 09/17/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...APX...GRR...LOT...MKX...DVN...
LAT...LON 45348424 45478393 45458357 44998322 44528338 44048445
43218562 42528673 41978796 41488909 41518988 41969006
42318990 43158827 43618705 44498550 45348424
