AREAS AFFECTED...FAR ERN IA...NRN AND W-CNTRL IL...SRN WI
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 032129Z - 032300Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...SCATTERED THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS FAR
ERN IA...NRN AND W-CNTRL IL...AND SRN WI THIS EVENING. A FEW STORMS
MAY BECOME STRONG TO SEVERE...POSING AN ISOLATED THREAT FOR DAMAGING
WIND GUSTS AND PERHAPS A BRIEF TORNADO.
DISCUSSION...WV IMAGERY AT 21Z SHOWS A VORT LOBE PROGRESSING EWD
INTO THE UPPER MS VALLEY REGION...WHILE AN ASSOCIATED SURFACE COLD
FRONT EXTENDED SWWD FROM NRN WI INTO CNTRL/ERN IA AND NRN MO. A WARM
FRONT WAS ALSO RETREATING NWD INTO CNTRL WI AND LOWER MI. DEWPOINTS
AHEAD OF THE COLD FRONT RESIDE IN THE UPPER 50S...WHILE TEMPERATURES
HAVE WARMED INTO THE 60S TO AROUND 70F. HOWEVER... STRONGER BOUNDARY
LAYER DESTABILIZATION HAS BEEN INHIBITED BY PRE-FRONTAL
STRATOCUMULUS. GIVEN ONLY MODEST SURFACE HEATING AND
MOISTURE...COMBINED WITH RATHER WEAK MIDLEVEL LAPSE RATES...SBCAPE
VALUES ONLY RANGE FROM 500-1000 J/KG.
AS THE COLD FRONT PROGRESSES EWD ACROSS THE AREA THIS
EVENING...SCATTERED THUNDERSTORMS ARE FORECAST TO DEVELOP. A MESSY
CONVECTIVE MODE...CONSISTING MAINLY OF LINE SEGMENTS...MAY UNFOLD
DUE TO WEAK BOUNDARY LAYER DESTABILIZATION AND MODEST 30-40 KT
DEEP-LAYER SHEAR. IN ADDITION...STRONGER DCVA/LARGE-SCALE FORCING
FOR ASCENT IS FORECAST TO BE N OF THE AREA...WHICH COULD OTHERWISE
COMPENSATE SOMEWHAT FOR THE LOW CAPE/MODERATE SHEAR ENVIRONMENT.
THEREFORE...EXPECT ISOLATED STRONG/SEVERE WIND GUSTS TO BE THE
PRIMARY THREAT WITH STORMS TONIGHT. IN ADDITION...A 40-50 KT S-SWLY
LLJ WILL AID IN EFFECTIVE SRH VALUES NEAR 200 M2 S-2. THUS...A BRIEF
TORNADO CANNOT BE RULED OUT.
..GARNER/MEAD.. 12/03/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...GRB...LOT...ILX...MKX...LSX...DVN...ARX...
LAT...LON 41468788 40068942 39609050 39809135 40799162 42609078
43838958 44198813 41468788
