MESOSCALE DISCUSSION 1963
   NWS STORM PREDICTION CENTER NORMAN OK
   1145 AM CDT SAT AUG 13 2011
   
   AREAS AFFECTED...PARTS OF NRN IL...SERN WI...NRN IND...SWRN LOWER MI
   
   CONCERNING...SEVERE POTENTIAL...WATCH NEEDED SOON 
   
   VALID 131645Z - 131745Z
   
   A WW LIKELY WILL BE ISSUED SOON.
   
   AS THE FRONTAL ZONE ASSOCIATED WITH A DIGGING UPPER TROUGH SLOWLY
   ADVANCES SOUTHEASTWARD THROUGH THE UPPER MIDWEST AND GREAT LAKES
   REGION...SCATTERED CONVECTIVE DEVELOPMENT APPEARS TO BE SLOWLY
   INTENSIFYING ACROSS PARTS OF NORTHERN ILLINOIS INTO SOUTHERN LOWER
   MICHIGAN.  THIS APPEARS TO BE IN RESPONSE TO LARGE-SCALE ASCENT AND
   DESTABILIZATION DOWNSTREAM OF A WEAK FRONTAL WAVE...NOW OVER
   SOUTHWEST WISCONSIN...ASSOCIATED WITH A FAIRLY VIGOROUS SHORT WAVE
   IMPULSE AND EMBEDDED CYCLONIC VORTICITY CENTER DIGGING ACROSS IOWA. 
   AS THE SYNOPTIC FORCING DEVELOPS EAST SOUTHEASTWARD THROUGH
   18-20Z...STORM COVERAGE IS EXPECTED TO INCREASE WEST AND SOUTH OF
   CHICAGO...THROUGH THE CHICAGO METROPOLITAN AREA AND ADJACENT
   NORTHERN INDIANA INTO SOUTHERN LOWER MICHIGAN.
   
   DEEP LAYER WESTERLY MEAN FLOW STILL APPEARS SOMEWHAT MODEST...BUT A
   BAND OF 30-40 KT FLOW IN THE 700 TO 500 MB LAYER MAY ENHANCE
   CONVECTION...AS LOW-LEVEL LAPSE RATES CONTINUE TO STEEPEN WITH
   HEATING OF THE MOIST PRE-FRONTAL BOUNDARY LAYER.  IT PROBABLY IS
   STILL SEVERAL HOURS AWAY FROM A MORE SUBSTANTIVE RISK FOR
   POTENTIALLY DAMAGING SURFACE GUSTS...WHICH MIGHT NOT OCCUR UNTIL
   AFTER 20-21Z SOUTH AND EAST OF CHICAGO THROUGH NORTHERN INDIANA. 
   HOWEVER...RELATIVELY COOL MID-LEVEL TEMPERATURE PROFILES AND
   MODESTLY LARGE CAPE /ON THE ORDER OF 1000-2000 J PER KG/ MAY BE
   CONDUCIVE TO INCREASING LARGE HAIL POTENTIAL IN STRONGER STORMS
   UNTIL THEN.
   
   ..KERR.. 08/13/2011
   
   
   ATTN...WFO...IWX...GRR...IND...LOT...ILX...MKX...DVN...
   
   LAT...LON   42608535 41328476 40448640 40168733 40018873 40578929
               41038988 41878915 42578822 43008686 42608535