MESOSCALE DISCUSSION 0396
   NWS STORM PREDICTION CENTER NORMAN OK
   0130 PM CDT SUN APR 10 2011
   
   AREAS AFFECTED...EXTREME SERN MN...NERN IA...NWRN IL AND MUCH OF WI
   
   CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 
   
   VALID 101830Z - 102030Z
   
   OUTBREAK OF SEVERE STORMS IS EXPECTED THIS AFTERNOON...INITIALLY
   FROM ERN MN THROUGH NERN IA...THEN SPREADING RAPIDLY EWD THROUGH WI
   AND EXTREME NWRN IL. SUPERCELLS WITH STRONG TORNADOES...VERY LARGE
   HAIL AND DAMAGING WIND WILL BE THE MAIN THREATS. A TORNADO WATCH
   WILL LIKELY BE ISSUED BY 20Z.
   
   THIS AFTERNOON A COLD FRONT EXTENDS FROM A DEEP LOW PRESSURE AREA IN
   E-CNTRL MN SSWWD THROUGH SRN MN...NWRN IA INTO SERN NEB WITH A WARM
   FRONT FROM THE SURFACE LOW IN E-CNTRL MN THROUGH NRN WI. THE LOW
   WILL DEVELOP EWD TO NEAR THE WI BORDER BY 21Z. NEWD ADVECTION OF
   HIGHER THETA-E AIR ALONG A STRONG SSWLY LLJ BENEATH EML PLUME /8.5
   C/KM LAPSE RATES/ AND DIABATIC WARMING IS RESULTING IN NEWD
   DESTABILIZATION WITH TIME. HOWEVER...THE BOUNDARY LAYER REMAINS
   CAPPED BY THE WARM EML AS EVIDENCED BY 18Z MINNEAPOLIS SOUNDING.
   
   UPPER JET IS SHIFTING NEWD INTO THE UPPER MS VALLEY. RAPID ACCAS
   DEVELOPMENT RECENTLY OBSERVED FROM NERN IA THROUGH SWRN WI IS LIKELY
   INDICATIVE OF NEWD EXPANDING ZONE OF AGEOSTROPHIC FORCING WITHIN THE
   UPPER JET EXIT REGION. THIS FORCING IN CONJUNCTION WITH FRONTAL
   CONVERGENCE WILL LIKELY MAINTAIN A DEEPER ZONE OF ASCENT THAT SHOULD
   EVENTUALLY ERODE THE CAP ENOUGH FOR STORMS TO DEVELOP ALONG THE COLD
   FRONT FROM ERN MN INTO NERN IA. STORMS WILL LIKELY MAINTAIN DISCRETE
   MODES FOR SEVERAL HOURS AND WILL BE EMBEDDED WITHIN STRONG DEEP
   LAYER WIND AND VERTICAL SHEAR SUPPORTIVE OF SUPERCELLS. LARGEST
   HODOGRAPHS ARE EXPECTED ACROSS CNTRL THROUGH NRN WI WHERE NEAR
   SURFACE WINDS SHOULD REMAIN BACKED TO SLY EAST OF THE SURFACE LOW
   WITH 0-1 KM STORM RELATIVE HELICITY EXCEEDING 250 M2/S2. STORMS
   DEVELOPING WITHIN THIS ENVIRONMENT WILL LIKELY BECOME CAPABLE OF
   PRODUCING STRONG TORNADOES...VERY LARGE HAIL AND DAMAGING WIND.
   
   ..DIAL.. 04/10/2011
   
   
   ATTN...WFO...GRB...LOT...MKX...DVN...DLH...ARX...MPX...DMX...
   
   LAT...LON   46229080 45298846 44028810 42788874 41958994 42059190
               43759253 45569298 46229080