MESOSCALE DISCUSSION 0794
   NWS STORM PREDICTION CENTER NORMAN OK
   0940 AM CDT FRI MAY 21 2004
   
   AREAS AFFECTED...NE IL/LWR MI/NRN IND/NW OH
   
   CONCERNING...SEVERE THUNDERSTORM POTENTIAL 
   
   VALID 211440Z - 211645Z
   
   CURRENT INDICATIONS ARE WW MAY NOT BE NEEDED...BUT CONVECTIVE TRENDS
   WILL CONTINUE TO BE CLOSELY MONITORED.
   
   LARGE CLUSTER OF INTENSE CONVECTION NOW PROGRESSING ACROSS THE
   MILWAUKEE/CHICAGO METRO AREAS HAS BEEN SUPPORTED BY AGEOSTROPHIC
   FORCING IN ENTRANCE REGION OF ANTICYCLONIC UPPER JET STREAK ACROSS
   ONTARIO/QUEBEC.  HOWEVER...MODELS SUGGEST THIS FORCING WILL WEAKEN/
   DEVELOP NORTHEASTWARD ACROSS NORTHERN LOWER MICHIGAN THROUGH EARLY
   AFTERNOON...AS UPPER JET SHIFTS NORTHEASTWARD AND UPPER RIDGE SHIFTS
   INTO THE GREAT LAKES REGION AHEAD OF NORTHERN/CENTRAL PLAINS SHORT
   WAVE TROUGH.  IN RESPONSE TO UPSTREAM TROUGH...STRONG SOUTHERLY
   LOW-LEVEL JET AND ASSOCIATED FORCING FOR UPWARD VERTICAL MOTION IS
   PROGGED TO REMAIN FOCUSED ALONG WARM FRONT LIFTING ACROSS MINNESOTA/
   WISCONSIN.  THUS...LARGE-SCALE FORCING FOR CONTINUATION OF STRONG/
   SEVERE MESOSCALE CONVECTIVE SYSTEM EAST OF LOWER LAKE MICHIGAN IS
   UNCERTAIN.
   
   COLD POOL ASSOCIATED WITH ONGOING CONVECTIVE SYSTEM LIKELY WILL
   CONTINUE EAST OF LOWER LAKE MICHIGAN...ALONG WEAK FRONTAL ZONE WHICH
   REMAINS NEAR THE MICHIGAN/INDIANA BORDER INTO NORTHERN OHIO.  THIS
   WILL ENHANCE CONVERGENCE ALONG FRONT IN ENVIRONMENT WHICH IS
   DESTABILIZING WITH HEATING OF BOUNDARY LAYER WITH DEW POINTS AROUND
   70F.  WITH MEAN MIXED LAYER CAPE ON THE ORDER OF 2000 J/KG
   ...SUPPORTIVE OF SEVERE CONVECTION DESPITE WEAK SHEAR...PRIMARY
   UNCERTAINTY IS WHETHER THIS LIFT WILL BE STRONG ENOUGH TO OVERCOME
   RATHER SUBSTANTIAL...AND STRENGTHENING MID-LEVEL CAPPING.
   
   ..KERR.. 05/21/2004
   
   
   ATTN...WFO...CLE...ILN...DTX...APX...IWX...GRR...LOT...MKX...
   
   41678131 40828237 40638422 41078560 41178661 41058772
   41238826 42258851 43148704 44698602 45718471