MESOSCALE DISCUSSION 1691
   NWS STORM PREDICTION CENTER NORMAN OK
   0332 PM CDT FRI JUL 22 2011
   
   AREAS AFFECTED...WRN AND CNTRL OH...EXTREME SE MI...EXTREME E-CNTRL
   IND
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 670...
   
   VALID 222032Z - 222200Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 670
   CONTINUES.
   
   AS OF 20Z...STRONG TO SEVERE TSTMS CONTINUED ACROSS MUCH OF WW
   670...WITH MORE LINEAR CONVECTION ASSOCIATED WITH A LONG-LIVED MCS
   ACROSS NWRN OH TRAILING INTO E-CNTRL IND...WHILE OTHER STORMS HAVE
   DEVELOPED ALONG AND NORTH OF A WEAK COOL FRONT/LAKE BREEZE BOUNDARY
   ACROSS NERN OH. 
   
   STRONG INSTABILITY IS IN PLACE SOUTH OF THE BOUNDARY...WITH MLCAPES
   OF 3000-4000 J/KG ACCORDING TO MOST RECENT SFC OBJECTIVE ANALYSIS.
   SHEAR IS STRONGEST IN THE IMMEDIATE VICINITY OF THE BOUNDARY ACROSS
   NRN OH...WITH EFFECTIVE SHEAR OF AROUND 30 KTS. FURTHER SOUTH ACROSS
   CNTRL AND SRN OH...SHEAR IS MUCH WEAKER....WITH EFFECTIVE SHEAR
   GENERALLY AOB 20 KTS. CONVECTIVE COVERAGE HAS BEEN LIMITED IN THE
   SERN PARTS OF THE WATCH THUS FAR...LIKELY DUE TO WEAKER CONVERGENCE
   AND CLOSER PROXIMITY TO UPPER RIDGE. 
   
   GREATEST THREAT OF ORGANIZED SEVERE WILL REMAIN ACROSS NRN HALF OF
   OH WHERE THERE IS GREATER OVERLAP BETWEEN STRONG INSTABILITY AND
   MORE FAVORABLE SHEAR VALUES. LONG-LIVED MCS ACROSS NWRN OH WILL
   LIKELY TEND TO WEAKEN WITH TIME AS IT MOVES INTO AREAS ALREADY
   STABILIZED BY ONGOING CONVECTION. SOME BACKBUILDING WILL BE POSSIBLE
   ALONG SWRN EDGE OF WEAKENING MCS ACROSS E-CNTRL IND INTO WRN AND SRN
   OH...WITH ISOLATED SEVERE WINDS POSSIBLE.
   
   ..DEAN.. 07/22/2011
   
   
   ATTN...WFO...PBZ...RLX...CLE...ILN...DTX...IWX...IND...
   
   LAT...LON   40168532 40688472 41448384 41898350 42048294 41978250
               41768204 41438173 41028156 40758158 40468164 40348165
               39648201 39288242 39078302 39118336 39358386 39618490
               40028522 40168532