MESOSCALE DISCUSSION 1829
   NWS STORM PREDICTION CENTER NORMAN OK
   0536 PM CDT SAT AUG 08 2009
   
   AREAS AFFECTED...CNTRL/SRN MN INTO NWRN WI
   
   CONCERNING...TORNADO WATCH 677...678...
   
   VALID 082236Z - 090000Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 677...678...CONTINUES.
   
   UNCERTAINTY EXISTS AS TO WHETHER ADDITIONAL SURFACE-BASED STORM
   DEVELOPMENT WILL OCCUR ACROSS REGION THIS EVENING.  SOME HAIL WILL
   REMAIN POSSIBLE WITH ELEVATED STORMS OVER PORTIONS OF WI.
   
   LATEST MESOANALYSIS INDICATED SURFACE LOW S RWF WITH ASSOCIATED WARM
   FRONT LIFTING NWD...EXTENDING FROM CYCLONE NEWD TO N OF MSP AND THEN
   MORE EWD TO S OF RHI AS OF 22Z.  AIR MASS ALONG AND S OF WARM FRONT
   REMAINS WARM AND QUITE MOIST WITH MLCAPE OF 2000-3000 J/KG. 
   HOWEVER...MODIFICATION OF 18Z MSP SOUNDING FOR CURRENT SURFACE
   CONDITIONS AND PROXIMITY AMDAR DATA INDICATE THAT A CAP STILL EXISTS
   ACROSS THE WARM SECTOR.  MOREOVER...WATER VAPOR IMAGERY SUGGESTS
   THAT SHORT WAVE TROUGH /WHICH MOVED THROUGH PARTS OF NEB AND SD
   EARLIER TODAY/ IS BEGINNING TO LOSE AMPLITUDE AS IT APPROACHES
   MIDLEVEL RIDGE AXIS CENTERED OVER THE UPPER GREAT LAKES.  
   
   THUS...IT APPEARS THAT WEAKENING FORCING FOR ASCENT AND THE
   MAINTENANCE OF A CAP HAVE LIKELY CONTRIBUTED TO THE DEMISE OF
   LONG-LIVED SUPERCELL WHICH MOVED INTO SWRN MN EARLIER TODAY.
   A BAND OF ELEVATED TSTMS HAS RECENTLY DEVELOPED FROM NE OF MSP TO
   NEAR CWA...APPARENTLY DRIVEN BY MOISTENING/ASCENT ABOVE CAP.  ASIDE
   FROM THIS ACTIVITY...THERE IS SOME QUESTION AS TO WHETHER ADDITIONAL
   SURFACE-BASED STORM DEVELOPMENT WILL OCCUR THIS EVENING. THE MOST
   PROBABLE AREA APPEARS TO BE SRN MN WITHIN LOW-LEVEL THERMAL AXIS
   WHERE STRONG DIABATIC HEATING MAY BE SUFFICIENT TO LOCALLY BREACH
   CAP.  EVEN IF STORMS DEVELOP...AREA VWPS AND PROFILER DATA INDICATE
   THAT THE STRONGER LOW-LEVEL SHEAR HAS BECOME DISPLACED WELL TO THE N
   INVOF WARM FRONT.  THUS...THE PRIMARY SEVERE THREATS WOULD BE HAIL
   AND STRONG WIND GUSTS WITH ANY STORMS THAT CAN BECOME ESTABLISHED.
   
   ..MEAD.. 08/08/2009
   
   
   ATTN...WFO...DLH...ARX...MPX...
   
   LAT...LON   43879454 44509511 45119531 45769470 46039296 45929112
               45069062 44159134 43669252 43879454