MESOSCALE DISCUSSION 1683
   NWS STORM PREDICTION CENTER NORMAN OK
   0701 PM CDT SUN JUL 26 2009
   
   AREAS AFFECTED...SE ND...EXTREME NW MN
   
   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 
   
   VALID 270001Z - 270130Z
   
   ISOLATED LARGE HAIL AND A BRIEF TORNADO MAY OCCUR THIS EVENING
   ACROSS SE ND OR ADJACENT AREAS OF EXTREME NW MN...BUT THE THREAT
   SHOULD REMAIN ISOLATED.
   
   SURFACE-BASED CONVECTION IS BEGINNING TO DEVELOP NEAR JMS ALONG A
   SURFACE TROUGH/WEAK COLD FRONT ACROSS SE ND.  THOUGH THIS AREA IS 
   RELATIVELY FAR REMOVED FROM THE ZONE OF LARGER SCALE ASCENT IN
   ADVANCE OF A SHORTWAVE TROUGH DIGGING SEWD OVER SK/MB...SURFACE
   HEATING AND WEAK LOW-LEVEL CONVERGENCE HAVE WEAKENED THE CAP ALONG
   THE SURFACE BOUNDARY.  A CORRIDOR OF LOW 60 DEWPOINTS/MID 80S
   TEMPS...ALONG WITH STEEP LOW-MID LEVEL LAPSE RATES...HAVE RESULTED
   IN MLCAPE AROUND 1500 J/KG.  DEEP LAYER VERTICAL SHEAR IS SUFFICIENT
   FOR SUPERCELLS WITH WEAK SELY LOW-LEVEL FLOW BELOW 40 KT NWLY MID
   LEVEL FLOW.  THE COMBINATION OF INSTABILITY/VERTICAL COULD SUPPORT
   ISOLATED LARGE HAIL FOR A COUPLE OF HOURS THIS EVENING...AND
   POTENTIALLY AN ISOLATED TORNADO GIVEN THE SUPERCELL PROFILES ALONG
   WITH SOMEWHAT ENHANCED VERTICAL VORTICITY ALONG THE BOUNDARY IN THE
   PRESENCE OF STEEP LOW-LEVEL LAPSE RATES.  HOWEVER...STORM COVERAGE
   AND THE SEVERE STORM THREAT ARE EXPECTED TO REMAIN RATHER ISOLATED
   AND SHORT-LIVED THIS EVENING...THUS NO WW IS ANTICIPATED.
   
   ..THOMPSON.. 07/27/2009
   
   
   ATTN...WFO...FGF...BIS...
   
   LAT...LON   47539670 47229643 46969656 46659701 46439784 46339851
               46469887 47079850 47619802 47679704 47539670