MESOSCALE DISCUSSION 2021
   NWS STORM PREDICTION CENTER NORMAN OK
   0649 PM CDT MON AUG 16 2004
   
   AREAS AFFECTED...IA
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 755...
   
   VALID 162349Z - 170145Z
   
   CONTINUE WW.
   
   VIGOROUS THUNDERSTORM ACTIVITY IS ONGOING.  MOST INTENSE STORMS HAVE
   BEEN SOUTH OF MASON CITY...WHERE LOW-LEVEL WARM ADVECTION WAS
   MAXIMIZED ALONG THERMAL GRADIENT TO THE EAST SOUTHEAST OF SURFACE
   LOW...NOW NORTH OF SIOUX CITY. HOWEVER...MORE RECENT CONVECTIVE
   DEVELOPMENT HAS TAKEN PLACE UPSTREAM TOWARD SURFACE LOW...SUPPORTED
   BY FORCED ASCENT OF BOUNDARY LAYER WITH MEAN MIXED LAYER CAPE AROUND
   2000 J/KG.  FURTHER INCREASE/INTENSIFICATION OF THUNDERSTORMS
   APPEARS LIKELY IN THIS ENVIRONMENT ACROSS NORTHWEST/CENTRAL IOWA
   DURING THE NEXT COUPLE OF HOURS.  NORTHWESTERLY MID-LEVEL FLOW
   REGIME AND ASSOCIATED SHEAR ARE RATHER WEAK...BUT THERMODYNAMIC
   ENVIRONMENT WILL REMAIN SUPPORTIVE OF LARGE HAIL/DAMAGING WIND GUSTS
   INTO THE EVENING HOURS.
   
   ..KERR.. 08/16/2004
   
   
   ATTN...WFO...DMX...FSD...
   
   42879538 43149436 42869282 42249258 41739233 41399288
   41269381 41579464 42049525 42529588