MESOSCALE DISCUSSION 1817
   NWS STORM PREDICTION CENTER NORMAN OK
   0148 PM CDT SUN AUG 01 2004
   
   AREAS AFFECTED...ERN SD/SWRN MN/NERN NEB/NWRN IA
   
   CONCERNING...SEVERE THUNDERSTORM POTENTIAL 
   
   VALID 011848Z - 012045Z
   
   TORNADO WATCH LIKELY WILL BE ISSUED FOR PORTIONS OF ERN SD...SWRN MN
   ...NERN NEB AND NWRN IA WITHIN THE NEXT 1 TO 2 HOURS.
   
   OUTFLOW BOUNDARY FROM EARLIER CONVECTION EXTENDS FROM DSM TO SOUTH
   OF SUX...AND THEN NWWD INTO CENTRAL SD TO A LOW PRESSURE SYSTEM NEAR
   PIR. A WEAK COLD FRONT ALSO WAS PUSHING SLOWLY SWD AND EXTENDED FROM
   THE SURFACE LOW IN CENTRAL SD NEWD INTO NRN MN. THE AIR MASS BETWEEN
   THESE TWO BOUNDARIES HAS BECOME STRONGLY UNSTABLE WITH MLCAPES
   APPROACHING 3000 J/KG...AND WILL CONTINUE DESTABILIZING WITH
   ADDITIONAL HEATING.
   
   SATELLITE IMAGERY SUGGESTS A SHORTWAVE TROUGH IS MOVING EWD INTO THE
   CENTRAL DAKOTAS. THE ABR 18Z SOUNDING SHOWS THE CAP HAS WEAKENED
   CONSIDERABLY SINCE THE 12 RUN. THE CAPPING INVERSION SHOULD CONTINUE
   ERODING DURING THE NEXT COUPLE OF HOURS AS THE UPPER TROUGH NEARS
   THE AREA. GIVEN THE STRONG INSTABILITY AND DEEP LAYER SHEAR AT 45
   KT...ONCE STORMS DEVELOP...THEY SHOULD EVOLVE QUICKLY INTO
   SUPERCELLS. HAIL 3 INCHES OR LARGER WILL BE THE MAIN THREAT...BUT
   THE BACKED BOUNDARY LAYER WINDS NORTH OF THE OUTFLOW BOUNDARY SHOULD
   PROVIDE SUFFICIENT LOW LEVEL SHEAR FOR A FEW TORNADOES.
   
   ..IMY.. 08/01/2004
   
   
   ATTN...WFO...MPX...DMX...FGF...FSD...OAX...ABR...
   
   43829844 45739847 45789742 45719448 44829424 43349404
   41659424 42349817