Tornado Watch Likely

[NWIASpotter]

The SPC has put out a new mesoscale discussion for portions of SD, NE, MN, and IA.

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...