MESOSCALE DISCUSSION 1268
   NWS STORM PREDICTION CENTER NORMAN OK
   0651 PM CDT SUN JUN 21 2009
   
   AREAS AFFECTED...CNTRL AND NRN IA THROUGH EXTREME SRN MN
   
   CONCERNING...TORNADO WATCH 488...
   
   VALID 212351Z - 220115Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 488 CONTINUES.
   
   THREAT FOR ISOLATED TORNADOES EXPECTED TO PERSIST ANOTHER FEW HOURS
   IN WW 488...WITH GREATER THREAT EXPECTED ACROSS NRN IA INTO EXTREME
   SRN MN. THREAT MAY SHIFT A LITTLE FARTHER NORTH IN SRN MN...AND
   ANOTHER ROW OF COUNTIES MIGHT NEED TO BE ADDED TO NRN PORTIONS OF
   WW.
   
   EARLY THIS EVENING A WARM FRONT EXTENDS FROM A WEAK SURFACE LOW IN
   SERN SD SEWD FROM NWRN THROUGH SERN IA INTO SRN IL. A COLD FRONT
   STRETCHED FROM THE SURFACE LOW TO THE SD/IA BORDER...THEN SWWD
   THROUGH ERN NEB. DISCRETE STORMS CONTINUE DEVELOPING...PRIMARILY
   WITHIN ZONE OF ISENTROPIC LIFT ALONG AND NORTH OF THE WARM FRONT AS
   WELL AS FARTHER WEST ALONG AND JUST EAST OF THE COLD FRONT. GREATER
   TORNADO THREAT IS EXPECTED TO REMAIN OVER NRN TWO THIRDS OF WW FROM
   NRN-E CNTRL IA INTO SRN MN WHERE BACKED SELY FLOW IS RESULTING IN
   LARGER LOW LEVEL HODOGRAPHS. TREND HAS BEEN FOR BOUNDARY LAYER TO
   RECOVER NWD WITH TIME FARTHER INTO SRN MN IN WAKE OF LOW CLOUD BAND.
   EFFECTIVE STORM RELATIVE HELICITY AROUND 200-300 M2/S2 AND MODERATE
   INSTABILITY WILL CONTINUE TO SUPPORT A THREAT OF ISOLATED TORNADOES
   WITH SUPERCELLS LIFTING NORTH OF THE WARM FRONT THROUGH NRN IA AND
   SRN MN NEXT FEW HOURS. THERMODYNAMIC ENVIRONMENT IS NOT OPTIMAL AND
   HAIL THREAT WILL LIKELY REMAIN LIMITED BY POOR MID LEVEL LAPSE RATES
   AND WARM MID LEVEL TEMPERATURES.
   
   LESS FAVORABLE LOW LEVEL HODOGRAPHS EXIST SOUTH OF THE FRONT OVER
   THE SWRN PORTION OF THE WW WHERE SURFACE WINDS HAVE VEERED TO SWLY
   AND WHERE UPDRAFTS MAY CONTINUE TO STRUGGLE DUE TO SUBSIDENCE IN
   WAKE OF EJECTING WAVE AND LACK OF A LOW LEVEL FOCUS FOR ASCENT.
   
   ..DIAL.. 06/21/2009
   
   
   ATTN...WFO...DVN...ARX...MPX...DMX...FSD...OAX...
   
   LAT...LON   43919300 42929145 41539152 41679295 41969443 42109541
               42349612 43979581 43919300