MESOSCALE DISCUSSION 1270
   NWS STORM PREDICTION CENTER NORMAN OK
   0906 PM CDT SUN JUN 21 2009
   
   AREAS AFFECTED...S CNTRL MN THROUGH NRN AND ERN IA
   
   CONCERNING...TORNADO WATCH 488...
   
   VALID 220206Z - 220300Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 488 CONTINUES.
   
   STORMS WILL CONTINUE INTO THE EVENING FROM S CNTRL MN THROUGH ERN
   IA...AND MAY LATER SPREAD INTO NWRN IL. PRIMARY TORNADO THREAT IS
   EXPECTED TO PERSIST FOR ANOTHER COUPLE HOURS. STORM MODE MAY
   EVENTUALLY TRANSITION TO MCS CLUSTERS WITH THREAT TRANSITIONING TO
   HEAVY RAIN AND POSSIBLY ISOLATED DAMAGING WIND. TORNADO WATCH 488 IS
   SCHEDULED TO EXPIRE AT 03Z. DEPENDING ON SHORT TERM MODE/INTENSITY
   TRENDS CURRENT TORNADO WATCH MIGHT NEED TO BE REPLACED BY ANOTHER WW
   DURING THE NEXT HOUR. ANOTHER POSSIBILITY WILL BE FOR A PORTION OF
   THE WATCH TO BE LOCALLY EXTENDED.
   
   THIS EVENING A BAND OF STORMS...STILL CONTAINING EMBEDDED SUPERCELL
   STRUCTURES...CONTINUES DEVELOPING FROM S CNTRL MN SEWD THROUGH
   E-CNTRL IA WITHIN ZONE OF ISENTROPIC LIFT NORTH OF QUASI-STATIONARY
   FRONT THAT EXTENDS FROM SWRN MN SEWD THROUGH SERN IA. TENDENCY MAY
   BE FOR STORMS TO EVENTUALLY CONGEAL INTO CLUSTERS...WITH THREAT
   GRADUALLY TRANSITIONING TO ISOLATED DAMAGING WIND AND HEAVY RAIN.
   WITH LOW LEVEL JET NOT FORECAST TO UNDERGO A SIGNIFICANT INCREASE
   TONIGHT ALONG WITH A STABILIZING BOUNDARY LAYER...THINKING IS THAT
   TORNADO THREAT SHOULD DECREASE AFTER ABOUT 04-05Z...ESPECIALLY IF
   STORM MODE BEGINS TO TRANSITION TO CLUSTERS. ANY HAIL THREAT WILL
   REMAIN LIMITED BY WARM AIR ALOFT AND POOR LAPSE RATES.
   
   ..DIAL.. 06/22/2009
   
   
   ATTN...WFO...DVN...ARX...MPX...DMX...
   
   LAT...LON   41939101 41339107 41399204 42749327 43309392 44009438
               44109329 42829168 41939101