MESOSCALE DISCUSSION 1978
   NWS STORM PREDICTION CENTER NORMAN OK
   0136 PM CDT FRI SEP 21 2012
   
   AREAS AFFECTED...CNTRL IL...WCNTRL IND
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 211836Z - 212000Z
   
   PROBABILITY OF WATCH ISSUANCE...60 PERCENT
   
   SUMMARY...AN ISOLATED SEVERE THREAT IS EXPECTED TO DEVELOP ACROSS
   CNTRL IL INTO WRN IND THIS AFTERNOON. ISOLATED LARGE HAIL AND WIND
   DAMAGE WILL INITIALLY BE THE MAIN THREAT. AN ISOLATED TORNADO THREAT
   COULD ALSO DEVELOP LATER THIS AFTERNOON. WW ISSUANCE MAY BECOME
   NECESSARY ACROSS THE REGION ONCE THE SCENARIO BEGINS TO UNFOLD.
   
   DISCUSSION...THUNDERSTORMS ARE CURRENTLY INITIATING AND INCREASING
   IN INTENSITY JUST TO THE EAST OF A DEEPENING SFC LOW CENTERED OVER
   NE MO. THE STORMS ARE LOCATED ON THE NERN EDGE OF INSTABILITY AND ON
   THE NOSE OF A MID-LEVEL JET MOVING INTO THE REGION FROM THE WEST
   NORTHWEST. THE STRONG MID-LEVEL FLOW ASSOCIATED WITH THE JET IS
   CREATING FAVORABLE SHEAR PROFILES FOR SEVERE STORMS IN SPITE OF THE
   WEAK INSTABILITY IN PLACE. THE WSR-88D VWP AT SPRINGFIELD IL
   CURRENTLY SHOWS ABOUT 65 KT OF 0-6 KM SHEAR WITH SUBSTANTIAL VEERING
   WITH HEIGHT FROM 2 TO 3 KM. THIS COULD SUPPORT A SUPERCELL THREAT AS
   LOW-LEVEL MOISTURE ADVECTS NWD INTO THE MCD AREA AND INSTABILITY
   INCREASES. 500 MB TEMPS OF -15 C TO -19C WILL BE SUPPORTIVE OF
   ISOLATED LARGE HAIL WITH THE MORE INTENSE CORES. IN
   ADDITION...LOW-LEVEL LAPSE RATES HAVE STEEPENED SOME ACROSS ECNTRL
   IL INTO WRN IND AS SHOWN ON MESOSANALYSIS WITH 0-3 KM LAPSE RATES
   NOW AROUND 7.0 C/KM. THIS ALONG WITH THE STRONG WIND FIELDS AT
   LOW-LEVELS MAY SUPPORT AN ISOLATED WIND DAMAGE AS CELLS MATURE LATE
   THIS AFTERNOON. AN ISOLATED TORNADO THREAT COULD ALSO DEVELOP
   ESPECIALLY IF THE CELLS CAN ROTATE AND PERSIST.
   
   ..BROYLES/MEAD.. 09/21/2012
   
   
   ATTN...WFO...IWX...IND...PAH...LOT...ILX...LSX...DVN...
   
   LAT...LON   40548702 41378876 41728987 41669052 41169094 40539089
               39348998 38558854 38778681 40548702