MESO: Mesoscale Discussion 1978

ACUS11 KWNS 211837
SWOMCD
SPC MCD 211836
INZ000-ILZ000-IAZ000-212000-

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

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...IWX...IND...PAH...LOT...ILX...LSX...DVN...

LAT...LON 40548702 41378876 41728987 41669052 41169094 40539089
39348998 38558854 38778681 40548702

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