MESO: Mesoscale Discussion 1979

ACUS11 KWNS 212200
SWOMCD
SPC MCD 212159
INZ000-ILZ000-MOZ000-212330-

MESOSCALE DISCUSSION 1979
NWS STORM PREDICTION CENTER NORMAN OK
0459 PM CDT FRI SEP 21 2012

AREAS AFFECTED...PORTIONS OF SRN/CNTRL IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 212159Z - 212330Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...ISOLATED TO SCATTERED THUNDERSTORM DEVELOPMENT IS FORECAST
TO OCCUR OVER PORTIONS OF SRN/CNTRL IL DURING THE NEXT FEW HRS. A
FEW STORMS MAY APPROACH SVR LEVELS...AND POSE A THREAT FOR DAMAGING
WIND GUSTS AND HAIL NEAR 1 INCH IN DIAMETER.

DISCUSSION...AT 21Z...SURFACE OBSERVATIONS SHOW AN AREA OF LOW
PRESSURE OVER FAR W-CNTRL IL...WITH A WARM FRONT EXTENDING E-SEWD
INTO SRN IND. LOW-LEVEL WAA REGIME HAS SUSTAINED CLUSTERS OF
ELEVATED STORMS N OF THE WARM FRONT OVER CNTRL IL INTO CNTRL IND
DURING THE AFTERNOON. S OF THE WARM FRONT...TEMPERATURES HAVE WARMED
INTO THE MID TO UPPER 70S...WITH DEWPOINTS RANGING FROM THE UPPER
50S TO LOW 60S. A COLD FRONT ALSO EXTENDED S-SWWD FROM THE LOW INTO
SRN MO. CONVERGENCE/ASCENT ALONG THE COLD FRONT COMBINED WITH A
DESTABILIZING BOUNDARY LAYER APPEARS TO BE AIDING IN ISOLATED
THUNDERSTORM DEVELOPMENT NEAR/JUST E OF STL AS OF 2148Z. GIVEN THE
PRESENCE OF MARGINAL BOUNDARY LAYER MOISTURE AND A NARROW AXIS OF
MLCAPE AROUND 500 J/KG...THE THERMODYNAMIC ENVIRONMENT DOES NOT
APPEAR TO SUPPORT WIDESPREAD SVR THUNDERSTORM DEVELOPMENT.
HOWEVER...FAVORABLE LOW- AND DEEP-LAYER VERTICAL WIND SHEAR PROFILES
MAY AID IN THE DEVELOPMENT OF ONE OR TWO SVR STORMS CAPABLE OF
PRODUCING DAMAGING WIND GUSTS AND HAIL NEAR 1 INCH IN DIAMETER.

..GARNER/THOMPSON.. 09/21/2012

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

ATTN...WFO...IND...PAH...ILX...LSX...

LAT...LON 38458771 37778824 37698916 37938996 38639039 39289012
39448935 39368824 39088765 38458771

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