MESO: Mesoscale Discussion 0850

ACUS11 KWNS 201817
SWOMCD
SPC MCD 201817
ILZ000-WIZ000-IAZ000-202015-

MESOSCALE DISCUSSION 0850
NWS STORM PREDICTION CENTER NORMAN OK
0117 PM CDT SUN MAY 20 2012

AREAS AFFECTED...SRN WI THROUGH NRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 201817Z - 202015Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...STORMS ARE EXPECTED TO DEVELOP FROM SRN WI INTO PARTS OF
NWRN IL BY 20Z. STRONGER STORMS COULD PRODUCE LOCALLY STRONG TO
DAMAGING WIND GUSTS AND HAIL. WW MIGHT BE NEEDED ONCE THUNDERSTORM
INITIATION APPEARS IMMINENT.

DISCUSSION...THIS AFTERNOON A COLD FRONT EXTENDS FROM WRN WI...ERN
IA INTO NERN MO WITH WEAK PRE-FRONTAL CONVERGENCE BANDS INDICATED
AHEAD OF THE FRONT. WARM SECTOR HAS BECOME MODERATELY UNSTABLE
SUPPORTED BY A PLUME OF STEEPER /7-7.5 C/KM/ LAPSE RATES ABOVE UPPER
50S BOUNDARY LAYER DEWPOINTS. PRE-FRONTAL NEAR SFC WINDS HAVE VEERED
TO SSWLY TO THE SOUTH OF A NEWD EJECTING SHORTWAVE TROUGH LOCATED
OVER THE UPPER MS VALLEY. THIS IS CONTRIBUTING TO WEAKER CONVERGENCE
ALONG COLD FRONT. MOREOVER...DEEPER FORCING ASSOCIATED WITH EJECTING
SHORTWAVE TROUGH WILL REMAIN NORTH OF THIS REGION. THESE FACTORS
MAKE TIMING AND EXTENT OF THUNDERSTORM INITIATION IN THIS AREA
SOMEWHAT UNCERTAIN. HOWEVER...AS TEMPERATURES WARM INTO THE UPPER
80S...CONVECTIVE INHIBITION SHOULD WEAKEN ENOUGH FOR STORMS TO
DEVELOP WHERE DEEPER BAROCLINIC ZONE INTERACTS WITH THE UNSTABLE
WARM SECTOR. STRONGER FLOW ALOFT ATTENDING THE EJECTING IMPULSE WILL
REMAIN NORTH OF THIS REGION WITH DEEP SHEAR GENERALLY AOB 30 KT
SUPPORTIVE OF MULTICELLS. NEVERTHELESS...THE THERMODYNAMIC
ENVIRONMENT WITH MODERATE INSTABILITY...STEEP MID LEVEL LAPSE RATES
AND LARGE BOUNDARY LAYER TEMPERATURE-DEWPOINT SPREADS WILL PROMOTE A
THREAT OF ISOLATED DAMAGING WIND AND HAIL.

..DIAL/WEISS.. 05/20/2012

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

ATTN...WFO...LOT...ILX...MKX...LSX...DVN...

LAT...LON 43608819 42808789 41928772 41158759 40068903 39549085
40469091 42669002 43678933 43608819

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