MESO: Mesoscale Discussion 0820

ACUS11 KWNS 161843
SWOMCD
SPC MCD 161842
ILZ000-WIZ000-IAZ000-162015-

MESOSCALE DISCUSSION 0820
NWS STORM PREDICTION CENTER NORMAN OK
0142 PM CDT WED MAY 16 2007

AREAS AFFECTED...CNTRL/SRN WI...NRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 161842Z - 162015Z

THE SEVERE THREAT WILL INCREASE ACROSS CNTRL/SRN WI INTO NRN IL THIS
AFTERNOON AS TSTMS BECOME MORE NUMEROUS INVOF COMPACT MID-LEVEL LOW
SINKING S/SEWD FROM NRN WI. DESPITE PALTRY TOTAL INSTABILITY...VERY
STEEP LOW-LEVEL LAPSE RATES AND MODERATELY STRONG EFFECTIVE SHEAR
SHOULD ALLOW A FEW LOW-TOPPED SUPERCELLS TO DEVELOP. AREA WILL BE
MONITORED FOR A POSSIBLE WW BY 21Z.

18Z SUBJECTIVE SURFACE ANALYSIS DEPICTED A WEAK SURFACE LOW AROUND
20 NE LSE WITH AN ATTENDANT COLD FRONT RUNNING SSW TO AROUND 20 E
ALO AND THEN ARCING MORE WWD NEAR DSM. INVOF OF THESE FEATURES...SCT
SHOWERS AND ISO TSTMS HAVE RECENTLY BEEN SPAWNED ACROSS
W-CNTRL/CNTRL WI SWD ALONG THE MS RIVER INTO FAR NERN IA. MODIFIED
ACARS SOUNDINGS FROM NEAR EAU AND RUC SOUNDINGS ACROSS CNTRL/SRN WI
INDICATE THE PRESENCE OF WEAK INSTABILITY /MLCAPES AOB 250 J/KG/
BENEATH A STRONG MID-LEVEL INVERSION. ADDITIONAL HEATING ACROSS SRN
WI/NRN IL WILL RESULT IN FURTHER DESTABILIZATION...LIKELY TO AROUND
500 J/KG. ALTHOUGH SURFACE FLOW WILL REMAIN LIGHT...EFFECTIVE BULK
SHEARS OF 30 TO 35 KTS IN COMBINATION WITH COMPACT VORTICITY
MAXIMUM...SHOULD BE SUFFICIENT FOR UPDRAFT ROTATION AND POTENTIAL
LOW-TOPPED SUPERCELLS. IN ADDITION TO MARGINALLY SEVERE HAIL AND
GUSTY WIND THREATS...VERY STEEP 0-3 KM LAPSE RATES /AROUND 9 DEG
C/KM/ AND 0-3 KM CAPES AROUND 200 J/KG /AS DEPICTED BY RUC FORECAST
SOUNDINGS OVER SERN WI/ SHOULD ENHANCE LOW-LEVEL STRETCHING
POTENTIAL. IF THIS OCCURS...BRIEF TORNADOES MAY DEVELOP WITHIN THIS
REGIME.

.GRAMS.. 05/16/2007

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

ATTN...WFO...GRB...LOT...MKX...DVN...ARX...

44558947 43768869 43018821 42178790 41828791 41518832
41458895 41668978 42079018 42829035 43689070 44509098
44769044

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