SWOMCD
SPC MCD 302046
ILZ000-WIZ000-IAZ000-MNZ000-302145-
MESOSCALE DISCUSSION 0629
NWS STORM PREDICTION CENTER NORMAN OK
0346 PM CDT MON APR 30 2007
AREAS AFFECTED...NERN IA...NW IL...SW WI...SRN MN
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 302046Z - 302145Z
SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS CENTRAL AND NORTHERN
IOWA...NORTHWESTERN ILLINOIS...SOUTHWESTERN WISCONSIN...AND SOUTHERN
MINNESOTA LATE THIS AFTERNOON AND EVENING. STRONG WINDS AND LARGE
HAIL ARE THE PRIMARY EXPECTED THREAT. A SEVERE THUNDERSTORM WATCH
MAY BE NEEDED WITHIN THE NEXT COUPLE OF HOURS.
THE AIRMASS OVER CENTRAL AND NORTHERN IOWA CONTINUES TO DESTABILIZE
THIS AFTERNOON IN RESPONSE TO INCREASED SURFACE HEATING...AND SOME
BUILDING CU HAS BEEN NOTED ON VISIBLE SATELLITE IMAGERY OVER
NORTHEAST IOWA...INDICATING THE BEGINNING OF CONVECTIVE DEVELOPMENT.
STORMS WILL LIKELY FORM IN THIS AREA AND SOUTHEASTWARD...INTO NW
ILLINOIS...ALONG A SLOW-MOVING TO NEAR STATIONARY WARM FRONT THAT
EXTENDS ACROSS THE AREA. STORMS WILL LIKELY BEGIN AS UNORGANIZED
CLUSTERS AND DEVELOP INTO A EAST-NORTHEASTWARD MOVING SQUALL LINE BY
LATER IN THE DAY.
MUCAPE VALUES ARE CURRENTLY AROUND 1500 J/KG AND WILL INCREASE TO
AROUND 2000 J/KG AS SURFACE HEATING CONTINUES...INCREASING THE
CHANCE FOR LARGE HAIL WITH ANY STORMS THAT FORM. FORECAST SOUNDINGS
INDICATE SOME DIRECTIONAL SHEAR ALONG AND JUST AHEAD OF THE WARM
FRONTAL BOUNDARY...SUGGESTING THE POTENTIAL FOR STORM ROTATION...BUT
MOST STORMS ARE EXPECTED TO STAY ELEVATED ABOVE THIS SHALLOW SHEAR
LAYER SO MAINLY MULTICELL STORMS ARE EXPECTED THOUGH SOME STORM
ROTATION MAY BE POSSIBLE WITH A COUPLE OF STORMS.
ADDITIONALLY...GIVEN THE MODERATE TEMPERATURE/DEWPOINT SPREADS NOTED
IN BOTH OBSERVED AND LATEST RUC MODEL FORECAST SOUNDINGS...LOCALIZED
MICROBURSTS WILL BE POSSIBLE WITH THE STRONGEST STORMS.
.LEVIT.. 04/30/2007
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LOT...MKX...DVN...ARX...MPX...DMX...FSD...
42749484 42689423 42599335 42309215 41829117 41439006
41228942 41418910 42148900 42428923 43138972 43549042
43849150 43909309 43879381 43859426 43769477 43509507
43339524 43039530 42839508
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