AREAS AFFECTED...NRN IL INTO NWRN IND AND SWRN LOWER MI
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 251252Z - 251345Z
PROBABILITY OF WATCH ISSUANCE...60 PERCENT
SUMMARY...A SVR TSTM WATCH MAY BE NEEDED FOR PART OF NRN IL INTO
NWRN IND /INCLUDING THE CHICAGO METRO AREA/...AND POSSIBLY SWRN
LOWER MI. A LINE OF TSTMS WILL MOVE E/ESEWD THIS MORNING...POSING A
THREAT FOR DAMAGING WINDS --- ESPECIALLY WITH EWD EXTENT AS THE
BOUNDARY LAYER DESTABILIZES.
DISCUSSION...A CLUSTER OF TSTMS THAT WAS LOCATED IN CENTRAL TO NERN
IA HAVE GROWN UPSCALE INTO A FORWARD PROPAGATING MCS ACROSS THE
UPPER MS VALLEY EARLY THIS MORNING. AT 1220Z...MOSAIC RADAR IMAGERY
SHOWED A LINE OF STORMS WITH THIS MCS EXTENDING FROM EXTREME SOUTH
CENTRAL WI /GREEN COUNTY/ TO ALONG THE NWRN IL/IA BORDER /CARROLL
COUNTY IL TO CLINTON COUNTY IA/. ADDITIONAL STORMS WERE DEVELOPING
FARTHER TO THE SOUTH...JUST TO THE EAST OF KMLI. THIS LINE OF
STORMS WAS MOVING ESEWD CLOSE TO 45 KT...AND THUS FAR HAS REMAINED
LOCATED NORTH OF AN E-W ORIENTED OUTFLOW BOUNDARY FROM AN EARLIER
CONVECTIVE SYSTEM. DESPITE THE CURRENT LOCATION OF THE CONVECTIVE
LINE...WHICH HAS SHOWN SOME TENDENCY TO BOW...VISIBLE SATELLITE
IMAGERY INDICATED POTENTIAL FOR SURFACE HEATING OVER NRN IL AND
TEMPERATURES ARE ALREADY RISING PER TRENDS IN SURFACE OBSERVATIONS.
ADDITIONAL SURFACE HEATING WILL AID IN THE DEVELOPMENT FOR STRONGER
INSTABILITY AND THE POTENTIAL FOR STRONGER WIND GUSTS TO REACH THE
SURFACE...GIVEN DEWPOINTS ALONG AND SOUTH OF THE E-W BOUNDARY OF
AROUND 70 DEGREES. THIS BOUNDARY EXTENDED FROM FAR NWRN OH WWD
THROUGH NRN IND /15 N KFWA TO 30 SW KVPZ/ INTO NRN IL /15 ENE KMMO
TO 25 NE KMLI/.
THE DESTABILIZATION COMBINED WITH A 40-50 KT WLY MIDLEVEL JET
EXTENDING FROM ERN IA TO SRN LOWER MI SUGGESTS STORMS COULD PERSIST
EWD...AT LEAST TO SRN LAKE MICHIGAN AND POSSIBLY INTO FAR NWRN IND
AND SWRN LOWER MI. HOWEVER...A WEAKENING TREND OF A WLY LLJ COULD
PROVE A LIMITING FACTOR IN THE EWD SPEED OF THIS LINE OF STORMS.
THUS...WW ISSUANCE IS POSSIBLE THIS MORNING IF A BOWING STRUCTURE
BECOMES BETTER ORGANIZED.
..PETERS/HART.. 06/25/2013
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...IWX...GRR...LOT...DVN...
LAT...LON 41779014 42108982 42478964 42438796 42378723 42198542
41578551 41108591 41298766 41508897 41779014
