WEATHER HAZARDS EXPECTED:

THUNDERSTORMS...SOME MAY BE SEVERE WITH THE POTENTIAL TO
PRODUCE: CLOUD TO GROUND LIGHTNING. LARGE HAIL OF 1 TO 2 INCHES.
STRONG DAMAGING WIND GUSTS IN EXCESS OF 60 MPH. LOCALLY HEAVY
RAINFALL. ISOLATED TORNADOES.

AREAS AFFECTED AND TIMING:

THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A COLD FRONT ACROSS
SOUTHEAST IOWA VERY LATE THIS AFTERNOON OR EARLY THIS EVENING...
AND THEN SPREAD EAST INTO ILLINOIS DURING THE EVENING HOURS AND
INTO NORTHWEST INDIANA DURING THE LATE EVENING AND EARLY
OVERNIGHT HOURS. THUNDERSTORMS WOULD LIKELY AFFECT NORTH CENTRAL
ILLINOIS AFTER 7 OR 8 PM...REACHING NORTHEAST ILLINOIS AFTER 9
OR 10 PM AND NORTHWEST INDIANA TOWARD MIDNIGHT.

DISCUSSION:

DEEP LOW PRESSURE OVER NORTHERN IOWA WILL TRACK NEAR THE
ILLINOIS WISCONSIN BORDER TO SOUTHERN LAKE MICHIGAN THIS
EVENING...AND TO CENTRAL LOWER MICHIGAN BY MONDAY MORNING. VERY
WARM AND MOIST AIR WILL CONTINUE TO SPREAD NORTH ACROSS THE
OUTLOOK AREA AHEAD OF THE LOW THIS EVENING. THUNDERSTORMS ARE
EXPECTED TO DEVELOP ACROSS SOUTHEAST IOWA AND NORTHERN MISSOURI
ALONG A COLD FRONT TRAILING FROM THE LOW TOWARD EVENING...AND
WILL MOVE INTO NORTHERN ILLINOIS DURING THE EVENING HOURS AND
INTO INDIANA OVERNIGHT. THE COMBINATION OF WARM AND MOIST LOW
LEVEL AIR...AND STRONG WINDS BOTH AT THE SURFACE AND ALOFT WILL
SUPPORT THE DEVELOPMENT OF SEVERE STORMS...THOUGH WARM AIR ALOFT
WILL LIKELY LIMIT THE DEVELOPMENT OF THUNDERSTORMS EXCEPT NEAR
THE COLD FRONT. THEREFORE THE GREATEST POTENTIAL FOR SEVERE
WEATHER IS EXPECTED TO BE OVER WESTERN PORTIONS OF ILLINOIS AND
THE WESTERN PORTIONS OF THE OUTLOOK AREA. STORMS MAY INITIALLY
BE MORE DISCRETE AND MAY POSE A THREAT OF VERY LARGE
HAIL...DAMAGING WINDS AND EVEN ISOLATED TORNADOES DURING THE
EARLY TO MID EVENING HOURS. STORMS SHOULD EVENTUALLY MERGE INTO
A SQUALL LINE...WITH THE MAIN THREAT SHIFTING TO DAMAGING WIND
AS THE LINE PUSHES ACROSS THE EASTERN PORTIONS OF THE OUTLOOK
AREA OVERNIGHT. SOME DECREASE IN INSTABILITY OVERNIGHT WILL
LIKELY RESULT IN SOME WEAKENING OF STORMS AS THEY MOVE TO THE
EAST. THE POTENTIAL FOR LOCALLY HEAVY RAINFALL WILL ALSO
INCREASE OVERNIGHT...PARTICULARLY ACROSS SOUTHERN PARTS OF THE
OUTLOOK AREA.

GUSTY SOUTH WINDS AHEAD OF THE LOW WILL ALSO PRODUCE GUSTS UP TO
45 MPH PRIOR TO SUNSET THIS EVENING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

THERE IS A CHANCE OF THUNDERSTORMS MONDAY MORNING ACROSS
SOUTHEASTERN PORTIONS OF THE OUTLOOK AREA...MAINLY SOUTHEAST OF A
LINE FROM PONTIAC TO VALPARAISO.

THERE WILL BE ANOTHER CHANCE OF THUNDERSTORMS THURSDAY AND
THURSDAY NIGHT...AND AGAIN SATURDAY NIGHT AND SUNDAY.