UPDATED 06/08/11 6:52 p.m.

CHICAGO (STMW/CBS) — Just before a 30-degree drop swoops in to cool off the area, Chicago and Northwest Indiana residents will have to put up with thunderstorms that could bring damaging wind gusts up to 60 miles per hour Wednesday night.

But the cooling won’t happen so fast.

“It’s not going to be a quick, dramatic drop but I think overnight we’re going to probably go from 95 degrees to about 80 into late evening. If it rains and gets cooler, we’re going to fall back into the 60s overnight,” National Weather Service meteorologist Mike Bardou said.

The drop will all depend on when a cold front approaches from the northwest. The current airmass will stay hot, then gradually drop off in the 80s as darkness approaches. By about 10 p.m., the storms should cool off the area and drop to about 60 degrees about 3 a.m., Bardou said.

The anticipated storms could produce quarter-size hail, frequent cloud-to-ground lightning, more than an inch of rainfall and wind gusts in excess of 60 mph, the National Weather Service said.

With the rain comes a cold front which the weather service calls a “very unstable” airmass. Thunderstorms will become organized into a line and may bring multiple rounds of heavy rain. Localized flash flooding, mainly in urbanized or poor drainage areas, will be a concern Wednesday night, the weather service warns.

The storms will mainly affect north central Illinois, northeast Illinois and Northwest Indiana. That includes Cook, DuPage, Will, Kankakee, DeKalb, Kane, McHenry and Lake counties in Illinois, and Porter, Newton, Jasper and Benton counties in Indiana.

Thursday’s high will reach just 63 degrees and there will be a 40 percent chance of thunderstorms. The low will dip to 54 with a 69 percent chance of storms, the weather service said.

“You’ll probably head to work with it being in the 60s and by the time you leave on Thursday, we’ll reach the upper 50s, especially downtown and warmer inland,” Bardou said.

Those storms may be severe with damaging winds and large hail possible Thursday afternoon, just south of I-80. There’s also a chance of severe thunderstorms Friday afternoon and evening.
The weekend should be sunny, with a high of 74 degrees on Saturday and 70 degrees on Sunday.

© Sun-Times Media Wire Chicago Sun-Times 2011 & CBS contributed to this story. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed

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