Thunderstorms will last through the evening, and then on Sunday, hot temperatures will return, with the heat index between 100 and 105 degrees. A flood watch is in effect as a threat of severe storms is expected by the afternoon for the Chicago area.

As of 12:30 p.m., heavy rain had already started to fall in some parts. A flash flood warning was in effect for DuPage and Cook County, the NWS said, with reports of "totally submerged viaducts and underpasses in the city of Chicago."

Flood Watch issued for most of Chicagoland until 7 p.m. Saturday. Heavy rain is possible tonight and tomorrow. 3:18 p.m. - Flood Warning issued for DuPage, Cook Counties until 5:30 p.m.Ground delays issued at O'Hare, Midway airports due to storms. Average delay is 75 minutes, according to the FAA.