Chicago got a brief respite from the sweltering heat Thursday when a huge storm swamped parts of the Windy City during its morning rush hour.

The storm stranded motorists throughout the city and shut down a reactor at a nuclear power plant about 125 miles away.

Parts of Interstate 94 and other expressways were flooded and closed after the skies opened, unleashing a torrential downpour on the Chicago area. Some motorists were briefly stranded in their cars after attempting to drive through flooded underpasses. Firefighters responded to "dozens of 911 calls" from motorists, Fire Commander Will Knight said.

No injuries were reported.

A lightning strike caused a fire in the main transformer at the Quad Cities nuclear plant in Cordova, disabling power lines and causing one of two reactors to shut down automatically, Exelon Nuclear spokesman Craig Nesbit said. The fire was quickly extinguished.

The storm left more than 40,000 people without electricity, and a flash-flood warning was issued for parts of northern Illinois. Chicago's two airports reported two-hour flight delays, and the Museum of Science and Industry was closed because of flooding in its underground garage.

In southern Wisconsin, a deluge — as much as 8.7 inches of rain — flooded roads and cooled heat that the Milwaukee County medical examiner's office listed as a possible factor in the death of a 56-year-old man on Monday.

Thunderstorms were expected in parts of Kansas and Missouri late Thursday, but the current heat wave — the third in the area this summer — was expected to continue, said Mark Mitchell, meteorologist with the National Weather Service in Pleasant Hill, Mo.

The Associated Press contributed to this report.