The National Weather Service warned drivers to slow down, use headlights and leave plenty of distance between vehicles this morning because of dense fog.
A dense fog advisory was in effect until 9 a.m.
Visibility could be reduced to a quarter of a mile or less, the weather service said. That could create hazardous driving conditions during the morning commute on Interstates 80, 94, 90 and 65.
A number of school districts were on delays Thursday morning. For a list, click here.
The fog was expected to dissipate by mid-morning. Clouds could give way to sun later Thursday, and temperatures could rise into the high 70s.
Forecasters were predicting a weekend warm-up, with highs in the mid-80s Saturday and Sunday. There was a chance of showers and thunderstorms, mainly after 1 p.m. Sunday, according to the weather service.