Many motorists were not able to see road signs, stoplights or railroad crossings until the last minute. Drivers were advised allow extra travel time, reduce speed and keep a safe distance to avoid accidents.
As of 10:50 a.m. Wednesday, the Chicago Department of Aviation said O'Hare International Airport had delays averaging 45 minutes for flights heading to the San Francisco area due to fog in that area, and there were some delays and more than 90 flights canceled at Midway International Airport due to fog.
Several city landmarks were shrouded in heavy, white fog, making for an eerie sight.
The fog is expected to dissipate over the course of the day. In the afternoon, skies will be partly-to-mostly cloudy. High temperatures will be near 70 inland and near 60 by the lake. Thunderstorms are expected in the evening.