(CBS) – Foggy conditions temporarily shut down Chicago’s Midway Airport on Thursday.

The city’s Aviation Department announced a “ground stop” at the Southwest Side airport at 4:30 p.m., but flights were operating again, with delays of 30 minutes or more, in the evening. More than 180 flights were canceled.

At O’Hare, which continued operating Thursday, delays also were 30 minutes or more on Thursday evening. More than 420 flights were canceled.

Travelers were urged to check with their airlines for the latest information.