Fog delays over 400 flights in Chicago on one of the busiest travel days of the year

Thanksgiving travelers are encountering cancellations and delays at Chicago's airports as extremely dense fog settles over the region.

According to flightstats.com, 90 inbound and outbound flights were canceled and more than 400 were delayed at O'Hare and Midway airports as of around 7:45 a.m.

National Weather Service meteorologist Richard Castro says visibility has been near zero at both airports for about two hours.

O'Hare serves as a hub for the nation's air system and is traditionally the busiest airport in the country for Thanksgiving travel.

The Chicago Department of Aviation says it expects 1.8 million passengers to move through the two airports in the week between Nov. 20 and Nov. 27. Sunday is expected to be the busiest day, when O'Hare alone could see more than a quarter million travelers.