The FAA grounded incoming flights to O’Hare and Midway until at least 8 a.m, according to the Chicago Tribune. The Weather Channel predicted that “fog may lead to significant delays in parts of the Midwest, including at Chicago’s O’Hare and Midway airports.” The National Weather Service, meanwhile, issued a dense fog advisory for Chicago, in effect until 10 a.m CST. “Areas of dense fog reducing visibility to one quarter mile or less,” the forecast stated. “Temperatures in a few spots will drop below freezing in spots and could lead to isolated icy patches on untreated elevated surfaces.” The advisory affects Winnebago, Boone, McHenry, Kane, DuPage, and Cook Counties.

“It’s pretty soupy out there,” National Weather Service meteorologist Mark Ratzer told the Chicago Tribune. “There’s a few spots where the temperature is freezing and it’s possible for a few patchy slick spots, particularly on overpasses.”

The FAA’s Air Traffic Control System Command Center website stated that a traffic management program was in effect for O’Hare and may delay departing flights. “Due to EQ:FAA, traffic is experiencing Gate Hold and Taxi delays between 16 minutes and 30 minutes in length and increasing,” the command center stated, noting that gate holds and taxi delays caused about 15 minute delays at Midway. “Arrival traffic is experiencing airborne delays of 15 minutes or less,” the sites for both Midway and O’Hare reported.

Over 100 flights have been canceled between both Chicago airports. As of 10:11 a.m., delays at O’Hare averaged 32 minutes, and Midway delays averaged less than 15 minutes. There were 49 cancellations at O’Hare and 71 at Midway, according to the Chicago Department of Aviation.

There should be few major travel issues in the windy city on Wednesday, according to The Weather Channel, but light snow or rain may affect parts of the upper-Midwest and northern Great Lakes on Thursday.

AAA reported that 115.6 million Americans are expected to travel during the 2019 holiday season, the most since AAA started tracking in 2000. The worst day to travel in Chicago is expected to be December 26, with a peak congestion period between 4:45 p.m. and 6:45 p.m. Nearly 7 million Americans are expected to fly by January 1, the most since 2003.

The FAA did not immediately respond to request for comment, and the Chicago Department of Aviation declined to comment on the record.