CHICAGO -- Amid dense fog reducing visibility in Chicago, the Federal Aviation Administration early Tuesday grounded incoming flights at Chicago's O'Hare International and Midway airports through 8 a.m., though the advisory was allowed to expire at Midway and continued at O'Hare after 8 a.m.
For a short time Tuesday morning all flights were grounded, according to the FAA, but as of 7:30 a.m. the agency's website noted the "ground stoppage," or halting of flights, was indicated only for airplanes arriving at the city's two airports. By 8 a.m. flights were arriving and departing regularly at Midway.
Visibility at Midway improved to a mile about 8 a.m. and it still was a quarter-mile at O'Hare, said Casey Sullivan, a meteorologist with the National Weather Service, who noted the dense fog advisory for the city goes through 10 a.m.
"The fog is dissipating from the south," Sullivan said, explaining that's why Midway has resumed air traffic. "The fog is just going to gradually lift across the area during mid- to late-morning hours."
Still, the ground stoppage for incoming flights at O'Hare means not all departing flights will leave on time and travelers could miss connecting flights, leading to a chain-reaction of air travel delays during a traditionally peak period for travel.
"Because a traffic management program is delaying some arriving flights, departing flight schedules may be affected," according to the FAAs Air Traffic Control System Command Center.
As of 8:15 a.m., at O'Hare International Airport 336 flights were delayed, while at Midway Airport 26 flights were delayed. O'Hare reported 23 cancellations and Midway had 71, according to the Chicago Department of Aviation.
The FAA suggests travelers check directly with their airline to determine if a flight has been delayed, and it has a page on its website that provides links to all major airlines. Delays on many airlines at O'Hare were an average of 26 minutes, the city's aviation department noted.
Overnight, "dense, freezing fog" developed throughout the city and its surrounding suburbs, leading to travel difficulties both in the air and on-ground. About 6:30 a.m. visibility at both Chicago airports was less than a quarter-mile, according to National Weather Service meteorologist Mark Ratzer.
"It's pretty soupy out there," Ratzer said. "Visibility is pretty low. There's a few spots where the temperature is freezing and it's possible for a few patchy slick spots, particularly on overpasses."