Chicago weather: Dense fog causes headaches for holiday travelers

Dense fog continued on Christmas Eve morning, grounding some last-minute flights out of Chicago for the holidays. 

The National Weather Service issued a Dense Fog Advisory for the entire Chicago area that initially expired at 9 a.m. Sunday but was later extended to 12 p.m. as fog lingered.

Travel out of Midway Airport was put on hold late Saturday night. The FAA issued a ground stop until 10:30 a.m. at Midway Airport. There have been around 50 cancelations so far, with increasing delays. 

O'Hare Airport reported 15 cancelations with minimal delays. 

A spokesperson for Southwest Airlines said visibility remains below required operational minimums, and they have modified their planned start for Sunday at Midway. 

"As a result of the fog at Midway, we have canceled less than 1% of our total flights early on Sunday, 53 out of 4242, throughout our network," Southwest said.

The NWS reminds drivers to use caution on the road during periods of heavy fog. Visibility is at a half mile or less with the fog dissipating throughout the morning.