An estimated 2.4 million passengers are expected to travel through Chicago's airports over the holidays.
The holiday travel period runs from Dec. 21 through Jan. 2, according to the city's Department of Aviation.
Already the winter storm was having an impact Thursday. More than 450 flights were canceled and others delayed at Chicago's airports due to the weather. The majority of Southwest flights scheduled for Thursday afternoon and night to and from Midway have been canceled, the airline said on its website.