O'Hare has already canceled more than 150 flights, according to the Department of Aviation.
The city got about two inches of snow overnight, and frigid weather was expected on Tuesday.
After the Thanksgiving debacle at Midway, the TSA said lines would move swiftly at both airports.
The Sept. 27 competition benefits non-profit Special Olympics Illinois.
Full service was restored about 2 p.m., CTA officials said.
CTA officials announced the train involved in Monday's crash was removed earlier today.
On Tuesday, multiple lawsuits were filed in connection with the crash.
Speaking in Mount Greenwood, Garry McCarthy said reducing crime was about more than sheer numbers.
Alexis Prokopchuk of Oakbrook Terrace took the animal on the "L" and abandoned it at O'Hare, police said.
More than 1,200 flights canceled as city deploys plow fleet and prepares schools for below-zero weather.
The footage helps solve the mystery about how an alligator ended up at O'Hare Airport on Nov. 1.
Gogo, a leader in in-flight Internet access, moved its corporate headquarters to Chicago.
Opening O'Hare's new runway, Mayor Rahm Emanuel pointed to Midway Airport as an example of success.
Trains stopped operating beyond Rosemont due to the derailment Monday morning, the CTA said.
The student from China paid $4,240 for a ride from O'Hare to Champaign, which should cost less than $300.
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