Throngs of travelers looking to return home after Thanksgiving packed Chicago's Midway International Airport Sunday, causing an unusually long security line that was a mile long, according to local media reports.

“This happens sometimes,” Chicago Aviation Department spokeswoman Karen Pride told Fox 32 News. “There was a period of time earlier this morning, between 6 a.m. and 8 a.m., that lines were long because that is when most people are traveling for the holiday period.”

As of 6 p.m. ET Sunday, 5,861 flights across the U.S. were delayed and 416 were cancelled, according to flight-tracking website FlightAware.com.

One traveler, 21-year-old Emma Cronin, told the Chicago Sun-Times the line stretched through the Chicago airport to the Chicago Transit Authority Orange Line station.

Cronin got to the airport an hour before her flight and said she made it on time. She said security officers were helpful and "the line moved very fast."

In Denver, fog and wind caused delays Sunday, and 46 incoming flights were diverted to other cities.

Most of the diverted flights landed in Colorado Springs, about 90 miles south, Denver International Airport spokeswoman Laura Coale said.

Incoming flights were delayed by about an hour Sunday afternoon, down from two hours earlier in the day. Departures were also delayed but times weren't available.

"It's not turning out to be the best travel day," Coale said.

Weather prevented the use of three of the airport's six runways, Coale said.

A cold front that moved through Denver and other cities on Colorado's Front Range helped create the fog, National Weather Service meteorologist Kari Bowen said.

The temperature dropped 16 degrees in less than 30 minutes at the Denver airport because of the front, she said. In Greeley, about 60 miles north, the temperature fell 21 degrees in 20 minutes.

The Denver airport expected 166,000 passengers on Sunday and 157,000 on Monday as the Thanksgiving weekend wrapped up.

Normally, about 144,000 passengers a day use the airport.

Denver was the fifth-busiest airport in the U.S. last year with 53 million passengers.

Ground traffic was heavy on Interstate 70 through the Colorado mountains on Sunday because of the holiday weekend and fresh snow that drew skiers to resorts, the Colorado Department of Transportation said.

Collisions were causing isolated highway delays.

The Associated Press contributed to this report.