A vast, intense winter storm is disrupting travel plans ahead of the Christmas holiday.

As of midday, more than 1,700 U.S. flights had been canceled Thursday, and over 2,600 others had been delayed, according to the flight tracking website FlightAware. More than 800 flights had already been canceled for Friday.

Forecasters predict an onslaught of heavy snow, ice, flooding and powerful winds from Thursday to Saturday in a broad swath of the country, from the Plains and Midwest to the East Coast. A surge of Arctic air will follow. The Christmas weekend could be the coldest in decades.

The National Weather Service said Wednesday the storm was so large and encompassing that around 190 million people are currently under some type of winter weather advisory.

Chicago and Denver were being hit the hardest by Thursday’s flight cancellations. Chicago O’Hare Airport had 231 departing flights and 265 arriving flights canceled, according to FlightAware. Chicago Midway Airport had 112 outbound flights and 132 incoming flights called off. Two hundred seventeen flights scheduled to depart from Denver International Airport were canceled, as well as 214 incoming flights. 

Chicago, which is under a winter storm warning through Friday night, was expected to see up to 4 inches of snow and wind chills plummeting to -15 degrees Thursday, according to the National Weather Service. In Denver, which is under a wind chill warning into Friday, it was -21 degrees at 10 a.m. local time, with a wind chill of -38. 

Detroit Metro Airport and New York’s LaGuardia Airport account for the most cancellations for Friday. There were 100 outgoing and 94 incoming flights canceled in Detroit. LaGuardia had 92 departing and 75 arriving flights nixed.

Rain and snow are expected to move into Detroit overnight, and winds could gust as high as 33 mph, the National Weather Service forecast says. The city is under a winter storm warning through Friday night.

Rain is expected in New York, too, and the city will be under a wind advisory from Thursday night to Friday night, with gusts as high as 46 mph expected.

Because of the weather, airlines are offering waivers on change fees and fare differences for certain flights. 

Some travelers have been trying to beat the weather. 

Jean-Paul Blancq got to Boston's Logan Airport a day early for his Thursday flight home to New Orleans. Blancq had to take a bus to Logan from his seasonal job in New Hampshire and was unsure of the storm's path.

“I hope that my flight doesn’t get canceled because I don’t know what I’ll do,” Blancq told The Associated Press.

Kelli Larkin arrived Wednesday from Florida for a holiday trip to New York. She plans to fly back Saturday night but said she'll watch the forecast and change her return flight if she has to.

“It's a little concerning," she told the AP. “We've got to play it by ear."

The weather also will wreak havoc on car, bus and train travel. Drivers could encounter slick roads and poor visibility. 

Auto club AAA forecast earlier this month that 112.7 people will travel at least 50 miles from home from Dec. 23 to Jan. 2 — an increase of 3.6 million from last year. Nearly 102 million were expected to travel by car, and more than 7 million were expected to fly.

President Joe Biden on Thursday encouraged people who are traveling to take precautions, including by leaving before the storm hits their region.

“I encourage everyone … to please heed the local warnings,” he told reporters at the White House. “ … This is not like a snow day when you were a kid. This is serious stuff.”

As of late Wednesday, Amtrak had canceled train service on around 30 routes, some through Christmas Day. Greyhound canceled bus service on 25 routes for Wednesday and Thursday.

The Associated Press contributed to this report.