SEATTLE (NewsNation) — A major winter storm is expected to cause travel disruptions for millions of holiday travelers, with hundreds of cancellations and delays already plaguing airports across the nation.

As of 6 a.m. Tuesday, there have been over 400 flights canceled and nearly 300 flights delayed, according to FlightAware.

A winter storm warning with very cold temperatures has been issued for the city of Seattle and much of Western Washington through Tuesday.

Heavy snow on Monday evening influenced the city of Seattle to send out an alert urging people to avoid travel on Tuesday if possible, informing them that emergency shelters were open.

Officials said the heaviest snow will fall Tuesday. Snow in the mountains could continue into Wednesday.

The weather service said people should plan on difficult travel with potentially hazardous conditions. Heavy snow, poor visibility and whiteout conditions prompted officials to tweet that the Washington State Patrol would be enforcing vehicle chain requirements.

The system is forecast to evolve into a major winter storm and blizzard for the Midwest later this week. Meteorologists anticipate the storm will greatly strengthen over the middle of the nation at midweek and could shut down travel over a number of Midwest cities and states from Thursday to Friday.

According to the American Automobile Association (AAA), 2022 is anticipated to be the third busiest year for holiday travel since AAA began tracking in 2000.

AAA estimates that nearly 113 million Americans plan to travel between Dec. 23 and Jan. 2 — an increase of 3.6 million people over last year and closing in on pre-pandemic numbers. Plus, 102 million Americans are expected to drive to their holiday destinations as gas prices are on track to drop below $3 per gallon by Christmas.

Flights at Seattle-Tacoma International Airport were delayed and canceled throughout Monday. Nearly 500 domestic flights in and out of the airport had been delayed, with 33 total cancellations, according to FlightAware, an online tracker.

As of 6 a.m. Tuesday, there have been 170 flight cancellations and 33 delays in and out of Seattle-Tacoma International Airport alone.

The airport remains open and stated on its website that it is aware of the storm and “snow ready.”

“Snow is in the forecast, and our team is ready to roll—literally! That means removing snow and ice from the airfield and runways and plowing and de-icing the parking garages,” the official account for Seattle-Tacoma International Airport tweeted.

While the airport remains open, it urges travelers to regularly check flight statuses and information.

Alaska Airlines said it has also canceled roughly 100 flights on Tuesday, “with more cancellations possible, depending on the weather,” KOMO-TV reported.

Updated winter travel information for motorists can be found on the Washington Department of Transportation website.

The Associated Press contributed to this report.