Millions of Americans are dealing with freezing temperatures on the first day of winter.
The National Weather Service is warning of a powerful winter storm that will produce various hazards across the central and eastern U.S. through the end of the week.
Arctic air is forecasted to begin diving southwards on Wednesday.
"This will not be your average cold front as temperatures could drop 20 or more degrees within a few hours," the National Weather Service says.
Denver is expected to reach a high temperature of -2 on Thursday.
In addition to bitterly-cold temperatures, a large portion of the middle of the country will see light-to-moderate snowfall. Blizzard conditions are forecasted for the central and northern Plains. The Great Lakes could see up to a foot of snow between Wednesday night and Friday, according to the National Weather Service.
Storms are expected to make their way eastward by Friday.
There's major fear the storms will severely impact holiday travel.
United is waiving its change fee and any difference in fare on qualifying tickets for flights departing on or before Dec. 28 at many U.S. airports due to the winter weather.
American Airlines is waiving change fees on qualifying tickets for those who plan to fly over the holidays at the 29 listed airports in the northeast that could be affected by winter weather.
Southwest issued a travel advisory for airports in the midwest, adding that those with qualifying tickets traveling Wednesday through Monday could rebook their flights "without paying any additional charge."
While much of the storm will impact a large portion of the central and northeastern part of the U.S., the South isn't out of the woods. Below-zero wind chills are forecasted through the end of the week.