A blast of Arctic air is set to cover much of the United States with temperatures below freezing starting on Friday and into next week, impacting millions of Americans in nearly all of the contiguous states.

Temperatures will reach below 10 degrees Fahrenheit in the Northern Plains and Upper Midwest, into the teens in the central Plains and Midwest and near 30 degrees in parts of the South on Saturday, before the front moves into the East Coast and the Southeast on Monday, the National Weather Service said.

Americans living as far south as the Southern Plains can expect to see sub-zero wind chills beginning Sunday night, said Zack Taylor, a meteorologist with the National Weather Service’s Weather Prediction Center.

“That will actually linger for several days for much of the southern U.S., Ohio Valley, mid-Atlantic and the Northeast as we get into early to mid-next week,” he said.

The coldest weather of the season to date will be due to a phenomenon called a polar vortex, an upper-level jet stream that typically circulates around both the North and South Poles, but can push cold winds down into the U.S. and Canada when it weakens and expands.

The bitter cold temperatures will bring “life-threatening” risks of hypothermia and frostbite, the NWS warned.

President-elect Donald Trump said on Friday his inauguration will be held indoors on Monday because of severe cold. Temperatures are forecast to be only as high as 23 degrees on Monday in Washington, D.C., with wind chill set to make it feel even cooler.

States from Virginia up into New England could see heavy snow along with frigid temperatures, with Washington, D.C., Baltimore, Philadelphia, New York City and Boston potentially receiving several inches of snow.

Southern states could also get snow and ice from a separate storm starting Monday night across portions of Texas that may spread as far south as the Gulf Coast, said Taylor.

“That’s something that we are keeping a close eye on, given the sensitivities of those not accustomed to winter weather and not used to those kind of situations,” he said.