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.

An arctic blast will send temperatures across the United States plummeting as bitterly cold air that originated in Siberia will arrive from Canada by week’s end, bringing with it dangerously cold wind chills for millions of Americans.

A potent shot of Arctic air starts settling in Monday as a massive dip in the jet stream pulls in frigid air across the entire eastern half of the country. Temperatures are set to drop as low as 20 degrees below average Tuesday and Wednesday with highs only reaching the teens, with lows in the single digits and even plunging below zero.

The president-elect announced that Monday’s ceremony will be held inside the Capitol, leaving thousands of people rushing to make new plans.

President-elect Donald Trump said his inauguration on Monday will take place inside the U.S. Capitol rather than outdoors because of severe cold, the first time in 40 years that U.S. presidential inaugural ceremonies will be moved indoors.

President-elect Donald Trump’s inauguration will be moved indoors due to frigid temperatures expected for Monday, the incoming commander in chief said on Friday. “There is an Arctic blast sweeping the Country.