A polar vortex dipping down from Siberia is bringing a cold front with frigid temperatures to millions Americans. See maps of the arctic blast.

An Arctic blast that began in the northern plains on Saturday spread bitter cold from the Rockies through the East Coast and as far south as Florida by Tuesday morning. A blizzard warning was in effect for southern Louisiana, the furthest south such a warning has ever been posted.

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.

How the Polar Vortex Can Bring Arctic Blasts to the U.S. Vast weather patterns can carry blasts of frigid air far from the polar regions—here’s how it works

Most of the U.S. will enjoy milder temperatures on Thursday, but the warmup will be brief as a polar vortex will send temperatures tumbling below freezing for most of the nation starting this weekend.

A series of disturbances in the atmosphere is sending the polar vortex south (again) next week with a burst of even colder Arctic air than last week.

A series of cold fronts the last few weeks has kept Florida downright chilly, as another winter storm starts to take aim this weekend