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

According to the National Weather Service, a polar vortex will impact most of the country this weekend, here is what you need to know.

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.

Despite a cold start to the day, most of the U.S. will experience seasonably mild temperatures on Thursday. However, dangerous changes are on the way as a polar vortex tightens its grip on the nation as sends temperatures tumbling below freezing starting this weekend.

The freezing temperatures will move eastward, reaching locations like Philadelphia, where daytime highs will only reach the upper teens. The polar vortex is a gigantic circular upper-air weather pattern in the Arctic that envelops the North Pole.

In Indiana, around zero degrees was likely, the map showed, with temperatures of around three degrees possible in Northern Maine. Northern Georgia would see temperatures around 16, and in Colorado, the map showed that some areas would see -9.