Meteorologists had predicted that parts of the U.S. would experience the 10th and coldest polar vortex event this season. Weather forces in the Arctic are pushing chilly air that usually stays near the North Pole into the U.S. and Europe.

Harsh weather moved west as a polar vortex was expected to grip the Rockies and the northern Plains after winter storms pummeled the eastern U.S. over the weekend.

Bitter cold has descended on swathes of the US this week, as the nation faces its 10th – and coldest – polar vortex of the season. In a normal winter, you can expect to see this happen two or three times.

The term “polar vortex” usually refers to the gigantic circular upper air weather pattern in the Arctic region. It is a normal pattern that is stronger in the winter and keeps some of the coldest weather bottled up near the North Pole.

The latest arctic blast will move into the northern Rockies and northern Plains Saturday and spread to the central and eastern U.S. through much of next week.

An Arctic blast tied in part to the polar vortex is driving record frigid air south from the Northern Plains toward the Gulf Coast Tuesday in a cold snap that will last the entire week. Threat level: This event is forecast to set records for the coldest temperatures on record for this late in the season,