Polar vortex chill strikes parts of the U.S. again

MINNEAPOLIS, Feb. 25 (UPI) -- Another polar vortex swooped into Minnesota and the Dakotas Tuesday, dropping the already cold temperatures to 10-20 degrees below normal, forecasters said.

The frigid weather is forecast to move through the Midwest and East Coast by midweek, and is expected to affect about two-thirds of the country as it treks across the country, CNN reported.

Waves of colder air were forecast to filter down from the arctic to the northern Rockies, Midwest and Northeast as the week progresses and the polar vortex sinks southward, AccuWeather.com said.

"The polar vortex is essentially a mass of very cold air that usually hangs out above the Arctic Circle and is contained by strong winds," said AccuWeather.com Senior Meteorologist Alex Sosnowski.

In January, a large frigid air mass broke free from the arctic and enveloped North America for days, bringing with it record lows as far south as Alabama.

Although this week's cold air has the same origins as January's massive freeze, the National Weather Service has called it a "cold mass of arctic air."

AccuWeather.com said one or more disruptive snowstorms could travel from the Rockies to the Plains to the East Coast later in the week and into the weekend.