ASHEVILLE, N.C. (WLOS) — Arctic air is set to sweep across the country this weekend, dropping temperatures below zero in parts of the upper Midwest and bringing a sharp cooldown to the northeast. Even the Southeast will feel the chill as colder air spreads South early next week.
The pattern driving this cold blast begins thousands of miles away over the Arctic.
The polar vortex is a large, swirling circulation of extremely cold air high in the atmosphere above the North Pole. Under normal conditions, strong jet stream winds keep the polar vortex tight and the cold air confined to the far North.
But when the jet stream weakens and becomes wavier, the polar vortex can stretch. That stretch allows pockets of arctic air to escape and dive south because the cold air surrounding it is no longer locked in place…