The atmosphere is preparing to send part of the polar vortex southward toward the United States next week with an outbreak of arctic air and lake-effect snow.
The polar vortex is a large pocket of very cold air, typically the coldest air in the Northern Hemisphere, which sits over the polar region. Occasionally, this pocket of very cold air can get dislodged farther south than normal, leading to cold outbreaks in Canada and the U.S.