Polar vortex explained – graphic credit: National Oceanic and Atmospheric Administration (NOAA)

A system previously unknown to most people, the polar vortex is a large area of low pressure and cold air surrounding the Earth’s North and South poles. The term vortex refers to the counter-clockwise flow of air that helps keep the colder air close to the poles (see left globe in graphic). Often during winter in the Northern Hemisphere, the polar vortex can become less stable and expand, sending cold Arctic air southward over the United States with the jet stream (right globe), reports the National Oceanic and Atmospheric Admin (NOAA).

When the polar vortex is at its strongest, it’s also well-organized – that is, a kind of hurricane-like structure that circles tightly just where its name suggests, at the pole. It’s only as the system weakens that it stumbles. A disrupted vortex can stumble, wobble, and split or shift far from the pole.

Emerging research suggests that a warming Arctic is causing changes in the jet stream and pushing polar air down to latitudes that are unaccustomed to them and often unprepared. Hence this week’s atypical chill over large swaths of the Northeast and Midwest, according to The New York Times. Temperatures in the upper…

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