Weather Explainers

What is the Polar Vortex?

The polar vortex is an area of low pressure in the upper atmosphere, primarily in the stratosphere, a layer of the atmosphere above which most of our sensible weather occurs (known as the troposphere).

Example configuration of a strong polar vortex near the North Pole.

Breaking the term in two: "polar" means it resides in the higher latitudes, both near the North and South Poles; "vortex" means it is a closed circulation surrounding the polar regions.

Don't be confused: It is not a storm, like a winter storm or blizzard; instead, it's a standard feature of the Earth's atmosphere. It is semi-permanent, meaning it is not something new, and was not "discovered" in January 2014. It has been around likely as long as there has been weather on Earth. According to The Weather Channel senior meteorologist Stu Ostro, the term was even used before the Civil War.

The polar vortex is strongest in winter, thanks to an increased temperature contrast between the polar regions and the mid-latitudes, including the United States.

The Northern Hemisphere polar vortex frequently, but not always, has centers in two main areas: near Canada's Baffin Island, and over northeast Siberia. There is a Southern Hemispheric version of the polar vortex, as well, within which depletion of the upper-atmospheric ozone layer occurs.

The polar vortex and the impact on your weather is opposite of what you'd think. Here's how it works: When the polar vortex is strongest, you're less likely to see cold air plunge deep into North America or Europe. (By strongest, we mean the generally west-to-east flow around the vortex is stronger than average.)

Example of a weakened and elongated polar vortex due to stratospheric warming over Alaska and northeast Siberia.

The easiest way to conceptualize this is in terms of a wall. A stronger polar vortex effectively helps to wall off cold Arctic air from the mid-latitudes.

Occasionally, though, the polar vortex is disrupted and weakens. This happens when the stratosphere warms.

NASA's Goddard Space Flight Center has a more technical explanation for sudden stratospheric warming.

When the polar vortex is weakened a piece of the polar vortex can surge farther south, bringing Arctic cold into portions of North America and Europe.

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