What is a polar vortex? What to know about the weather phenomenon

The polar vortex is slated to sweep across parts of the Midwest this week, bringing with it harsh conditions, forecasters have warned.

The polar vortex refers to the cold air and low pressure that constantly surrounds both of the Earth’s poles. In the winter, a disruption in the polar vortex can occur as it tends to expand in the northern hemisphere, pushing that cold air further south, according to the National Weather Service (NWS).

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Read on for a look at what to know about the polar vortex and how it could impact this winter’s weather.

What is a polar vortex?

A polar vortex “is a large area of low pressure and cold air surrounding both of the Earth’s poles,” the NWS explains. In the northern hemisphere, the vortex tends to expand in the winter, pushing the colder air south.

The boundary between the colder air coming down from the Arctic and the warmer air from the south is called the polar front jet stream, which usually moves quickly from west to east, according to Mark Serreze of the National Snow and Ice Data Center. That boundary line is continually moving – generally shifting further south in the winter.

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"Aside from temperature, the very important thing about where the jet stream lies is that storms (like nor'easters) form along the jet stream and their path is guided by the jet stream," Serreze told Fox News, adding the temperature contrast of the warm and cold air "is what feeds the storms."

The vortex is continuously present – whether we feel the effects or not.

Is it dangerous?

While the name seems menacing, the greatest danger a polar vortex brings is a decrease in temperature as it expands – particularly in areas that don’t normally experience drastically cold weather.

Is it new?

No. Polar vortexes have been occurring for a long time, albeit the term “has only recently been popularized,” according to the NWS.

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The Weather Channel meteorologist Stu Ostro has said the term was even used before the Civil War.

Does climate change play a part?

The effect climate change has on the polar vortex is still up for debate among climate scientists, Serreze said.

"Nobody is questioning the strong Arctic warming. Where the questions lie are the effects of the warming on the polar vortex and jet stream," he said. "While some scientists argue that the Arctic warming is already having an effect on the polar vortex and jet stream (hence weather patterns), other scientists remain unconvinced and focus on other things that can affect the jet stream, such as sea surface temperatures in the tropics."