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Dublin: 5 °C Sunday 8 December, 2019

What is the 'polar vortex' sweeping across the US, and how did it form?

The weather system is sweeping across the States right now causing temperatures to drop to dozens of degrees below 0.

AS TUNDRA-LIKE temperatures and wind chills as cold as 70 below zero fan out across the United States, everyone is blaming the “polar vortex”.

Polar vortexes, though, are nothing new. They occur seasonally at the North Pole, and their formation resembles that of hurricanes in more tropical regions: fast-moving winds build up around a calm center.

Unlike a hurricane, these are freezing polar winds, circling the Arctic at more than 100 miles per hour. The spinning winds typically trap this cold air in the Arctic.

Splits apart

The the problem comes when the polar vortex weakens or splits apart, essentially flinging these cold wind patterns out of the Arctic and into lower latitudes.

NOAA scientists have suggested that warming temperatures in the Arctic may be responsible for the weakening of the polar vortex. When the vortex weakens, it’s more likely to break apart and become a factor in our winter weather.

A 2009 vortex breakdown drove temperatures in parts of the Midwest down to -22F. Here’s a NASA illustration of the polar vortex (left) and it splitting in two (right):


Click here to view a larger version. (Image Credit: NASA Earth Observatory)

It won’t just feel like Arctic temperatures in parts of the United States this week — the weather system is actually Arctic air invading from the north.

Of course, the idea that the polar vortex is responsible for the current cold snap is a strong theory, not a fact. As NOAA notes: “Many factors, including random chaos in the development of weather patterns, can produce such extreme winter events.”

- Lauren F Friedman

Read: US prepares for ‘polar vortex’ which could plunge temperatures to -51 degrees Celsius >

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