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Polar vortex: What’s behind the lethal winter storm in the United States?

Around 17 states witnessed snowfall, with more than a foot of accumulation in some areas. The deep freeze strained energy supplies in some states, and the National Weather Service predicted widespread, prolonged travel disruptions

4 min readNew DelhiUpdated: Jan 26, 2026 06:15 PM IST

A person carries grocery bags up a residential street during a winter storm in Cincinnati on Sunday. (Photo: AP)

A powerful winter storm triggered heavy snow, sleet and freezing rain from the Ohio Valley and mid-South to New England in the United States on Sunday (January 26), leaving at least seven people dead.

Around 17 states witnessed snowfall, with more than a foot of accumulation in some areas. The deep freeze strained energy supplies in some states, and the National Weather Service predicted widespread, prolonged travel disruptions.

An estimated 157 million Americans were warned against cold ranging from sub-zero temperatures along the Canadian border to below-freezing as ‍far south ⁠as the Gulf of Mexico, according to a report by Reuters.

The storm has been fueled by the activity of the polar vortex, which has expanded southwards.

What is the polar vortex?

The polar vortex is a large area of low-pressure and cold air that swirls like a wheel around both of the Earth’s polar regions. There are two types of polar vortex: tropospheric and stratospheric.

The tropospheric polar vortex occurs at the lowest layer of the atmosphere — it extends from the surface up to about 10 km to 15 km — where most weather phenomena occur.

The stratospheric polar vortex occurs at around 15 km to 50 km high. Unlike the tropospheric polar vortex, the stratospheric polar vortex disappears during the summer and is the strongest during the autumn.

When does the polar vortex cause extreme cold?

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The US, parts of Europe, and Asia experience chilly winds when the polar vortex at the North Pole weakens and travels from its usual position. “As this system weakens, some of the cold, arctic air can break off and migrate south, bringing plenty of cold air with it. Areas as far south as Florida may experience arctic weather as a result,” according to a report in the National Oceanic and Atmospheric Administration (NOAA) SciJinks.

That happens because when the polar vortex is strong and stable, it keeps the jet stream travelling around the planet in a circular path. The jet stream is a narrow band of strong wind in the upper levels of the atmosphere, which plays a key role in keeping cold air north and warm air south.

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“Without that strong low-pressure system, the jet stream does not have enough force to maintain its usual path. It becomes wavy and rambling. When high-pressure systems get in its way, a collection of cold air pushes south, along with the rest of the polar vortex system,” the report added.

Is climate change impacting the polar vortex?

Scientists are still researching the precise impact of climate change on the polar vortex, and whether rising temperatures are making the low-pressure system buckle more frequently.

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Some researchers believe that as the poles are getting warmer at a faster rate than the rest of the Earth, the polar vortex and jet stream are becoming weaker. Warmer temperatures make it easier for the polar vortex and jet stream to get disrupted.

“It makes sense that the polar vortex tends not to be as strong due to global warming because the planet isn’t warming uniformly. It’s warming more at the pole, overall decreasing the strength of the polar vortex and the jet stream and making it more susceptible to being dislodged and sent our way,” Steven Decker, the director of the Meteorology Undergraduate Program at Rutgers University, said in a press statement in February 2024.