How the polar vortex fuels intense winter weather in the US

Here’s how the polar vortex and climate change are affecting extremely cold winter weather in the US.

Intense snowy winter weather in the US has been driven by the activity of the polar vortex that is sliding down to engulf large parts of the country.

The beginning of January’s winter storm added seven states declare a state of emergencywith flights grounded, businesses closed and one area of ​​New York recording 6.25 feet (1.9 m) of snowfall in just 24 hours. Another wave of arctic air has kept temperatures below average through mid-January, and parts of the Midwest to the Appalachians and the Atlantic coast are expecting additional wintry storms.

This blast of cold weather is due to activity in the polar vortex.

The polar vortex, or arctic vortex, is a ring of strong westerly winds that form between 10 and 30 miles (16-48 km) above the North Pole each winter, enclosing a large pool of extremely cold air. The stronger the wind, the more air inside is isolated from warmer areas. When the vortex is stable, the polar jet stream shifts north, helping to keep the coldest air in the Arctic.

But when this stable scenario breaks down, it could mean an intense cold picture in mid-latitudes where the US is located. As the vortex weakens, its wind pattern changes from a circular ring to a wavy band that loops further south. This triggers the cold weather that is normally maintained at the pole further south.

“The (early January) cold snap and that until January 16 is basically broken by pieces of the polar vortex,” Brett Anderson, senior meteorologist at AccuWeather, told the BBC. “(It’s) like a big chunk of ice breaking off a glacier and flowing south with the current — where the current is the jet stream that’s winning.”

It is not known whether climate change will affect the polar vortex, said Amy Butler, an atmospheric scientist at the National Oceanic and Atmospheric Administration and an expert on the polar vortex. There are several reasons why it is so difficult to predict whether polar vortices will strengthen or weaken in the coming years.

“There are many things that can change the strength of the polar vortex,” says Butler. Sea ice is one of them – some models suggest that melting sea ice may have a weakening effect on the eddy. However, heating in the upper atmosphere can potentially strengthen the vortex. Regional changes in sea surface temperatures can also affect the eddy.

“For these reasons, the models show no agreement on what will happen to the Northern Hemisphere polar vortex in the future,” says Butler.

In many parts of the United States, total snowfall has fallen since official records began in the 1930s. The Pacific Northwest and parts of the Midwest have seen a decrease, although the Great Lakes have received more snow in the past—albeit by a modest amount.

One reason for this overall decrease in snowfall is that more winter precipitation is falling in the form of rain instead of snow – and this is due to warmer air temperatures due to climate change. Between 1949 and 2024, more than 80% of weather stations located in the contiguous 48 states have measured a decrease in the proportion of precipitation falling as snow. In addition, snow cover – the area of ​​land covered by snow decreased by an average of 2,083 sq mi (5,395 square kilometers) per year since 1972.

Other changes may also make cold snaps more difficult to prepare for with climate change. “It’s possible that the type of precipitation could change, leading to some regions seeing more snow and other regions seeing more ice or sleet events, which could have greater implications for, say, transportation than snow,” Butler says. “But still other regions could see much less snow, which could strain regions that rely on snowpack for water.” For the western United States, snowmelt gives 75% of the water supply.

There may also be unexpected impacts from climate change. When winter storms do occur, they can sometimes be more intense because of a warmer atmosphere, Anderson says, because a warmer atmosphere can hold more moisture that can fall as precipitation. Snow needs two basic conditions: freezing temperatures and moisture in the atmosphere. And although there are fewer freezes – is winter fastest heating season over most of the United States – Earth’s warming atmosphere now holds more moisture.

“I think with continued warming, especially in the oceans there will be more available energy and moisture for larger winter storms,” ​​adds Anderson, “which may be in the form of extreme amounts of rain or snow. But we’re seeing a trend toward increasing rain or mixed events compared to just snow.”

Anderson points out that he doesn’t have an answer to whether this particular cold outbreak has anything to do with climate change. However, we can expect climate change to continue to cause “short-term variations” in the weather, he says.

Anderson agrees that in the long term, the big picture is clear to see. “There will still be cold and snowy winters in many areas from time to time, but over a long period of time, several decades or more, these cold outbreaks are likely to become even less common,” he says. “Climate scientists focus on the long-term trends (30 years or more) and they all clearly show an undeniable warming trend strongly induced by human activities.”

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