Something strange is happening above the North Pole. A phenomenon that could cause the polar vortex to disintegrate faster than ever recorded, causing a sudden cold snap in parts of the Northern Hemisphere.
But another unprecedented force is also at work: the historically strong El Niño event, which typically causes global temperatures to rise. It’s sparking an atmospheric battle for influence over our weather, but it’s not yet clear who will win.
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The polar vortex is a band of strong winds high in the atmosphere that tightly wraps the frigid air in the Arctic and traps it around the North Pole. They form each fall when the sun sets over the top of the world and the dark arctic night begins.
Although it exists in the stratosphere about 16 to 30 miles above the Earth’s surface, it can play a strong role in shaping winter weather patterns in the Northern Hemisphere.
The polar vortex has been weakening in recent weeks. Currently, the stratospheric atmosphere is warming dramatically due to a phenomenon known as “massive sudden stratospheric warming,” when the polar vortex winds reverse. In the days to weeks after this happens, arctic air could flow into the Northern Hemisphere from the south, favoring the development of cold air.
“This is a very unique year,” said Andrea López Lang, a meteorologist at the University of Wisconsin-Madison. Large-scale stratospheric warming events typically occur between January and March, with the earliest previous events occurring on November 28 in both 1968 and 2025.
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It is not yet clear why such disruption occurred so quickly. It’s possible that El Niño played a role. Some studies have linked El Niño to a weakening of the polar vortex and more frequent large-scale disturbances. “But we don’t know yet,” says Simon Lee, an atmospheric scientist at the University of St. Andrews.
What is certain is that its unprecedented nature makes it difficult to understand exactly where and how the impact will play out. “Basically our historical events don’t capture what’s actually happening because it’s happening so early in the season,” López-Lang said.
The United States and parts of Europe will get their first taste of winter this week with a cold snap that may be linked to the polar vortex disruption.
Arctic air spills into North America and Europe on Wednesday and is expected to continue into the weekend, with cold temperatures peaking in most regions on Thursday or Friday. This means widespread frost, the first for many parts of the eastern United States and northwestern Europe.
The cold weather is not expected to be particularly extreme, but regions such as the East Coast of the United States and the United Kingdom will see a sharp departure from the unusually warm summer and fall.
Most of the United States east of the Mississippi River is experiencing its first cold snap since spring, with most of the eastern half of the country expected to endure temperatures between 7 and 14 degrees Fahrenheit below average for mid-November. Similar extreme cold temperatures will also affect northern Europe.
However, the cold snap will not last long, with above-normal temperatures expected to return to the eastern United States and other parts of the country next week.
Judah Cohen, a climatologist at the Massachusetts Institute of Technology, said this week was just an “appetizer” and the more impactful “main course” may still be yet to come. He said the effects of the disruption typically take several weeks to subside, and there is an increased risk of cold weather in both eastern North America and northern Europe in late November and early December.
Polar vortex disruptions do not automatically lead to deep freezes. This is especially true if it occurs early in the season, before the arctic cold sets in, or if we have to deal with a super-sized El Niño.
López-Lang said El Niño is a “big bully that pushes the atmosphere in a certain direction.” She believes the impact will be “so overwhelming” that while we may see some colder weather, it won’t be anything beyond what we would expect during a typical winter season.
Amy Butler, a research physicist at NOAA’s Chemical Sciences Institute, agrees. “The striking feature for me over the next month is that temperatures are likely to increase in the northern half of the United States, possibly related to El Niño,” she said.
Some people disagree. “There’s a common belief that El Niño is like a runaway freight train, and there’s nothing to stop it,” says MIT’s Cohen. That’s important, he added, but “whether we have cold air depends on the movement of the polar vortex.”
Jason Furtado, an associate professor of meteorology at the University of Oklahoma, said the effects of global warming also need to be considered. Winters are on average warmer than they were just a few decades ago. “So when you’re talking about the potential for cold weather, it’s all relative,” he says.
NOAA’s Butler said the polar vortex appears to be rapidly re-intensifying after this event. “This disruption may not have much staying power,” she says.
However, further polar vortex disruptions may occur in the future. “I wouldn’t be surprised if we see another sighting this winter,” López-Lang said. “And the next one might be the one that really affects us.”
This unique winter will give scientists a chance to see if El Niño is controlling the weather, or if the polar vortex can still exert its full force.
“It’s starting to feel like an experiment,” López-Lang said. “I think it’s going to be really exciting to watch.”
CNN’s Andrew Friedman contributed reporting.
