In the atmosphere above the Arctic, something strange is happening: the polar vortex has collapsed earlier than ever, a phenomenon that can trigger a cold snap in parts of the northern hemisphere.
However, there is also another unprecedented force at work in the form of a historically strong El Niño, which typically causes global temperatures to rise. This sets up an atmospheric battle to influence our weather – and we don’t yet know who will win.
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The polar vortex is a belt of strong strong winds in the atmosphere that tightly envelop the frigid Arctic air, keeping it trapped around the North Pole. It forms every fall as the sun sets over the top of the world and the dark arctic nights begin.
Although it exists in the stratosphere, between 10 and 30 miles above the Earth’s surface, it can play an important role in shaping the Northern Hemisphere’s winter weather patterns.
In recent weeks, the polar vortex has been weakening. Currently, the air in the stratosphere is warming significantly, in a phenomenon known as “sudden major stratospheric warming,” during which the polar vortex winds reverse. In the days and weeks that follow, Arctic air can spread southward into the Northern Hemisphere, stacking the dice in favor of cold air outbreaks.
“This year is exceptionally unique,” said Andrea Lopez Lang, a meteorologist at the University of Wisconsin-Madison. Major stratospheric warming events typically occur between January and March, with the previous earliest event occurring on November 28 in 1968 and in 2025.
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It is not yet clear why this disruption occurs so early. It’s possible that El Niño played a role – some research has linked it to a weaker polar vortex and more frequent major disturbances. “But we’re not sure yet,” said 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 how and where the impacts will occur. “It’s happening so early in the season that our historical events don’t reflect what’s actually happening,” Lopez Lang said.
Parts of the United States and Europe will get their first taste of winter this week, with a wave of cold conditions that could be linked to the polar vortex disruption.
A blast of arctic air spread across North America and Europe on Wednesday, which will last through the weekend – with a cold peak on Thursday or Friday for most places. This will bring widespread frosts, the first in much of the eastern United States and northwestern Europe.
This cold isn’t expected to be particularly extreme, but it will be a clean break from the unusual heat of summer and fall in places like the US east coast and the UK.
In the United States, almost everywhere east of the Mississippi River will experience the coldest weather since spring, with most of the eastern half of the country experiencing temperatures about 7 to 14 degrees Fahrenheit below mid-November averages. Similar abnormal cold will also affect Northern Europe.
This cold snap won’t last long, however, with above-average temperatures expected to return to the eastern United States and other areas next week.
This week may be just an “appetizer,” with the most impactful “main course” coming, said Judah Cohen, a climate scientist at MIT. The effects of a disturbance typically take a few weeks to be felt, and there is an increased risk of colder weather in eastern North America and northern Europe in late November or early December, he said.
Polar vortex disruptions do not automatically translate into intense cold, especially when they occur earlier in the season, before Arctic cold has had a chance to really develop – and when a full-blown El Niño has to be contended with.
El Niño is “the big tyrant that pushes the atmosphere in a certain direction,” Lopez Lang said. She thinks its impact will be “so huge” that while we may see some cold air, it’s unlikely it will be anything other than what would be expected during a typical winter season.
Amy Butler, a physics researcher at NOAA’s Chemical Sciences Laboratory, agrees. “What strikes me next month is the higher risk of warm temperatures in the northern half of the United States, likely related to El Niño,” she said.
Some disagree. The assumption is that “El Niño is sort of a runaway freight train, and nothing is going to stand in the way of it,” said MIT’s Cohen. That’s important, he added, but “whether cold air is present or not will depend on how the polar vortex behaves.”
The impact of global warming also needs to be considered, said Jason Furtado, an associate professor of meteorology at the University of Oklahoma. Winters are on average warmer than they were a few decades ago. “That means everything is relative when we talk about a possible cold air outbreak,” he said.
It appears the polar vortex will strengthen again quickly after this event, NOAA’s Butler said. “This disruption may not have much staying power,” she said.
But there could be more polar vortex disruptions to come. “I wouldn’t be surprised if we saw another one this winter,” Lopez Lang said. “And the next one could be the one that we actually experience the impacts of.” »
This unique winter will give scientists the opportunity to see whether El Niño controls the weather or whether the polar vortex can still flex its considerable muscles.
“The atmosphere is preparing to become an experience,” Lopez Lang said. “I think it’s going to be really exciting to see.”
CNN’s Andrew Freedman contributed reporting.
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