High in the atmosphere above the Arctic, something strange is happening: the polar vortex has broken down earlier than ever recorded, a phenomenon that can trigger a blast of cold weather in parts of the Northern Hemisphere. However, there’s also another unprecedented force at work in the form of a historically strong El Niño, which typically drives warmer global temperatures. It’s setting up an atmospheric battle for influence over our weather — and it’s not yet clear which will win. The polar vortex is a belt of strong winds high in the atmosphere that tightly hugs the Arctic’s frigid air, keeping it locked up around the North Pole. It forms every fall as the sun sets on the top of the world and the dark Arctic nights begin. Although it exists in the stratosphere, about 10 to 30 miles (16 km to 48 km) above the Earth’s surface, it can play a strong role in shaping the Northern Hemisphere’s winter weather patterns. For the past few weeks, the polar vortex has been weakening. Right now, the air in the stratosphere is warming dramatically in a phenomenon known as a “major sudden stratospheric warming” event, where the polar vortex’s winds reverse. In the days and weeks after this happens, Arctic air can spill south into the Northern Hemisphere, loading 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 happening on Nov. 28 in both 1968 and 2025. It’s not yet clear why this disruption is happening so early. It’s possible El Niño may have played a role — some research has linked it to a weaker polar vortex and more frequent major disruptions. “But we’re not sure yet,” said Simon Lee, an atmospheric scientist at the University of St Andrews. What’s certain is that its unprecedented nature makes it hard to understand exactly how the impacts will play out and where. “It’s happening so early in the season that basically our historic events don’t capture what’s actually happening,” Lopez Lang said. The first taste of winter Parts of the U.S. and Europe will get their first taste of winter this week, with a blitz of cold conditions that may have ties to the polar vortex disruption. A blast of Arctic air spilled out over North America and Europe Wednesday, which will last into the weekend — with peak cold on Thursday or Friday for most places. This will mean widespread frost, the first for much of the Eastern U.S. and Northwest Europe. This cold is not expected to be particularly extreme but will be a sharp break from the unusual warmth of summer and fall in places such as the U.S. East Coast and the U.K. In the U.S., nearly everywhere east of the Mississippi River will experience the coldest weather since spring, with most of the eastern half of the country enduring temperatures around 7 to 14 degrees Fahrenheit (-13 C to -10 C) below mid-November averages. Similar anomalous cold will also affect northern Europe. This cold snap will not linger long, however, with above average temperatures set to return in the eastern U.S. and other regions next week. This week may just be the “appetizer,” with the more impactful “main course” still to come, said Judah Cohen, an MIT climatologist. The effects of a disruption typically take a few weeks to filter down, and there’s an increased risk of colder weather to both eastern North America and northern Europe in late November or early December, he said. The El Niño factor Polar vortex disruptions don’t automatically translate to blockbuster cold, especially when they happen earlier in the season before the Arctic cold has had a chance to really build — and when there’s a super-sized El Niño to contend with. El Niño is the “big bully pushing the atmosphere in a certain direction,” Lopez Lang said. She thinks its impact will be “so overwhelming” that while we may see some cold air, it’s unlikely to be anything outside of what would be expected during a typical winter season. Amy Butler, a research physicist at NOAA’s Chemical Sciences Laboratory, echoes this. “The feature that stands out to me over the next month, is the higher chance of warm temperatures over the northern half of the U.S., likely related to El Niño,” she said. Some disagree. There’s an assumption that “El Niño is kind of this runaway freight train, and nothing’s going to get in the way of it,” MIT’s Cohen said. It is important, he added, but “whether there’s cold air or not will depend on the behavior of the polar vortex.” There’s the impact of global warming to consider, too, said Jason Furtado, an associate professor of meteorology at the University of Oklahoma. Winters are warmer on average than they were just a few decades ago. “That means everything is relative when we talk about any potential cold air outbreak,” he said. An atmospheric experiment It looks like the polar vortex will strengthen again quickly after this event, said NOAA’s Butler. “It might be that this disruption doesn’t have much staying power,” she said. But there may be further polar vortex disruptions to come. “I wouldn’t be surprised if we saw another one this winter,” Lopez Lang said. “And the next one might be the one that we actually have the impacts from.” This unique winter will give scientists the chance to see whether El Niño is taking charge of the weather or whether the polar vortex can still flex its considerable muscle. “The atmosphere is setting itself up to be an experiment,” said Lopez Lang. “I think is going to be really exciting to see.” CNN’s Andrew Freedman contributed reporting. By Laura Paddison, Brandon Miller, CNN
