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The polar vortex has reversed direction in the earliest major sudden stratospheric warming on record, raising the possibility of cold weather in North America, though experts say impacts remain uncertain.
The polar vortex high above the Arctic has reversed direction, marking the earliest major sudden stratospheric warming on record. The spiralling winds usually blow in a westerly direction, keeping cold air locked above the North Pole, but observations have shown a switch to easterly winds.
The polar vortex is a normal feature of the climate in the months around winter. As the North Pole tilts away from the sun, temperatures above the Arctic drop and strong westerly winds form in the stratosphere, roughly 10 to 30 miles above Earth's surface. A sudden stratospheric warming occurs when a rapid temperature rise causes the vortex's winds to weaken and potentially reverse into easterly winds.
The previous earliest SSW on record happened on 28 November in 1968 and 2025, according to CNN. The BBC reported the previous earliest SSW on record happened on 28 November in both 1969 and 2025. Because the sources disagree on the year, the earlier year is not included here.
Disruptions to the polar vortex can increase the possibility of cold weather, ice and snow in many regions, including North America. The effects typically take a few weeks to filter down through the atmosphere, altering the position of the jet stream which drives weather on the ground.
Judah Cohen, a climatologist at the Massachusetts Institute of Technology, told AFP that the early breakdown "really increases the chance of cold air outbreaks across the latitudes where most of the densely populated population centers are across the Northern Hemisphere, US, Europe and East Asia."
However, experts stress that an SSW does not automatically lead to cold or snowy weather. The Met Office, the UK's national weather and climate service, stresses that what is happening with the polar vortex can nudge odds in that direction, but it is not a switch that turns cold weather on and off.
Parts of the US 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, with peak cold on Thursday or Friday for most places. In the US, 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 below mid-November averages. This cold snap is not expected to linger long, with above average temperatures set to return in the eastern US next week.
The world is heading towards the expected peak of the strongest El Niño on record. El Niño is a natural weather pattern that develops in the Pacific Ocean and the atmosphere above it. Some research has linked it to a weaker polar vortex and more frequent major disruptions, but experts are not sure if it played a role in this event.
There is disagreement over how much influence El Niño will have. Andrea Lopez Lang, a meteorologist at the University of Wisconsin-Madison, thinks its impact will be "so overwhelming" that while some cold air may appear, it is 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, said the higher chance of warm temperatures over the northern half of the US is likely related to El Niño. Judah Cohen said El Niño is important but "whether there's cold air or not will depend on the behavior of the polar vortex."
This is the earliest stratospheric vortex disruption ever observed, according to European Centre for Medium-Range Weather Forecast principal scientists Tim Stockdale and Frederic Vitart. The French meteorological agency Meteo-France called it "an unprecedented event." Because it is happening so early in the season, historic events do not capture what is actually happening, making impacts especially uncertain. Scientists say there may be further polar vortex disruptions this winter, and the next one might be the one that brings actual impacts.
Sources
This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.
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