Polar vortex may break down in early November, earliest in records back to 1958

What the forecast models show

Ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) have been converging on the same outcome over the past few days. On the midnight run of Monday, 26 October, 18 of the 50 scenarios the centre calculates each day projected a breakdown of the vortex within the following 15 days. Twelve hours later that number had climbed to 23, and by Tuesday, 27 October, it reached 43. By Thursday, 29 October, all 50 scenarios pointed the same way. The models now point to a reversal of the stratospheric winds between 4 and 10 November, which would amount to a sudden stratospheric warming.

26 Oct, midnight run18

26 Oct, 12 hours later23

27 Oct43

29 Oct50

26 Oct, midnight run

18 scenarios out of 50

26 Oct, 12 hours later

23 scenarios out of 50

27 Oct

43 scenarios out of 50

29 Oct

50 scenarios out of 50

Data from the article text

Timing and scale

The polar vortex is a band of strong westerly winds that sits roughly 12 to 50 kilometres above the Arctic and normally strengthens through the autumn. A Severe Weather Europe analysis says the stratospheric winds could reverse direction around 4 November. ECMWF runs show a sharp weakening of the westerlies during the first week of November, with some scenarios turning them fully easterly. ECMWF forecasts also point to stratospheric temperatures rising by as much as 22 degrees Celsius above normal at about 30 kilometres, and the vortex could split into centres above Siberia and North America. Forecast analysis puts the expected event about three weeks earlier than the previous record, and such an early warming has not been recorded in the data series that begins in 1958.

Possible effects on Europe

Forecasters say the first weather effects could appear in the second week of November, with some forecasts showing temperatures below seasonal averages across western, central and southern Europe around 8 November. MeteoNews expects the vortex to weaken two to three weeks earlier than last year and says a strong anticyclone could form over the North Sea, favouring the bise in Switzerland. Forecasts for London suggest freezing temperatures could arrive sooner than the January drop first expected. NASA forecasts show the wind circulation weakening, with wind strength falling from 26.9 mph on 31 October to 20.5 mph on 1 November and 9.3 mph on 3 November. Forecasters also warn that blocking high pressure over the North Atlantic and Scandinavia could bring prolonged cold, dry weather to northern Europe, while southern Europe would see milder, wetter conditions.

2026-10-31

26.9 mph

2026-11-01

20.5 mph

2026-11-03

9.3 mph

Data from the article text

Caution from researchers

Scientists stress that a weaker vortex does not automatically mean snow or hard frost. Bogdan Antonescu, a researcher in atmospheric physics, told Euronews that any disruption remains uncertain and that its effects would take weeks to reach the ground. He said the chances of cold in Europe in December or January have risen, but that this is not a forecast of a harder winter.

“It is not, in practice, a forecast saying that a harder winter is coming.”

Judah Cohen, a researcher at the Massachusetts Institute of Technology, took a stronger view in comments to Fox Weather.

“This will be, I think almost undoubtedly, the largest, earliest disruption of the polar vortex on record.”

Longer-range ECMWF forecasts suggest a possible new weakening of the vortex from January 2027, and El Niño, developing in the Pacific, is being factored into the outlook. An analysis of 34 stratospheric warming episodes found they were often followed by colder periods in northern and central Europe.