Polar Vortex Forecast Signals Unprecedented Early Disruption

Forecast models indicate that the polar vortex could experience an unusually early major disruption in November 2026, potentially setting a record and influencing winter weather across the United States. Climatologist Judah Cohen of the Massachusetts Institute of Technology said the event could develop nearly three weeks earlier than the earliest previously known major disruption, although its eventual effects on US temperatures remain uncertain.

According to Cohen, major polar vortex disruptions typically occur in January and February, with occasional events in December. Records show no November disruptions of comparable magnitude in the satellite era, while only two were documented before satellites became available, when observations were less reliable.

The European Centre for Medium-Range Weather Forecasts (ECMWF) reports that 86% of its forecast models predict the polar vortex will reverse direction by November 10. The center's records, which began in 1959, contain no previous major sudden stratospheric warming event occurring this early in the year.

Cohen described the historical significance of the forecast while cautioning that the models face an unusual prediction challenge.

"This level of polar vortex disruption is most common in January and February. Occasionally it has happened in December, though none so far this century." Cohen told Gizmodo in an email.

The polar vortex is a broad circulation of low pressure and cold air that rotates counterclockwise around the North Pole. Forming in the stratosphere each fall, it helps shape winter weather throughout the Northern Hemisphere by influencing how Arctic air moves toward lower latitudes.

When the vortex remains strong, its circulation helps confine cold air to the Arctic. If it weakens significantly, however, the circulation can stretch or become unstable, potentially allowing frigid air to move south and trigger Arctic outbreaks.

Large atmospheric waves traveling upward from the troposphere can weaken the vortex. When these waves disrupt the circulation enough to reverse its winds temporarily, temperatures in the stratosphere rise rapidly, producing a major sudden stratospheric warming (SSW) event.

The ECMWF forecast indicates that the vortex could stretch into an oval nearly three times as long as it is wide around November 1. That configuration could eventually favor the movement of Arctic air toward the United States, but a disruption does not guarantee an immediate cold spell.

Cohen warned that atmospheric changes in the stratosphere take time to affect weather closer to the ground. Although experts commonly estimate a delay of about two weeks, the impacts can take longer to materialize.

"I wouldn't expect to see the impacts until sometime in December," Cohen said.

The unusually early forecast is linked to strong Ural/Scandinavian blocking, according to Cohen. A high-pressure system positioned over northwestern Russia and Scandinavia is directing large atmospheric waves upward into the stratosphere, increasing the likelihood of a weakened polar vortex.

Because forecast models have not previously encountered an event this early, Cohen said their ability to predict its development may be limited.

"The models have never seen an event as early as this, so they're going to struggle with it," Cohen said.

The potential disruption could also complicate expectations for the US winter, even as an exceptionally strong El Niño is forecast to influence seasonal conditions. El Niño often favors milder winters across parts of the country, but the polar vortex can produce a different outcome.

Cohen cited the winter of 2009 and 2010 as an example of this interaction. Despite El Niño favoring milder conditions, a very weak polar vortex contributed to a colder winter.

He said the limits of El Niño's influence over cold air outbreaks remain uncertain.

"Is there a point where the El Niño is so strong that it can deflect any cold thrown at us by the polar vortex? I don't know, and I argue that no one else does either," Cohen said.