Final polar vortex collapse of the season begins

The final polar vortex collapse of the 2024–25 season has begun, according to an analysis by Andrej Flis, published on March 5, 2025, by Severe Weather Europe (SWE).

A strong SSW event has begun and will trigger the rapid collapse of the stratospheric polar vortex. As it progresses, a high-pressure system developing over Greenland and eastern Canada will bring late-season cold to much of the United States.

The high-pressure system has expanded significantly, exerting pressure on the polar vortex. A strong warming wave has also developed on the outer edge of the vortex, marking the onset of the SSW event that will lead to its full collapse.

As the high-pressure system strengthens, it will begin to influence the lower levels of the vortex, triggering a major shift in the stratosphere. Depending on how pressure anomalies in the lower levels interact, this event could significantly impact weather patterns across the United States and the Northern Hemisphere.

The polar vortex wind forecast from March 5 to 20 indicates negative values, meaning that winds have reversed from westerly to easterly.

The forecast places the wind reversal near the historic minimum threshold, indicating that the upcoming SSW event will be one of the strongest recorded for this time of year. A strong wind reversal is the primary criterion for classifying an event as a major SSW event.

The temperature forecast during the event shows a sharp increase due to a strong warming wave in the stratosphere. There is no indication of a cooldown after the warming, suggesting that the vortex will not recover until the 2025–2026 winter season.

The vortex is expected to split as the stratospheric high-pressure system dominates the polar regions over the next 10 days.

An SSW event typically results in high-pressure anomalies from the stratosphere reaching the surface, disrupting the jet stream. This disruption allows cold air from the polar regions to move into the United States and other mid-latitude regions.

Since the SSW event has just begun, it is still too early to provide precise forecasts. Currently, it is expected to bring cold air from the polar regions into the United States. A cooler zone is also forecast over northern and northwestern Europe due to high-pressure blocking over Greenland and eastern Canada.

Most weather models currently predict a cold air mass spreading across the central, eastern, and northeastern United States. However, the forecasts are still in the early stages and may change as the event unfolds.

References:

¹ The Polar Vortex collapse event has begun, with the first Weather impacts now visible in the Forecast over North America – SWE – March 5, 2025