Here’s What to Know About the Polar Vortex Collapse

You could be forgiven for not noticing that last month was the planet’s third warmest February on record. That’s because local temperatures plunged during the third week of February 2025, shattering records across the plains, the Gulf of Mexico, and the East Coast. Baker, Mont., saw a low of -22°F, its coldest day since 2009. Bismarck, N.D., fell to -39°F, six degrees from its all-time coldest day. The cause of the week-long deep freeze? A polar vortex collapse. Now, meteorologists are calling for another collapse in the middle of March, one that could plunge the U.S., Canada, and parts of Europe into a bitterly cold spell just days before the official arrival of spring. So what is a polar vortex collapse and why does it affect weather so dramatically?

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As the National Weather Service explains, the polar vortex is an area of low pressure and cold air that exists over both of Earth’s poles 10 to 30 miles above the surface. The term vortex is used to indicate that the air flows in a counterclockwise direction. Both polar vortexes are present year-round, but they weaken in the summer and strengthen in the winter, governed by rising and falling seasonal temperatures. South of the Arctic’s polar vortex is the jet stream, a river of west to east air that flows five to nine miles above ground, and helps keep the pole’s cold air confined to the Arctic. When the vortex weakens—which it does on occasion—the jet stream becomes wavy, bulging south and allowing Arctic air to flow down across North America and Eurasia, causing temperatures to plummet across the affected areas.

More dramatic than a weakened vortex is a collapsing vortex. That occurs when a layer of Arctic air 10 to 30 miles above the surface warms by 50°F or more over a period of just two days, a phenomenon known as a sudden stratospheric warming (SSW). The SSW more powerfully weakens the polar vortex, slowing the spin that keeps frigid air at home in the Arctic and allowing it to spill southward. An SSW led to the bitter, snowy conditions in February, and weather models predict that another one is already forming and could result in a collapse as early as next week and as late as early April. Whether climate change is playing a role in the twin collapses—with increasing global temperatures leading to rising stratospheric temperatures—is unclear. Meteorological records of stratospheric temperatures reach back only to the 1950s, making for a spotty dataset.

How long the coming collapse will last is uncertain, depending entirely on how strong and enduring the SSW is. The atmospheric warming may cause the vortex to become stretched or displaced off of its pole-centric position. But on occasion it can cause the vortex to split entirely in two. That, meteorologists warn, could lead to a cold spell that lasts weeks.

“The polar vortex has been particularly strong and stable the past few weeks. That has kept the coldest of Arctic air largely confined to the North Pole,” says Mike Bettes, meteorologist with the Weather Channel. “Longer range models indicate there may be a rapid weakening of the polar vortex beginning in mid-March. Because there is typically a lag in how the near-surface atmosphere responds to the polar vortex, this would mean unusually cold temperatures affecting parts of North America and Eurasia at the end of March and beginning of April.”

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