Even as the planet warms, parts of the United States can still be hit with brutally cold winter weather—and scientists now have a clearer idea of why.
A team of researchers has identified two distinct patterns within the polar vortex, a swirling mass of frigid air located high in the stratosphere. These patterns influence where the coldest Arctic air ends up. One pattern tends to send freezing temperatures into the Northwestern U.S., while the other pushes cold air toward the Central and Eastern regions.
Arctic Cold in a Warming World
Even though winters across the United States are gradually becoming warmer overall, intense cold spells still strike large portions of the country with surprising intensity. A recent study provides new insight into this apparent contradiction. The explanation may be found more than 10 miles above the ground, in the evolving behavior of the stratosphere.
The research was conducted by an international group of scientists. Published in Science Advances, their work highlights how two distinct patterns within the stratospheric polar vortex—a band of extremely cold air that flows high above the Arctic—can lead to severe cold outbreaks in different regions of the United States.
“The public often hears about the ‘polar vortex’ when winter turns severe, but we wanted to dig deeper and understand how variations within this vortex affect where and when extreme cold hits,” said the researchers.
Vortex Variations and Regional Impact
The team identified two distinct variations of the polar vortex, both linked to what scientists call a “stretched” vortex—a distorted and displaced circulation pattern that leads to unusual weather on the ground.
- One variation pushes the vortex toward western Canada, setting the stage for intense cold in the Northwestern U.S.
- The other nudges the vortex toward the North Atlantic, unleashing frigid air across the Central and Eastern U.S.
Both versions are associated with changes in how atmospheric waves bounce around the globe—essentially altering the jet stream and dragging Arctic air far southward.
Why the Northwest Is Getting Colder
Perhaps most striking is the discovery that since 2015, much of the northwestern U.S. has been getting colder in winter, contrary to broader warming trends. The researchers tie this shift to the increased frequency of the westward-focused vortex pattern, which also coincides with stronger negative phases of the El Niño/Southern Oscillation (ENSO)—a key global climate driver.
“Climate change doesn’t just mean warming everywhere all the time. It also means more complex and sometimes counterintuitive shifts in where extreme weather shows up,” explained the researchers.
Forecasting the Unexpected
These findings help explain recent cold waves in places like Montana, the Plains, and even Texas, as in February 2021 (which was very costly in terms of deaths and insured losses), while other regions may experience milder winters. Understanding the stratosphere’s fingerprints on weather patterns could improve long-range forecasting, allowing cities, power grids, and agriculture to better prepare for winter extremes, even as the climate warms overall.
Notes
- The research was conducted by an international group of scientists.
- Prof. Chaim Garfinkel (Hebrew University)
- Dr. Laurie Agel and Prof. Mathew Barlow (University of Massachusetts)
- Prof. Judah Cohen (MIT and Atmospheric and Environmental Research AER)
- Karl Pfeiffer (Atmospheric and Environmental Research Hampton)
- Prof. Jennifer Francis (Woodwell Climate Research Center)
- Prof. Marlene Kretchmer (University of Leipzig)
Reference: “Cold-air outbreaks in the continental US: Connections with stratospheric variations” by Laurie Agel, Judah Cohen, Mathew Barlow, Karl Pfeiffer, Jennifer Francis, Chaim I. Garfinkel and Marlene Kretchmer, 11 July 2025, Science Advances.
DOI: 10.1126/sciadv.adq9557
The work was funded by a US NSF-BSF grant by Chaim Garfinkel of HUJI and Judah Cohen of AER&MIT.
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1 Comment
“Climate change doesn’t just mean warming everywhere all the time. It also means more complex and sometimes counterintuitive shifts in where extreme weather shows up,”
That sounds like an attempt to save the paradigm through a violation of Occam’s Razor. Perhaps one should consider an alternative interpretation: The noted changes are indications of a transition to a cooler climate. It might even be right. Stranger things have happened.