Why has this winter been so cold in the U.S. East and warm in the country’s West?

Why was this winter so cold?

By Andrea Thompson edited by Jeanna Bryner & Clara Moskowitz

The latest bout of extremely cold weather that has plagued the eastern United States for weeks brought wind chills in the teens and 20 degrees Fahrenheit (minus 20 degrees to minus 30 degrees Celsius) across the northeastern United States over the weekend. Meanwhile, in the West, winter brought record-breaking warmth that is better suited to spring and even summer. “I’m sitting here in a T-shirt in early February, a mile up in Colorado,” says climate scientist Daniel Swain of the California Water Resources Institute.

This strong disparity is the product of a persistent atmospheric pattern. This trend, however, is about to break and the weather conditions in both halves of the country are about to change.

To explain what’s going on, let’s review a favorite winter bugaboo: the polar vortex. The vortex is like a circular river of wind that brings together the coldest air in the Arctic. As the vortex weakens, this tight circle becomes more wavy, much like a slow-moving river that tends to meander through the landscape, Swain explains.

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Where the vortex bends south, cold air follows. And if it curves south in one place, it must curve north in adjacent areas. In this case, the northward turn is occurring over the western United States, where it has brought warmer air with it.

These turns tend to be set in ways that reinforce the background conditions related to Earth’s geography, Swain explains. In the case of the United States, the location of the Rockies, along with the boundary between the Pacific Ocean and land, means that on average, a weak ridge (a northward bend of the jet stream) forms over the west and a weak trough (a southward bend) is established over the east. The current dichotomy “is an amplification of this background pattern – a dramatic pattern,” says Swain.

Rapid warming in the Arctic could make this weakening of the polar vortex more common, but researchers aren’t yet sure. “To the extent that this is happening, it hasn’t been enough to overcome the fact that this source of frigid air is no longer as frigid as it used to be,” Swain says.

This effect relates to the current situation. For the period from December 2025 to January 2026, no region in the contiguous United States experienced record cold. But 21% of the country experienced the hottest period since 1940, according to climatologist Brian Brettschneider.

And as winters get warmer overall, these bitter cold spells become more disruptive because they are so unusual. People are less accustomed to frost and businesses cannot make contingency plans. “For someone 25 or 30, they might have had the coldest week of their life,” Swain says, while for those in the West, “it was the warmest winter, regardless of age.”

Although the consequences of the cold have been widespread and severe – with travel disruptions, power outages and many deaths – the warm Western winter will also have detrimental consequences. However, its consequences will be delayed, with a risk of drought, water shortages and an increased risk of forest fires in the months to come.

The next weather change is likely to come down to a subtle atmospheric shift. Understanding the details would require a dedicated study to analyze all the influences, Swain says, but it could lead to a change in where storms occur in the tropical Pacific, which can topple objects in the atmosphere like dominoes. Whatever the cause, temperatures will rise to more seasonal levels in the eastern United States, and cooler, wetter weather will set in in the west. Any rain or snow will be welcome, Swain said, but probably won’t be enough to erase the current deficit.

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