A severe winter storm that brought freezing rain, sleet and snow to a large part of the U.S. was intensified by the polar vortex and warm ocean.
A severe winter storm that brought crippling freezing rain, sleet and snow to a large part of the U.S. in late January 2026 left a mess in states from New Mexico to New England. Hundreds of thousands of people lost power across the South as ice pulled down tree branches and power lines, more than a foot of snow fell in parts of the Midwest and Northeast, and many states faced bitter cold that was expected to linger for days.
The sudden blast may have come as a shock to many Americans after a mostly mild start to winter, but that warmth may have partly contributed to the ferocity of the storm.
As atmospheric and climate scientists, we conduct research that aims to improve understanding of extreme weather, including what makes it more or less likely to occur and how climate change might or might not play a role.
To understand what Americans are experiencing with this winter blast, we need to look more than 20 miles above the surface of Earth, to the stratospheric polar vortex.
What creates a severe winter storm like this?
Multiple weather factors have to come together to produce such a large and severe storm.
Winter storms typically develop where there are sharp temperature contrasts near the surface and a southward dip in the jet stream, the narrow band of fast-moving air that steers weather systems. If there is a substantial source of moisture, the storms can produce heavy rain or snow.
In late January, a strong Arctic air mass from the north was creating the temperature contrast with warmer air from the south. Multiple disturbances within the jet stream were acting together to create favorable conditions for precipitation, and the storm system was able to pull moisture from the very warm Gulf of Mexico.
Where does the polar vortex come in?
The fastest winds of the jet stream occur just below the top of the troposphere, which is the lowest level of the atmosphere and ends about seven miles above Earth’s surface. Weather systems are capped at the top of the troposphere, because the atmosphere above it becomes very stable.
