In late January 2026, a severe winter storm will sweep across central and eastern U.S. with freezing rain and snow. Forecasters warned that the bitter cold would last for several days and cause dangerous travel conditions.
This sudden storm may have surprised many Americans, especially after an essentially mild winter. However, this warmth could be contributing to its ferocity.
We are atmospheric and climate researchers who conduct research to better understand extreme weather. This includes what causes it to be more likely or less probable to happen, and whether climate change plays a part or not.
We need to take a look at the stratospheric vortex, which is located more than 20 miles up in the air.
The freezing line is shown in white on a forecast of Jan. 26 2026. It reaches as far south as Texas. The dark band is the stratospheric vortex, while the light band has arrows to indicate the jetstream. About 3.5 miles is the height of the jet stream, which is a standard for tracking storms. Polar vortex hovers at approximately 20 miles.
Mathew B. Barlow, CC BY
What causes a winter storm of this severity?
For a storm to be so large and violent, multiple weather conditions must come together.
Winter storms are usually formed when there is a sharp contrast in temperature near the surface, and where the jetstream (the narrow band of air moving fast) dips southward. Storms that are accompanied by a large amount of moisture can cause heavy snow or rain.
Late January saw a temperature contrast between arctic air masses from the north and warmer air coming from the south. The jet stream was affected by multiple disturbances, which created favorable conditions for rain. This storm system also pulled moisture from the warm Gulf of Mexico.
On Jan. 24, 2026 the National Weather Service (NWS) issued severe storm (pink), ice storm (dark violet) warnings in several states, and extreme cold (darkblue) warnings for large areas of the U.S.
National Weather Service
What is the Polar Vortex?
Jet stream winds are strongest just beneath the surface of the troposphere. The troposphere is the lowest layer of atmosphere, and it ends approximately seven miles above the Earth’s surface. The top of troposphere is where weather systems end because it’s a very stable atmosphere.
It is the layer above, ranging from seven to thirty miles. The stratosphere is high above the weather system, but it still has the ability to interact with the systems through the atmospheric waves which move up and downward in the atmosphere. The waves that move up and down in the atmosphere are very similar to those waves which cause the jetstream to bend southward. However, they do not travel horizontally.
The chart below shows the temperature change in lower atmosphere layers between tropospheres and stratospheres. On the chart, miles are to the right and kilometers to the left.
NOAA
When an area of Arctic cold air travels far enough south to affect the United States, it is called a “polar vortex”. This term is used to describe air moving around the pole. However, it could refer to either the troposphere or the stratosphere.
A belt of air that is moving fast around the North Pole in Northern Hemisphere, known as a stratospheric vortex. This is a jetstream that’s higher than the usual one, usually more wavy, but closer to the North Pole.
The polar vortex, which is a stratospheric storm that stretches southward from the United States. This creates the perfect conditions for waves to move up and down, connecting the stratosphere at the surface with the severe winter weather.
Left, a stretched stratospheric vortex bounces upward waves down to affect the surface weather and jet stream.
Mathew Barrlow and Judah Cohen CC BY
Forecasts for January’s storm indicated that the jetstream and stratospheric vortex were close to overlapping, which would have created ideal conditions for snow and cold.
Energy is the main cause of the biggest jet stream swings. If the conditions are right, this energy could bounce back off the polar Vortex and into the troposphere. This would increase the severity of winter weather across North America.
What happened in January 2026?
Why do we continue to have severe winter weather if the climate is changing?
The Earth’s surface is undoubtedly warming, as humans emit greenhouse gases that trap heat and the amount of snow on Earth has been decreasing. It does not, however, mean that severe weather conditions will never occur again.
Some studies suggest that, even in an environment where temperatures are rising, the severity of cold weather events may not change.
Climate change is believed to have a direct impact on the Arctic. This rapid warming has caused the stratospheric vortex to become more unstable.
Polar vortex, a powerful band of wind in the stratosphere that normally circles the North Pole. It can break up when it becomes weaker. This upheaval can be mirrored by the polar jetstream, which becomes weaker or waver. Cold air can be pushed to the south in certain locations.
NOAA
A warmer ocean also leads to increased evaporation. And because warmer air can contain more moisture, this means that more moisture will be available for storms. Storms are also fueled by the condensation of moisture into snow or rain. The warming of the earth can reduce storm strength by decreasing temperature contrasts.
It is difficult to predict the change in average storm intensity due to these opposing forces. Extreme events may not change the same as normal events. Overall, the intensity of winter storms is increasing.
The warmer the environment, the more likely it is that rain and sleet will fall instead of snow.
Many questions remain.
There are still many questions to be answered, even though scientists are improving their ability to predict severe weather and how to respond.
Many of the research and data in this field are based on the work of federal employees. This includes government laboratories like the National Center for Atmospheric Research (NCAR), which is being targeted for cuts by the Trump Administration. They help to develop models, measurement instruments and data on which scientists and forecasters rely.
