La Niña has a significant impact on winter weather in the United States, but its effects vary widely by region.
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While the polar vortex has been the talk of the town in recent weeks, federal forecasters say its old friend La Niña remains the primary factor shaping America’s winter weather.
Federal scientists at the National Oceanic and Atmospheric Administration’s Climate Prediction Center (CPC) acknowledged that the La Niña weather pattern that began in October is expected to continue shaping U.S. weather through the winter of 2025-2026, according to a monthly update released Thursday, Dec. 11. Meteorologically, December, January, and February are considered winter.
La Niña and the polar vortex are already dancing the Arctic shuffle, with the polar vortex determining how far south the cold air comes, and La Niña often channeling that air in the direction it wants.
As of mid-December, a portion of the polar vortex is poised to release unspeakably cold air into the central and eastern United States.
The vortex will then recede and a more typical La Niña-like pattern could persist through at least late December and into January, forecasters said.
What is La Niña?
La Niña is part of a natural climate cycle officially known as El Niño Southern Oscillation, which scientists refer to as ENSO. This cycle moves back and forth between warm and cold ocean water in areas along the equator of the tropical Pacific Ocean. La Niña is characterized by lower than average seawater levels in the region.
This is one of the main factors that determines the weather in the United States, especially in late fall, winter, and early spring. This is the opposite of the better-known El Niño, which occurs when Pacific water temperatures are at least 0.9 degrees warmer than average for three months.
The intermediate stage is known as ENSO-Neutral, where neither La Niña nor El Niño exists.
A map showing how La Niña generally affects winter weather, snow, and cold.
Will La Niña continue to impact U.S. weather for the remainder of winter 2025-2026?
“CPC’s latest seasonal outlook shows a clear impact of La Niña on precipitation anomalies from at least February through April,” CPC climate scientist Michel Leroux said in a Dec. 10 email to USA TODAY.
When La Niña began in October, federal weather forecasters expected it to last into February.
“La Niña conditions are consistent with drier conditions in the southern part of the state and wetter conditions in the northern part,” she said.
As for snow, the Northwest, northern Rocky Mountains, Great Lakes, and interior Northeast will likely continue to experience extreme snowfall.
“A more normal La Niña pattern”
As the polar vortex recedes later this month, U.S. winter weather will become more dependent on La Niña, AccuWeather’s Paul Pastelok told USA TODAY this week.
“This should facilitate a return to a more normal La Niña pattern,” he said.
When will La Niña end?
“At this time, we support a transition to ENSO neutrality during the January-March 2026 season,” Rollou said.
Additionally, “Even after equatorial Pacific sea surface temperatures transition to ENSO-neutral values, La Niña events may remain to some extent into early spring 2026 in the Northern Hemisphere,” the CPC report said.
Is El Niño next?
“It’s too early to say at this point,” Rollou said. “Although the likelihood of an El Niño occurring in mid-late 2026 is increasing, the probability remains less than 50%. This reflects the increased uncertainty typically seen when these forecasts pass the ‘spring predictability wall.’”
The barrier comes when weather models have difficulty making accurate seasonal predictions.
If El Niño develops, it could act as a dampener on hurricane activity in the Atlantic basin next year.
(This article has been updated to add new information)
