La Niña has arrived. Here’s what this means for the US

CNN
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La Niña has finally emerged after months of anticipation, but there’s a catch. The climate pattern — which typically has an outsized impact on winter weather in the U.S. — is rather weak and may not last long.

But that won’t completely eliminate its effect. And despite its late arrival, it has already played a significant role in this winter’s weather.

Forecasters watch La Niña and its counterpart, El Niño, closely because they influence global weather in ways that are largely consistent and predictable well in advance — especially when the patterns are strong.

Last winter was the warmest on record in the US and was dominated by a very strong “super” El Niño. This winter is different: La Niña is not only much weaker than last year’s strong El Niño, it is also coming really late to the party. Both exert their greatest influence on the weather in the winter months, and this La Niña has already lost a lot of time, according to Emily Becker, a research professor at the University of Miami.

“It’s really starting to happen right at the time when it normally peaks (in strength) and starts to wane,” explained Becker, who is also a lead author of NOAA’s La Niña/El Niño blog.

But that doesn’t mean its impact on winter weather in the U.S. is insignificant.

The phenomenon is characterized by water that is cooler than average Temperatures in the equatorial Pacific, along with corresponding changes in upper atmosphere patterns – and these changes influence weather worldwide.

In the fall, the atmosphere started to look La Niña-like, but ocean temperatures didn’t really look like La Niña until the end of the year, Becker explained.

Despite the timing and its weakened state, La Niña’s atmospheric influence was already evident this winter.

California is the most obvious example. Winter in Northern California is typically wetter during La Niña, while the southern half of the state is drier than normal. These extremes play a big role: Northern California has had plenty of rain, while Southern California is so tinder dry that thousands of acres went up in flames this week.

La Niña also typically brings more rainfall to the Midwest. Several major cities in the Midwest — including St. Louis, Indianapolis and Cincinnati — are experiencing one of their wettest starts to winter yet, according to data from the Southeast Regional Climate Center.

But there are also exceptions that prove that La Niña is not the only factor this season.

The South and parts of the central U.S. are typically drier and warmer than normal during a La Niña winter, but that has been far from the case, at least in the last few weeks. The eastern two-thirds of the country has experienced periods of brutally cold Arctic air since December, and winter storms have brought disruptive weather every week since the start of the year.

According to the Climate Prediction Center, the weak La Niña is expected to last until April before returning to so-called neutral – not La Niña or El Niño – conditions.

Trends for the remainder of the winter and into early spring still show the influence of La Niña, but there is no guarantee that the season will play out exactly like a typical La Niña.

“If La Niña were stronger, I would be more confident … that the rest of the winter would be very similar to the expected impacts of La Niña,” Becker explained, pointing out that the weaker La Niña leaves room for other atmospheric factors to exert influence .

Still, much of the southern region of the U.S. and the East is expected to experience warmer than normal temperatures from January to March, according to the CPC. Cooler than normal conditions are expected for some northwestern states, which is also typical of La Niña.

Weather conditions are expected to continue into March in the Northwest and Midwest, as well as parts of the Northeast. More precipitation combined with colder weather could be a recipe for bouts of snow into early spring. Much of the southern U.S. is expected to become drier than normal, but parts of the Mississippi Valley and the Southeast could be an exception.

CPC long-range forecasters first raised the possibility of a shift to La Niña in February 2024, when El Niño was still very strong. At the time, experts expected La Niña to arrive in the summer or fall and increase hurricane activity in the Atlantic.

El Niño finally lost control of global weather in June, but La Niña’s arrival was repeatedly delayed, resulting in an extended period of neutral conditions throughout the summer and fall. It turns out that hurricane season didn’t need La Niña to have devastating effects anyway.

Becker said the delay is likely related to global ocean temperatures, which have been well above average for more than a year. Global air temperatures continued to be extreme in 2024, which is likely to be the first year on record that a critical warming limit will be exceeded.

It proved difficult for the equatorial Pacific to cool into a La Niña phase because the surrounding oceans and atmosphere retained so much extraordinary heat.