A La Niña winter is coming. Here’s what that could mean for the US

CNN

By Mary Gilbert, CNN Meteorologist

(CNN) — Fall is in full swing, but it’s not too soon to look ahead to winter, especially one that could feel considerably different than last year’s dominated by El Niño.

A weak La Niña is expected to develop ahead of the season and influence temperatures, precipitation, and by extension, even snow across the United States.

La Niña is a natural climate pattern that influences global weather marked by cooler than average ocean temperatures in the equatorial Pacific. The effects on weather are most pronounced during the winter months in the Northern Hemisphere and have a much weaker influence in the summer.

Last winter was the warmest on record for the Lower 48 because it was dominated by La Niña’s counterpart El Niño in a world also warming due to fossil fuel pollution.

The prolonged warmth prevented many heavy snow events in the Northeast and Midwest and created a winter snow drought measured in feet of missing snow.

La Niña isn’t here yet, but has a 60% chance of emerging through November, according to the Climate Prediction Center. Once it arrives, it’ll stick around all winter and likely persist into at least early spring of next year.

La Niña or El Niño are never the only factors influencing weather in a given season or location, but emphasis is placed on them because they typically have an outsized effect on winter weather in the US — especially when they are strong.

While it’s still unclear just how strong La Niña will get, current forecasts favor a weaker one.

The strength of La Niña matters — the stronger it is the more of a “consistent” impact it can have on weather, according to Emily Becker, an atmospheric scientist at the University of Miami.

“A weaker event makes it more likely that other weather and climate phenomena could play the role of spoiler,” Becker wrote in NOAA’s latest La Niña/El Niño blog.

Earlier forecasts from the Climate Prediction Center show many of the hallmarks of typical La Niña winters. That outlook could be change when the center releases its latest forecast on Thursday based on trends toward a weaker La Niña.

What could this winter look like?

No two La Niña winters are the same, but many have temperature and precipitation trends in common.

This is due to the behavior of the jet stream — essentially a river of air that storms flow through — which often shifts north during a La Niña winter. This typically shifts stormy weather out of the South and into parts of the northern US.

That’s almost exactly what the Climate Prediction Center’s latest winter forecast shows for December through February.

The entire northern tier of the US is expected to end up wetter than normal this winter, especially the Pacific Northwest, Midwest and parts of the interior Northeast. Wet weather will be crucial to combat ongoing dryness and drought in the Midwest.

It’s a complete flip from last winter’s pattern, which favored a wetter South and a drier North.

More precipitation than normal doesn’t guarantee there will be more snow. Temperatures still have to be chilly enough both above and at the surface for snow to fall and stick to the ground.

Weak La Niña events tend to allow for more snow in the Northeast, while snow is more limited during stronger La Niñas because warmer temperatures often creep farther up the East Coast.

If this year’s La Niña ends up rather weak, this outlook could shift. Still, the latest winter temperature forecasts from the center aren’t ideal for snow lovers in the Northeast.

The season is expected to be warmer than normal across almost the entire southern half of the US and much of the East. This could mean some winter storms in parts of the East end up wetter, rather than snowier. But with drier and warmer than normal conditions expected across the South, drought conditions could worsen throughout the season.

Parts of the Midwest, Plains and Rockies could end up with temperatures closer to normal this winter while cooler than normal conditions are expected from the Pacific Northwest to parts of the Dakotas.

The combination of wetter and cooler than normal conditions could potentially mean more snow for the Pacific Northwest, an area where a significant snowpack is crucial to tourism in the winter and the water supply for the warmer months.

Northern California is typically wetter during a La Niña winter, but the Climate Prediction Center’s forecast keeps the region near normal this season. La Niña had a hand in the extremely wet winter much of the state endured from December 2022 to February 2023 and during the wet winter before that.

Southern California is expected to be drier and warmer than average – typical for La Niña. It’s crucial the region gets a period of soaking rain in the next few months; wet weather is needed to shut down wildfire season. Without enough rain, fires could continue to burn through the overabundance of fire fuels like grasses or brush available this year.

The-CNN-Wire
™ & © 2024 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.