How A Weak La Niña Could Affect Winter Snowfall

A​ weak La Niña is expected to develop this winter and it could have some influence on snowfall over the U.S.

What is La Niña? La Niña is the periodic cooling of water in the eastern and central Pacific Ocean near the equator. When sea-surface temperatures are cooler than average by at least 0.9 degrees Fahrenheit (0.5 degrees Celsius), and the atmosphere has responded to that for at least three consecutive months, a La Niña is declared.

Spanish for "little girl", it's the oceanic opposite of El Niño, which was discovered in the 17th century by fishermen who first noted El Niño's warm water off the Pacific coast of South America.

It’s expected soon: According to NOAA’s Climate Prediction Center, La Niña is expected to develop and last through winter 2024-25.

As of the time this article was published, most computer model guidance suggested this La Niña probably will be weak.

Why it matters: While not the only influence, La Niña's cooling effect on the equatorial Pacific waters can affect weather patterns thousands of miles away, including near the U.S.

And that means it could affect snowfall, among other things, this winter.

So, let’s take a closer look at past weak La Niña winters to see if there are any clues as to how this winter's snowfall may look. Then we’ll finish with some important disclaimers.

The general overview: NOAA’s Climate Prediction Center examined snowfall during weaker (and stronger) La Niñas from 1950-2009 and found an interesting pattern.

Namely, weaker La Niñas generally produced above-average snowfall across much of the northern tier of the U.S., from the Cascades of the Northwest through the upper Midwest and New England.

Less snow than average typically occurs in the southern Rockies and parts of the Ohio Valley.

R​egional views: We also examined snowfall during 12 previous weak La Niña winter seasons since 1950 for several cities in each region, to see if a signal could be teased out of the data.

N​ortheast

T​he overall picture that emerged is a less snowy winter along the I-95 Northeast corridor, especially in the Mid-Atlantic states. For example two of the 12 weak La Niña winters were snowier than average in Washington, D.C.

H​owever, snowier winters were seen in both the eastern Great Lakes snowbelts - Buffalo and Syracuse, New York - as well as in northern New England.

Midwest

T​he north-south split was particularly sharp when examining the nation's mid-section.

Bismarck, North Dakota; Duluth, Minnesota; and Minneapolis-St. Paul each averaged at least 10 inches more snow during weak La Niña seasons than average.

West

W​e found much of the West, with a few exceptions, picked up more snow during a weak La Niña.

T​hat was the case in Alaska, the Cascades, Great Basin, northern Rockies and at least in parts of California's Sierra.

T​he exceptions were the southern Rockies as far north as Denver. Albuquerque, New Mexico, had a tendency for their least snowy winters during weak La Niñas.

South

Think of the numbers you see below as a decreased chance of snow, or fewer snow events in the South, rather than focusing on the exact figures, given the region's less snowfall compared to the rest of the country.

T​he overall takeaway is a lower chance of snow in a weak La Niña winter. It was a consistent signal we noticed from the Texas Panhandle to Virginia.

E​ven typically snowier Roanoke, Virginia, had a 36 percent reduction in their seasonal snowfall during weak La Niña winters.

The asterisks*: The values we calculated above were averages over 12 weak La Niña seasons. Averages can, and often do, mask significant season-to-season variability.

F​or example, while Philadelphia exhibited a decent less snowy signal when all 12 weak La Niña seasons were mathematically smushed together, those seasons ranged from almost 30 inches of snow in 2017-18 to as little as 0.3 inches in 2022-23.

The reason for that variability is the evolution of weather patterns over a winter season has many factors driving it, not just La Niña.

Furthermore, a weaker La Niña could have less influence on weather patterns compared to a stronger La Niña.

Another occasional winter pattern influencer can be sudden, sharp warming events high in the atmosphere known as sudden stratospheric warmings.

These disrupt and weaken the polar vortex, which can then set up blocking patterns that bring much colder air into the U.S. weeks later in winter, regardless of La Niña.

Finally, there’s climate change.

Winter is the fastest-warming season in much of the nation over the past several decades, according to a study from Climate Central. Cold outbreaks are shrinking in duration and aren't as cold. Parts of the Midwest and Northeast are seeing over two more weeks of warmer than average winter days now compared to 1970, Climate Central found.

All these factors make winter seasonal forecasts challenging, including in 2024-2025.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on X (formerly Twitter), Threads, Facebook and Bluesky.