Impacts We Can Expect From Emerging La Niña

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A weak La Niña is expected to develop and that could have some influence on both winter temperatures and precipitation, including 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, La Niña is declared.

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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 this winter: According to NOAA’s Climate Prediction Center, La Niña is expected to develop this fall and last into 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 the distribution of temperatures and precipitation, including snowfall, 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 may look. Then we’ll discuss the key caveats.

Cold: We looked at 12 past weak La Niña winters - December through February - since 1950 to see if we could identify any general patterns.

The map below shows the December-February temperature departures from average, from all 12 taken together.

A general picture emerges. Colder than average from the Northwest into the northern Rockies and northern Plains, but warmer than average from the Gulf Coast into much of the East.

But when looking at each individual weak La Niña winter, there are variations on that theme. They range from the more widespread cold in the 1980s and 2000-2001, to the extreme, widespread warmth of 2005-2006, as the postage stamp maps below show.

This general picture can vary by month and area of the country.

In their initial outlook, Vice President of Meteorology at Atmospheric G2 Todd Crawford noted the eastern U.S. tends to be colder than usual early in winter (December) during weaker La Niñas, rather than late (February).

Snow: 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 high country of the Desert Southwest, as well as in parts of the Ohio Valley.

Precipitation: The signal of weak La Niña winter precipitation, combined rain and snow, is less distinct.

Smushing those 12 previous weak La Niñas together yields a generally drier winter near the Gulf Coast and Florida, and, somewhat surprisingly, along much of the West Coast. Typically, a stronger La Niña is wetter in winter in the Pacific Northwest.

Some patchy wetter winter spots stretch from the Mississippi Valley into the Ohio Valley and Great Lakes.

As we saw with temperatures, there’s also a wide variety of outcomes when we examined each individual La Niña winter's precipitation. Some were quite wet along the West Coast, and some were even wet in parts of the Southeast.

What happened last time: The most recent weak La Niña ended in late winter 2023. It largely persisted and followed two moderate-strength La Niñas starting in summer 2020, and was the first so-called "triple dip" La Niña in 22 years.

That winter was the among the warmest on record for many areas from Texas to the Midwest and East. It remains the warmest winter in 129 years in both Massachusetts and Rhode Island, according to NOAA.

It was also the wettest winter on record in some areas, from California’s Sierra to the upper Midwest. Wisconsin had its wettest winter dating to 1895.

The asterisks*: You’re probably wondering why there was so much variability among the 12 weak La Niña winters' temperatures and precipitation.

Just as you can’t point to one thing that’s driving the economy, the same is true of weather patterns.

First, as mentioned earlier, NOAA forecasters expect a weaker La Niña this winter. That means it could have a weaker 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.

Based in part on computer model forecasts and this expected weak La Niña, the chances of such a polar vortex disruption appear lower this winter, according to AG2’s Todd Crawford.

Finally, there’s the elephant in the room: 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 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.