At a Glance

A strong El Niño is expected to remain in place through spring.Past strong El Niño winters were different in several aspects from what we saw last winter.That could include a cooler, wetter South and a snowier Mid-Atlantic. However, El Niño is not the only driver of weather patterns.

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A​ stronger El Niño is likely to be in place through spring, and that could mean big changes in snow, rain and temperatures compared to last winter in the U.S.

First, w​hat is El Niño and how strong is it? It’s a periodic warming of the equatorial eastern and central Pacific Ocean. This year’s El Niño first developed in June, and is the first in more than four years.

S​ince the end of August, its warm temperature anomalies have pushed above the threshold of a strong El Niño, at least 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, warmer than average.

Sea surface temperature departures from average (in degrees Celsius) during the last week of Oct. 2023. The El Niño is highlighted by the red arrows.

(NOAA/PSL)

W​hy does this strip of warm ocean water matter? El Niño and its cool counterpart La Niña can affect weather patterns thousands of miles away in the United States and around the world. Since most El Niños peak in late fall or winter, they can have their strongest influence in the colder months of the year.

In general, t​he classic El Niño winter tends to be wetter than average through much of the southern U.S., from parts of California to the Carolinas, due in part to a stronger, more southern jet stream track.

A​cross much of the northern U.S., a stronger El Niño tends to produce a warmer winter.

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Typical impacts during a stronger El Niño from December through February in North America.

(NOAA)

How could snowfall be different this season? Last season was a clear cut case of snow haves- and have-nots. Namely, much of the West into the Northern Plains and upper Midwest was snowier than average. However, much of the Northeast was markedly less snowy than usual.

2022-2023 season snowfall departure from average through April 5, 2023. While much of the West into the Upper Midwest was snowier than average, much of the Northeast was much less snowy last season.

(Greg Carbin (NOAA/NWS/WPC))

T​he two main changes in snowfall we may see this season due in part to this stronger El Niño are:

-​ Less snow: Pacific Northwest, northern Rockies and upper Midwest.

-​ More snow: Parts of the mid-Atlantic states.

Snowfall departures from average during moderate to strong El Niño January-March periods. Areas in brown typically have seen less snow, while those in blue have seen more snow.

(NOAA/Climate.gov)

A​s you can see, that's a pretty broad swath of the northern tier of states that may be less snowy this winter.

P​articularly interesting is the potential for a snowier mid-Atlantic region. Last season, Philadelphia, Baltimore and Washington, D.C. each failed to scrape up an inch of total snowfall. One of the more recent stronger El Niños happened in 2009-10, which included the in early February.

(​MORE DETAILS: How El Niño Impacts Seasonal Snowfall)

W​here could it be much wetter or drier? Broadening out from discussing snowfall, was unusually wet from the Southwest into the upper Midwest, but skewed drier in parts of the Southern Plains and Florida.

L​ooking at past stronger El Niños, here are two potential significant changes this season:

-​ Wetter: Florida to Texas.

-​ Drier: Parts of the Ohio Valley.

Departures from average precipitation (rain, melted snow) from November through April during nine stronger El Niños since 1950.

(NOAA/PSL)

T​hat means . Keep this in mind if you are a snowbird migrating from colder climates looking for sunshine and a break from the winter blahs.

F​or other wetter parts of the South, that could also mean more snow and ice events if enough cold air happens to be in place when the aforementioned turbocharged southern branch of the jet stream is active.

H​ow could this El Niño change this season's temperatures? Last season, with a persistently chilly West and Northern Plains but generally milder rest of the Lower 48 states dominated.

Two potential significant changes possible this season, if the majority of past El Niños are an indication, include:

-​ Milder: Pacific Northwest, northern Rockies.

-​ Colder: Much of the South.

Same as above, but departures from average temperatures (rain, melted snow) from November through April during nine stronger El Niños since 1950.

(NOAA/PSL)

B​ut it's not just El Niño. Now we've come to the caveats and asterisks.

F​irst, not all El Niños are exactly the same. Even a stronger El Niño doesn't necessarily guarantee strong impacts on the weather pattern.

J​ust as the price of gasoline doesn't control the entire economy, El Niño isn't the only factor influencing winter weather.

Other ingredients could throw a monkey wrench into the scenarios we described above.

T​he Greenland Block

One is the degree to which blocking in the upper levels of the atmosphere occurs near Greenland this winter.

When high pressure aloft forms near Greenland, it blocks the west-to-east flow of the jet stream, forcing it to take a sharp southward plunge into the eastern U.S.

The area of blocking high pressure near Greenland forces a southward plunge in the jet stream across the eastern states when the North Atlantic Oscillation is in its negative phase. This leads to persistent cold temperatures and the potential for East Coast snowstorms.

Known to meteorologists as a Greenland block, this pattern delivers ample cold air from Canada and is an instigator for East Coast snowstorms.

How often this pattern develops in any winter season is difficult to forecast months ahead of time.

But if the Greenland block sets up frequently during a stronger El Niño winter, parts of the Southeast and mid-Atlantic can have a colder, snowier winter. This happened in the strong El Niño of 2009-10, and delivered than the typical strong El Niño average discussed earlier.

T​he Polar Vortex

Another winter wild card difficult to forecast months in advance is the polar vortex, a whirling cone of low pressure over the poles that is strongest in the winter months.

When the polar vortex weakens, the cold air typically trapped in the Arctic can spill out into parts of Canada, the U.S., Asia and Europe because the jet stream becomes more blocked with sharp, southward meanders, sending more persistent cold air southward toward the mid-latitudes.

One such event triggered the that crippled parts of the Plains, overriding the overall warm winter typically seen in the South during La Niña.

Example of a weak polar vortex in winter.

This stronger El Niño gives us a bit more confidence it will have an influence during the colder months ahead. Time will tell how much these other factors will muddy up that picture.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. His lifelong love of meteorology began with a close encounter with a tornado as a child in Wisconsin. He studied physics at the University of Wisconsin-Madison, then completed his Master's degree working with dual-polarization radar and lightning data at Colorado State University. Extreme and bizarre weather are his favorite topics. Reach out to him on X (formerly Twitter), Threads and Facebook.

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