At a Glance

A strong El Niño will remain in place through spring.El Niño winters tend to be snowier in parts of the Northeast, but not in others.But El Niño winters with more blocking patterns can be snowier for many.One such winter 14 years ago was a textbook case.Several notable Northeast snowstorms have struck in stronger El Niño winters.

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A​ strong El Niño and the potential for more blocking weather patterns could combine to influence Northeast snowstorms this winter season.

First, an El Niño update. This periodic warming of the equatorial eastern and central Pacific Ocean first developed in June and is the first El Niño in more than four years.

S​ince the end of August, its warm temperature anomalies have pushed well above the threshold of a strong El Niño, at least 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer than average. NOAA's Climate Prediction Center forecasts this .

Sea-surface temperature departures from average (in degrees Celsius) during the week of Nov. 19-25, 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.

M​ajor Northeast snowstorm "season" is here. It's against this backdrop that the season for major Northeast snowstorms is kicking off.

A​s the graph below shows, the 36 Northeast snowstorms that were Category 3 or higher on the since 1956 have happened anytime from December through early March, peaking from late January through February.

The number of Category 3 or higher Northeast snowstorms for each two-week period from December through March, according to the NESIS scale. (Note: If a snowstorm overlapped two periods, it was given 0.5 count in each time period.)

(Data: NOAA/NCEI)

W​hat does a stronger El Niño typically mean for snowfall? The map below from NOAA shows how far above and below average snowfall has been during a typical strong El Niño January through March period.

You can see quite a split in the Northeast. While much of the interior Northeast from western Pennsylvania to parts of New England trend less snowy, parts of the mid-Atlantic from southern New Jersey to Virginia and the southern Appalachians have tended to be much snowier in a stronger El Niño winter.

A turbo-charged southern jet stream track usually brings wetter weather to much of the South, which can then curl northward along the mid-Atlantic coast in a stronger El Niño winter. If there's cold enough air in place, that could fall as snow (or ice) more often than usual.

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)

B​ut it's not just El Niño. As convenient as it would be to stop here, El Niño isn't the only factor influencing winter weather. Other ingredients could throw a monkey wrench into this snowfall scenario.

One is the degree to which a pattern in the upper levels of the atmosphere known as the Greenland block occurs 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. This pattern delivers ample cold air from Canada and sometimes is an instigator for East Coast snowstorms.

How often this pattern develops in any winter season is challenging to forecasters months ahead of time. But if it sets up frequently during a stronger El Niño winter, parts of the Northeast can have a colder, snowier winter.

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.

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

H​ere's what the data shows. We examined seasonal snowfall totals during nine strong El Niños since 1950 for several Northeast cities.

We then parsed out those nine seasons into those which also had frequent Greenland blocking (three seasons) and those that had a lack of blocking (six seasons). Admittedly, it's a rather small sample size.

I​nterstate 95 Contrasts

S​nowfall was generally less during a strong El Niño winter from New York City northward. Boston saw an average reduction of almost 25% in snowfall during a strong El Niño.

It was a much different story in the mid-Atlantic states. Both Philadelphia and Washington, D.C., saw markedly more snow on average in a strong El Niño winter.

I​t gets even more interesting when adding Greenland blocking to the mix.

S​trong El Niño winters with frequent Greenland blocking (labeled as -NAO in the graph below) were much snowier than average in New York City, Philadelphia and Washington, D.C. But, as alluded to earlier, there were only three such winters since 1950.

So those Greenland blocking/strong El Niño totals are biased somewhat by , which shattered records in the mid-Atlantic states.

If Greenland blocking is strong this winter, it would be quite the change in the mid-Atlantic from last winter. Both Philadelphia (0.3 inches) and Washington, D.C. (0.4 inches), had one of their least snowy seasons on record in 2022-23, during a weakening La Niña.

B​y contrast, strong El Niños without much Greenland blocking were far less snowy than average along the I-95 corridor.

Seasonal snowfall during all strong El Niños (yellow bars), strong El Niños without Greenland blocking (red bars), strong El Niños with frequent Greenland blocking (blue bars), compared to 1950-2023 average (gray bars) in four major Northeast cities along the Interstate 95 corridor.

(Data: NOAA; Graph: Infogram)

Interior Northeast

O​ver the rest of the Northeast, we noticed a reduction in snowfall during stronger El Niños in most areas, consistent with the map we showed earlier.

A​nd most areas also saw the bump up/bump down we noted along the I-95 corridor for those strong El Niño winters with frequent/little Greenland blocking, respectively.

O​ne notable exception to this was in northern Maine. While each strong El Niño exhibited an average reduction in snowfall of around 10% in Caribou, Maine, the amount of Greenland blocking didn't make much difference there.

Same as the previous graph, but for interior Northeast cities from Pennsylvania to Maine.

(Data: NOAA; Graph: Infogram)

As with financial investments, past snowfall during strong El Niños doesn't guarantee this winter's results. It will be fascinating to see how winter 2023-24 measures up.

M​ORE ON WEATHER.COM

-​ The I-95 Northeast Snow Drought

-​ What To Know About Snow Maps On Social Media

-​ 6 Changes A Stronger El Niño Could Bring This Winter

-​ How El Niño Got Its Name

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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