Philly’s winter should be light on snow, forecasters say, but La Niña’s impact is still unclear

The winter once again is expected to be gentle on home heating costs and on highway department budgets around Philadelphia, NOAA reiterated Thursday in updating a seasonal outlook that is very much in line with the consensus among meteorologists.

But forecasters are giving the region’s snow lovers at least a snowball’s chance of receiving a measure of satisfaction, and the climate center says that it expects the meteorological winter, which begins Dec. 1, to get off to quite a cold start in the Northeast and much of the nation.

Those willing to venture guesses on how much snow will land upon Philly expect that while the total will fall short of the annual average, 23.1 inches, it should exceed last season’s paltry 11 inches.

One factor forecasters have all mentioned is the anticipated cooling of surface waters over a vast expanse of the equatorial Pacific — La Niña. But, so far, it’s more like La Nada out that way, with temperatures near normal.

Other factors are very much in play, but in terms of clues to the U.S. winter, what happens in that region of the Pacific is “still the biggest thing in the room,” Matt Rosencrans, seasonal forecaster with the climate center, said Thursday.

Sea-surface temperatures in the equatorial Pacific affect the overlying air and the upper-air winds that carry weather to the United States.

The ocean is slow to cool and to warm, thus its impacts can endure for a season. When the ocean is cooler than normal, on average the upper-air patterns would favor storms passing north of the region, arguing against the classic nor’easter coastal storms that are the region’s major snowmakers.

Rosencrans said that sea-surface temperatures in the equatorial Pacific can account for 30% to 35% of the reasoning in the climate center’s outlooks.

The second-biggest “signal,” he said, would be the climate trends, which argue for warmth in the East. Those trends were a significant player in the updated December-through-February outlook, which favors above-normal temperatures in the Philly region and elsewhere.

The climate center says it still expects a La Niña to develop, but it likely would be weak and of short duration.

Paul Pastelok, the longtime seasonal forecaster with AccuWeather Inc., said trade winds have inhibited La Niña development, adding, “It’s getting too late.” That said, he is sticking with his forecast of 15 to 20 inches of snow for Philly.

Snow is an elusive climate indicator, since one storm can generate a season’s worth of snow.

The current “normal” snowfall, based on the 1991-2020 period, of 23.1 inches for Philly, actually is greater than that of the cooler 1980-2010 period, 22.1 inches.

In Philly’s annual snow totals — ranging from a “trace” in 1972-73 to 78 inches in 2009-10 — good luck finding a pattern.

Historically, Philly has experienced clusters of years in which snow was scarce, such as this one of recent years. Only one winter of the last six had normal snowfall, with just 0.3 inches measured in 2019-20 and 2022-23.

Philadelphia had a stretch of snow-starved winters in the 1880s, and nine consecutive seasons of well-below-average snow ending with the winter of 1931-32.

In the early 1950s, snow deprivation in the Northeast was a major impetus in jump-starting the snow-making business in ski resorts. Is this another low-snow era?

“I feel like we’re in that period,” said Kathy Orr, veteran meteorologist for Fox29, which is predicting a precise 17 inches in Philly. She believes that clusters of low and high snow years may be tied to slow changes in the Pacific.

Rosencrans suggested she may be on to something. “The ocean really controls the atmosphere on longer-term time scales,” he said.

Citing major changes in upper-air patterns, the climate center now sees a high likelihood of below-normal temperatures in the East through Dec. 5. Whether that would mean snow is another matter.

Judah Cohen, a polar scientist with the climate analytics company Atmospheric and Environmental Research, based in New England, an unabashed snow lover, said winter-philes should enjoy the cold while it lasts.

The longer-term outlook, he said, “favors a milder pattern.”