Why The East Coast Blizzard Turned Into Slush

The explanation involves a "warm tongue."

On Monday, forecasts were so dire for the snowstorm approaching the Eastern Seaboard of the US that school districts up and down the coast — including those in Boston, New York, Philadelphia, and Fairfax County, Virginia, outside Washington, DC — preemptively canceled classes amid fears of a blizzard.

The result? In Boston, just 4.5 inches by mid-afternoon. In DC, just 2.5 inches of snow on the White House lawn. And in New York's Central Park, predicted to enjoy anywhere from 1.5 to 2 feet of snow, only about 4 inches fell by time school would have started on Tuesday.

While the storm did not feel like a dud to inland residents hit by more than a foot of snow in northern New Jersey, upstate New York, or eastern Pennsylvania, those in major East Coast cities, braced with refrigerators full of food for the winter storm of the season, felt let down when they drew their curtains and saw not a blinding blizzard but just lots of slush on the streets.

What went wrong? Nothing really, weather scientists say. Weather models simulating the storm ahead of time always showed a wide range of possible snowfall totals. It's the media and government officials that — perhaps prudently or perhaps not — emphasize the worst-case scenario of whiteout blizzards.

"The amount of precipitation that was expected was there. And the winds were strong enough for a blizzard," Bob Henson, a meteorologist at Weather Underground, told BuzzFeed News. "It’s just a matter of a very small difference in temperature."

What caused what would have otherwise been snow to fall as sleet over much of the East Coast was — in the words of another meteorologist, Thomas Downs at the private forecasting firm WeatherBELL — a "warm tongue" of air from the Atlantic Ocean.

“The circulation off of the Atlantic Ocean brought in warm air" over land, Downs told BuzzFeed News. That tongue stretched slightly farther over the East Coast than weather models called for.

That small shift made a big difference in the type of precipitation that hit the ground.

The band of warm winds, sandwiched between the cold, moisture-laden clouds above and cold, ground-level layer of air below, melted the snowflakes and refroze them as ice pellets, turning it into sleet.

How far that warm tongue of air sticks out determines where forecasters draw on weather maps the so-called rain-snow line. But drawing that line several days ahead of time, as the National Oceanic and Atmospheric Administration (NOAA) attempts to do with its weather prediction models, is difficult, according to Gregory Carbin, chief of the Forecast Operations Branch at NOAA.

Evolution of forecast numbers from 4 AM to 9 AM from @NWS highlights sharp rain/sleet/snow line movement by 10s of… https://t.co/IqppDNCvXY

"All the global models are generally still too coarse in resolution to depict the intricacies of the rain/snow line in rapidly deepening cyclones such as this one," Carbin wrote to BuzzFeed by email.

Because sleet does not reduce visibility to the degree that snow does, New York, Philadelphia, and Washington, DC, didn't see the whiteout conditions characteristic of blizzards, as many forecasts warned. And because sleet is so much denser than snow, the precipitation that accumulates on the ground is not nearly as deep.

But all that doesn't mean those clearing driveways are spared.

"The same amount of precipitation fell from the sky, it just took a different form," Downs said. "When you're shoveling it, it's the same amount of weight."

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