A winter storm brought light snow to the Northeast on Saturday, from Northern Virginia to western Massachusetts, moving eastward as potent arctic air from Canada spilled behind it.
As of 1 p.m., one to three inches of snow had accumulated in northern Maryland, two to five inches in eastern Pennsylvania, and there were reports of up to four inches in north central Massachusetts, according to Joe Wegman, a meteorologist with the Weather Prediction Center.
Mr. Wegman said that the big cities were getting mostly rain on Saturday, but a second stronger storm was likely to bring snow to Washington, D.C., New York City and Boston on Sunday.
New York City is likely to record two to four inches of snow and Boston three to five. The storm is also expected to bring rare snowfall to parts of the Southeast.
Like a dam failing, the barrier holding back the winter’s most potent arctic air swung wide open this week.
While records for the lowest temperatures were unlikely to fall, the arrival of subfreezing air was expected to bring snow to places unaccustomed to it.
The storm that’s poised to arrive in the Southeast by Saturday night and then push into the Northeast on Sunday could bring accumulating snow as far south as Georgia.
In the Deep South, where a single snowflake icon on a weather app can set off a run on grocery stores, the mood is similar.
“It can get people a little excited,” said Ryan Willis, a forecaster for the National Weather Service in Atlanta.
The Setup
The cold is already here, but it will ebb and flow as different “pulses” move through, according to Cody Snell, a meteorologist with the Weather Prediction Center. Overall, however, the East Coast will remain anomalously cold through most of next week.
On Tuesday, Central Park is likely to record its lowest high temperature since last January, with temperatures in some nearby areas struggling to climb out of the teens.
The primary driver is a near-record-strength ridge of high pressure over the West Coast and Western Canada — essentially an area of higher pressure in the upper atmosphere.
Mr. Snell explained that as the jet stream hits this ridge, it is forced far north into the Arctic before plunging back down, “allowing that air to flow from the Arctic through central Canada into the East.”
As a system pushed through on Saturday, light snow fell across the Midwest and the Northeast. But the second storm that’s forming in the Gulf off Louisiana is more notable and is expected to bring snow to portions of the Southeast, Mr. Wegman said.
“That area can easily go multiple winters in a row without seeing snow,” he said. “It is unusual.”
There will likely be some snow flakes in the Florida Panhandle, but they’re unlikely to stick to the ground. Accumulations are most likely from south-central Georgia to points northward.
“It’s going to be a fraction of an inch of accumulation, but because southern Georgia isn’t used to getting snow, it will cause traffic and problems on roads,” Mr. Wegman said.
The snow is likely to fall in the Southeast late Saturday night into early Sunday, with the storm pushing north into the Mid-Atlantic and New York City early on Sunday morning and arriving in southern New England by midmorning.
A ‘Perfect Alignment’ Problem
Forecasting snow in the South is famously difficult because it requires a perfect alignment of ingredients.
“You need the cold and the moisture to arrive at the exact same moment,” Mr. Willis said, noting that such a synchronization “doesn’t happen every winter in this part of the country.”
The data itself is part of the problem.
Mr. Snell noted that because much of this air is originating in the Arctic — a region with fewer observational weather stations — computer models can be “fickle.”
Dominic Ramunni, a meteorologist for the Weather Service in New York, compared the process to the butterfly effect.
If you make even small changes to the initial conditions fed into a model, the potential outcomes can vary greatly.
The stakes for getting snowstorms right are higher than with any other type of weather. If a rain forecast is off by three-quarters of an inch of liquid, most people won’t notice.
“But if a snow forecast is off by that same amount of liquid, it’s the difference between a minor dusting and a foot of snow,” Mr. Ramunni said.
Aimee Ortiz contributed reporting.
Judson Jones is a meteorologist and reporter for The Times who forecasts and covers extreme weather.
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