Like a dam failing, the barrier holding back the winter’s most potent Arctic air swung wide open this week. Below-average temperatures are spilling across the eastern United States, delivering waves of bone-chilling air and blustery winds that began Thursday and are expected to continue well into next week.
This cold snap is arriving at the peak of the winter calendar, fueled by a rare atmospheric setup. While records for all-time lows most likely won’t fall, the arrival of subfreezing air in places unaccustomed to it has recently prompted uncertain forecasts from meteorologists and a sense of restless anticipation from Atlanta to New York.
“It’s been so lackluster these past few seasons,” said Dominic Ramunni, a meteorologist for the National Weather Service in New York. “Any mention or potential for snow kind of perks people’s ears up.”
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 cold is not an aberration; it is a return to form. “This is the dead of winter,” Mr. Ramunni said. In New York, he said, “next week is climatologically the coldest week of the year.” On Tuesday, Central Park is likely to record its coldest high temperature since last January, with some nearby areas struggling to climb out of the teens.
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.
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 this system pushes through from Friday into Saturday, light snow may fall across the Midwest and the Northeast and down the spine of the Appalachians. But the real variable is a second storm that could form Saturday afternoon or Sunday morning off the Southeast coast. If that low-pressure system tracks closely enough to the shoreline, a nuisance cold snap could transform into a significant snow event for coastal cities as far south as Flordia.
The Scenarios: Nothing, Maybe — or a Surprise
Because the storm system in question hasn’t fully formed yet, forecasters are working with hypotheses rather than certainties.
In the Deep South, Mr. Willis said on Thursday, it was “starting to appear at least somewhat possible that at least portions of Georgia could get frozen precipitation.” Models have flirted with the idea of snow stretching from the Gulf Coast of Alabama to the Atlantic Coast of South Carolina.
Farther north, the area along Interstate 95 remained a question mark on Friday. Mr. Ramunni said the most likely outcome for New York City on Sunday is “some noticeable snow, but not impactful.” But he cautioned that the outcome hinges entirely on the storm’s track; a shift of just 50 miles could be the difference between a dusting and a headache.
The only sure thing this week? Snow around the Great Lakes. Because the lakes have not yet frozen, the arrival of Arctic air will set off lake effect snow. “You’re going to have a lot of lake effect snow,” Mr. Snell said, predicting a long duration of snowfall from Michigan to upstate New York through the first half of next week.
There remains a distinct possibility that the weekend turns out to be a bust for snow lovers. One reliable computer model has consistently shown a drier, lower-end outcome with no accumulation in the South. Just earlier this week, models teased a major nor’easter that never materialized.
However, there is still a more prolific outlier. If the storm intensifies more quickly than forecasters expect, some models suggest several inches of snow could blanket the South. It is a scenario that emergency managers must prepare for, even if meteorologists think it unlikely.
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.”
Mr. Ramunni 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.
Judson Jones is a meteorologist and reporter for The Times who forecasts and covers extreme weather.
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