A potentially disruptive winter storm expected to move across the eastern United States later this week could bring snow to the Appalachians, the Mid-Atlantic and the Northeast, but forecasters warned on Monday that it was too early to know exactly how the complicated system would unfold.
Here’s what forecasters know.
After a stretch of unseasonably mild weather over the eastern United States, cold air was forecast to push south from Canada beginning Wednesday. That will set the stage for a storm to develop that could bring a wintry mix before changing to snow across parts of the Mid-Atlantic and New England on Thursday and Friday, according to forecasters.
The storm’s evolution depends largely on where it forms, a detail on which some weather models currently disagree.
Here’s what they don’t know, yet.
Bob Oravec, a meteorologist at the Weather Prediction Center, said some forecast models showed the storm forming over land, while others had it offshore. When forecast models agree in the lead-up to a storm, meteorologists can be fairly confident when they start to tell people what it will probably do. But when the models predict a broad range of outcomes, as they are here, each day closer to the storm brings a slightly better sense of what is likely to happen.
“If it forms inland, all the major cities will get almost nothing,” Mr. Oravec said. “All the snow will be way north across western New York State, northern New York, northern New England.”
But an offshore storm, he said, could result in snow for big cities including Philadelphia, New York, Boston and Washington, D.C. It’s this possibility that has generated attention to the storm at the start of the week, even if it remains far from certain.
Other uncertainties this early include the storm’s strength, timing and exact path — factors that forecasters said could determine whether coastal cities see snow and strong winds or heavy rain.
“The real big question mark is along the Interstate 95,” said Richard Bann, a meteorologist at the Weather Prediction Center.
Snow is nearly certain around the Great Lakes.
Despite those uncertainties, forecasters said snow was increasingly likely in areas farther inland, as temperatures drop. Mr. Bann said snow was “fairly certain” over parts of the lower Great Lakes, the central Appalachians and the interior Northeast from late Wednesday, including areas of Illinois, Indiana, Ohio, Pennsylvania, New York and Maryland.
“Then much colder air will develop over the Great Lakes,” he said. “And we’ll start getting a lot of lake-effect snows in some of the typical places.”
Forecasters said clearer details of the storm’s development should emerge over the next few days.
“That will help us pin down where the heaviest precipitation occurs and when,” Mr. Bann said.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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