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Major winter storm to slam Mid-Atlantic and Northeast midweek, with D.C. on rain-snow dividing line

At least 6 to 12 inches of snow is likely from west-central Virginia to southern New England; wintry mix is most likely in Washington and Baltimore

Canadian model simulation of the storm Wednesday and Wednesday night.
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A major winter storm is set to wallop the Mid-Atlantic and the Northeast on Wednesday and Thursday, with many areas from western Virginia to southern New England expected to see heavy snowfall. But for the immediate Washington area, a messy mix of precipitation is more likely than a major snowstorm.

The storm will take the form of a classic nor’easter, forming near the coast of the Carolinas and crawling up the Mid-Atlantic coast. An area of high pressure over eastern Canada will feed cold air into the storm, and many models show the potential for at least six to 12 inches of snow from west-central Virginia through eastern Pennsylvania into New York City and perhaps into southern New England, including Boston.

But just to the east of this zone, which includes Washington, Baltimore and the eastern suburbs of Philadelphia, enough mild air from the ocean may get drawn inland for snow to flip to ice and rain, limiting accumulations. That said, as the storm pulls away Wednesday night into early Thursday, these areas could see rain and mixed precipitation change back to snow before ending.

The exact position of the rain-snow line is still coming into focus, and there is some chance it holds just to the east of Washington and Baltimore, which would allow for more significant snowfall in these cities and their close-in suburbs.

Detailed overview of the D.C.-area forecast

It is fairly likely that precipitation begins as snow between sunrise and noon Wednesday in the Washington region, except for cold rain in Southern Maryland. During the afternoon, the rain-snow line is likely to push northwest. The question is how far. The range of possibilities spans from Interstate 95 to Interstate 81.

If the rain-snow line doesn’t make much westward progress, this could become a significant snow event for most of Washington’s western suburbs and even in the city. Precipitation is likely to be heavy Wednesday afternoon and evening. But if the rain-snow line scoots toward the mountains, snow amounts will be limited and cold rain will prevail from I-95 eastward with a messy mix in between.

Even if a lot of snow doesn’t materialize west of Washington, low-level cold air may prove difficult to dislodge, creating the possibility of significant sleet or freezing rain. Toward Interstate 81, where mostly snow is likely, at least six to 12 inches is a good bet.

Where precipitation changes to rain and mixed precipitation in the Washington region, it could transition back to snow as the storm pulls away, with accumulation possible overnight Wednesday.

Chance of at least one inch of snow:

  • Front Royal, Winchester, Martinsburg and Hagerstown: 90 percent
  • Warrenton, Leesburg and Frederick: 75 percent
  • Manassas, Reston and Gaithersburg: 65 percent
  • Washington and Baltimore: 55 percent
  • Fredericksburg, Waldorf and Annapolis: 35 percent

Chance of at least three inches of snow:

  • Front Royal, Winchester, Martinsburg and Hagerstown: 80 percent
  • Warrenton, Leesburg and Frederick: 65 percent
  • Manassas, Reston and Gaithersburg: 50 percent
  • Washington and Baltimore: 40 percent
  • Fredericksburg, Waldorf and Annapolis: 15 percent

Chance of at least six inches of snow:

  • Front Royal, Winchester, Martinsburg and Hagerstown: 65 percent
  • Warrenton, Leesburg and Frederick: 45 percent
  • Manassas, Reston and Gaithersburg: 35 percent
  • Washington and Baltimore: 25 percent
  • Fredericksburg, Waldorf and Annapolis: 10 percent

Because the rain-line snow is a moving target, the forecast for the Washington region is a bit of a nightmare. When we consider all of the available model information, we see two most likely scenarios. Which scenario prevails will depend on how quickly the coastal storm develops and its track.

A slower-developing storm that tracks inland favors more rain and less snow, whereas a faster-developing storm that tracks just offshore would help lock in cold air and produce more snow. It’s possible that the ultimate outcome is some hybrid of these two scenarios:

Scenario 1 — Less snow, more mess. Mountain snowstorm. (60 percent)

Low pressure forms near the South Carolina coastline and takes an inland track west of Norfolk. Wet snow moves in around midmorning (except rain southeast of Washington) and quickly changes to rain for the city and points south and east, probably producing no appreciable accumulation.

The rain-snow line would push well west of the city, leaving the I-81 corridor with the heavy snow, possibly amounts approaching a foot. The European and NAM models favor this scenario.

The high-pressure zone over southeastern Canada could keep temperatures right at the ground at or a little below freezing, leading to the potential for freezing rain or sleet in the transition zone between snow and rain west of Washington. Significant snow accumulations might be limited to our far-western area, from Leesburg and Frederick and especially into the mountains.

The rain could end as a brief period of snow Wednesday night in areas that flipped to ice and rain.

Scenario 2 — Major snowstorm along Interstate 95 and west (40 percent)

The low-pressure system develops off the coast of the Carolinas and tracks just offshore the Virginia Capes, with the rain-snow line setting up near the city or a little to the east. The American model supports this scenario.

Snow would develop across the region by midmorning Wednesday, and it would probably fall heavily enough into the afternoon to produce several inches of accumulation in the District. Even in this scenario, the snow in and around the city would probably change to mixed precipitation before changing back to snow that could be heavy enough to produce additional accumulations.

This scenario would hammer areas west of the Beltway and particularly places west of Fairfax, Prince William and central Montgomery counties, which might stay snowy for the duration of the event.

Outlook for Philadelphia, New York and Boston

While the storm looks like a complicated forecast in D.C. itself, the big cities to the north and east that are closer to the cold air source and will be farther north and west of the low-pressure area are under a greater threat for heavy snow.

In Philadelphia, there is the potential for six to 10 inches of snow, depending on the storm’s exact track and intensity, though the National Weather Service notes that mixing with sleet and rain could hold amounts down, especially in parts of New Jersey. Philadelphia’s northwestern suburbs could see a foot or more of snow.

New York may be in one of the storm’s sweet spots, with heavy snow, little mixing with sleet or rain, and strong winds. The Weather Service isn’t yet predicting specific snowfall amounts for the Wednesday storm, but multiple computer models support totals up to or even exceeding a foot, especially from the city on to points north and west.

In Boston, a cold, fluffy snow is likely, but there are questions about whether the heaviest snow bands will make it far enough north to affect the Boston metro or be confined further south.

“This is not a lock,” the Weather Service forecast office in Boston stated in a forecast discussion Sunday morning. At the same time, forecasters stated the odds of accumulating, potentially heavy snow are increasing there. Six inches or more of snow is likely for much of southern New England, particularly in eastern Massachusetts, as well as much of Connecticut and Rhode Island.

Coastal flooding may also be a concern along the New Jersey shoreline and in southern New England as winds pick up due to the air-pressure gradient between the high-pressure area to the north and the coastal low to the south.

Dan Stillman contributed to this article.