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Nor’easter, ‘bomb cyclone’ to deliver heavy snow, wind to East Coast

Blizzard conditions and power outages are possible in eastern New England on Saturday

Snowfall forecast from the National Weather Service. (WeatherBell)
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This article, first published late Thursday morning, was updated in the evening based on the latest snowfall projections.

Less than two days remain before a major winter storm rocks the Northeast and coastal Mid-Atlantic, and fluctuating snowfall forecasts are starting to come into better agreement. Consensus is building that a major winter storm — and possibly a blizzard — is poised to plaster coastal areas from Delaware to Maine.

A number of locations are almost certain to see more than a foot of snow. That’s most likely in coastal Maine or in eastern Massachusetts, particularly from Boston to Cape Cod. Totals nearing two feet with blizzard conditions can’t be ruled out there.

Farther south, cities like Hartford, Conn., New York and even Salisbury, Md., and Virginia Beach could be in for a hefty snowfall, but confidence in double digit totals decreases south of eastern New England.

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Winter storm watches, affecting more than 45 million people, stretch from coastal North Carolina and the Virginia Tidewater all the way northeast to eastern Maine. The watches include Virginia Beach; Richmond; Dover, Del.; Philadelphia; New York; Hartford; Providence, R.I.; Boston; Worcester, Mass.; and Portland.

Watches have been upgraded to warnings for parts of the Delmarva Peninsula and coastal New Jersey, including Ocean City, Md. and Atlantic City.

In addition to heavy snow, some residents of Rhode Island, southeastern Massachusetts and coastal Maine and New Hampshire will see a 1- to 3-foot ocean surge as the storm pushes water toward the coastline. The surge, combined with high astronomical tides, could spur flooding and beach erosion. Strong to damaging winds are possible, too, with gusts topping 60 mph on the Cape and Islands.

The town of Scituate, Mass., is calling for voluntary evacuations of residents occupying vulnerable beachside homes.

“Travel could be very difficult to impossible,” wrote the National Weather Service office in Boston. “Strong winds could cause tree damage.”

The setup

A pair of “shortwaves,” or high-altitude lobes of cold air, low pressure and spin nestled within dips in the jet stream, were rolling southeast across North America on Thursday. The first was over Montana, and the second was slipping through northern Alberta. Both will overlap and “phase” on Friday.

That approaching upper-air kicker will energize a zone of low pressure offshore of the Carolinas beginning Friday afternoon. As that low treks northeast, it will undergo “bombogenesis,” or explosive intensification. In fact, it will more than meet the requisite breakneck pace to qualify as a “bomb cyclone,” its minimum central air pressure set to plummet.

That will enhance the storm’s winds and precipitation as the counterclockwise-swirling low tosses snow back at the coast. Near the waters, a heavier, wetter snow is likely, but temperatures in the teens and 20s inland should favor a lighter snow with a greater fluff factor.

Sources of uncertainty

For a storm barely 48 hours away, a bombardment of conflicting information has led to a highly uncertain forecast along the Acela corridor, the most densely populated stretch of the country. Forecasters are still unsure about two key factors in the storm’s development that will have huge implications on the distribution of snow amounts:

  • When the system gets going. In other words, meteorologists are not sure whether “phasing” will occur earlier, and allow low pressure to develop closer to the coast, or if it will be delayed. An earlier phasing would deposit moderate to heavy snows in southeast Virginia, the Delmarva Peninsula and coastal New Jersey.
  • Where the storm tracks. The American (GFS) model has been consistent in allowing the storm to slip more out to sea, which would reduce or eliminate snow for most except those inside Interstate 495 in southeastern New England. The European model, farther west in its simulations, projects heavy snow in the Big Apple.

The maps below from the National Weather Service, projecting the probability of warning-criteria snow and the magnitude of storm impacts, are a useful guide to where the storm will be most serious:

Jackpot totals in eastern New England

Plymouth and Bristol counties in Massachusetts, as well as the Cape and the Islands, could see some of the heaviest snowfall totals. A general 16 to 20 inches is possible there, with an outside shot at two feet. Thundersnow can’t be ruled out, either, during the height of the storm Saturday afternoon.

One to two feet is probable in Boston and the storm total could rank among the biggest on record during January or any month if amounts reach the upper end of predicted ranges.

Light snow will overspread Connecticut, Rhode Island and areas south of the Mass Pike during the predawn hours Saturday, becoming moderate to heavy by sunrise. There may be some mixing with sleet on the outer Cape and Nantucket initially.

Snow may fall at a rate of 1 to 2 inches per hour briefly in the heaviest band far southeast near the storm’s center, while moderate snows expand through most of New Hampshire and Maine during the late-morning to noontime hours. Damaging winds of 60 to 75 mph on Cape Cod and 40 to 50 mph elsewhere within a county or two could make for blizzard conditions with reduced visibilities and result in scattered power outages.

There’s also a risk of coastal flooding, particularly during the Saturday evening high tide. Typically prone locations such as the Sandwich Boardwalk, Buzzards Bay, Barnstable Harbor, Narragansett Bay and Scituate Harbor ought to be closely watched.

Snow will taper southwest to northeast Sunday morning.

Here are predicted amounts in eastern New England, which may still require fine-tuning as the storm track comes into focus:

Boston: 12 to 24 inches

Providence: 12 to 24 inches

Worcester: 6 to 12 inches

Hartford: 6 to 12 inches

Manchester, N.H. 8 to 14 inches

Portland, Maine: 8 to 14 inches

A tough call: New York and Philadelphia

In New York City, the odds of a plowable snowfall have increased, but the system doesn’t look to be a blockbuster. The forecast is dependent on how far west a potentially heavy band of snow extends

Whether New York City ends up under that band is the million-dollar question. For now, the Big Apple should plan for flurries or light snow Friday afternoon becoming moderate around 9 or 10 p.m. and lasting intermittently through Saturday evening. That’s assuming a track that’s far enough west. The snow could end considerably earlier if the system trends farther out to sea.

Philadelphia should expect a similar timeline but shifted up about two or three hours. As for its neighbors to the north, amounts may very substantially from west (less) to east (more) across the metro area.

New York City: 5 to 10 inches

Newark: 5 to 10 inches

Philadelphia: 4 to 7 inches

Atlantic City: 6 to 12 inches

If the storm tracks on the east side of forecasts, these amounts will probably be lower.

Sneaky surprise in the Mid-Atlantic?

If the system develops on the earlier end of its range of possibilities, it could easily produce substantial snowfall on the eastern shore of the Chesapeake Bay, the Delmarva Peninsula and toward the Virginia Tidewater.

Light snow breaks out around or just after lunchtime Friday, including in the D.C.-to-Baltimore stretch, and lingers through evening before increasing in coverage and intensity to the east during the evening. The Delmarva Peninsula could see it last through Saturday.

Big East Coast storm to brush D.C. area with snow Friday into early Saturday

Even northeastern North Carolina could wind up with a healthy snowfall.

Here are some initial snowfall projections that could be high or low depending on the storm track:

Washington: Coating to 2 inches

Baltimore: 1 to 3 inches

Richmond: 2 to 5 inches

Virginia Beach: 2 to 5 inches

Salisbury, Md.: 4 to 7 inches

Ocean City, Md.: 6 to 12 inches

Dover, Del.: 4 to 7 inches

Raleigh, N.C.: Coating to 2 inches

Jason Samenow contributed to this article.