You’re not going to like this snowfall forecast from Philly to Boston

Computer model projection showing a deep trough, or dip, in the atmospheric flow over the East Coast.
Image: weatherbell analytics

After basking in 70-degree temperatures in February, residents of the Mid-Atlantic and Northeast are in for one heck of a rude awakening early this coming week, as a powerful storm takes shape off the East Coast.

While there is still considerable uncertainty in the details a little over two days in advance, it’s clear that areas from Philadelphia to Boston stand a decent chance of getting walloped with heavy snow, strong winds, coastal flooding and possibly, for a time anyway, heavy rain.

Whether or not the nation’s capital, which has had a measly couple of inches of snow so far this season, sees much from this event is unclear, as is exactly how long the storm lasts.

GFS computer model projection showing a powerful storm just off the East Coast on Tuesday.

The key ingredients appear to be assembling for a major snowstorm that affects tens of millions. First, an Arctic high pressure system is moving into position across southeastern Canada and northern New England, so the cold air will be in place for snow.

Second, two atmospheric disturbances, one riding the northern jet stream out of Canada, and the other surfing the southern jet from the Gulf of Mexico, appear destined to meet up and combine forces to form a single, strong storm.

Probability of greater than 12 inches of snowfall through Wednesday, from 51 different runs of the European model.

Image: weatherbell analytics

However, computer models have not yet locked onto the exact details of this atmospheric mating ritual, known to meteorologists as “phasing.” Subtle shifts in timing and the location of one of these systems can make a big difference in where the surface low pressure area forms and where it moves.

For example, a more offshore track, as hinted by computer models on Saturday afternoon, could spare areas northwest of New York City and Boston from the heaviest snow.

Blizzard watch for NYC, Boston

With the potential for a crippling snowstorm in the nation’s biggest cities, the National Weather Service is not taking any chances. Winter storm watches have been issued for Monday night through Tuesday night from New Jersey north into New England, and a blizzard watch is in effect for New York City, Long Island, coastal Connecticut and coastal Massachusetts all the way into the city of Boston. However, snowfall may continue into Wednesday in many areas.

Model projection showing a deep trough associated with a storm across the northeast on March 15, 2017.

Image: weatherbell analytics

Blizzard conditions have a specific meteorological definition, requiring three straight hours or more with snowfall that reduces visibility to one-quarter mile or less, along with sustained winds of at least 35 miles per hour.

The blizzard watch indicates that forecasters believe these conditions may be met in coastal areas of southeastern New York and Connecticut as the storm strengthens and passes nearby on Tuesday in particular.

If the center of the storm hugs the coast, then a mix with or change to rain could occur along the coast, lowering snowfall amounts and making blizzard conditions less likely. This scenario is looking less likely, though, compared to a more offshore track that would keep most coastal areas all snow.

The period of greatest concern is from Monday evening through Tuesday evening in New York, though the storm could last straight through Wednesday and perhaps even longer in New England.

For areas that stay all snow, well over a foot is likely to accumulate in what would be the heaviest snowstorm of the season for many. In fact, 2 feet of snow is not out of the question in some few spots, particularly across Long Island, parts of New Jersey, and in Massachusetts, depending on the exact storm track.

The National Weather Service is forecasting snowfall totals of a foot to a foot and a half in New York, though the forecast totals are likely to shift somewhat before the storm begins.

Editor’s note: This post will be updated as new data comes in.

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