A storm forecast to undergo rapid strengthening will bring drenching rain, coastal flooding and heavy interior snow to part of the Northeast and may become the next bomb cyclone to affect the United States to end the week.

In order for the strengthening storm to be dubbed a bomb cyclone, the barometric pressure at the center of the storm must plummet 0.71 of an inch of mercury (24 millibars) in 24 hours. This storm may reach that criterion as it moves northward and intensifies from Thursday evening near Delmarva to Friday evening in southern Maine.

The storm is not expected to approach the strength and size of the massive bomb cyclone that hit the Central states last week. However, the rapid strengthening will have implications with threats to lives, property, and travel.

Storm to produce localized flooding

Rain will continue to develop and become heavier as it pushes northward along the Interstate 95 corridor and even through many of the northern and western suburbs of Washington, D.C., Baltimore, Philadelphia, New York City and Boston spanning Wednesday night to Friday.

While major flooding is not expected from eastern Virginia to Massachusetts and southeastern New Hampshire, enough rain may fall at a fast enough pace to slow travel and trigger urban and poor drainage area flooding.

A brief period of stiff east to southeasterly winds will accompany the rain as it spreads northward. These winds will push some water onshore, which can lead to minor coastal flooding. However, the highest winds from the storm will occur on the backside and from the west and northwest.

Snow cover may liquefy in Maine

Heavy rain and rapidly melting snow are likely to trigger substantial flooding in central and southeastern Maine.

As of Wednesday morning, there is from 1 to 8 inches of water locked up in the existing snowcover in the state.

Small streams and rivers will rise rapidly. Ice jams are also likely. 

Snow to blanket northern New England; High-elevation snowfall risk in central Appalachians

Just enough cold air will invade the storm to allow a substantial snowfall over the mountains and in some of the valleys of northern New England.

"The heaviest snow, on the order of 6-12 inches with an AccuWeather Local StormMax™ of 16 inches, is forecast from the Adirondacks of northeastern New York state, the Green Mountains of Vermont and the White Mountains of northern New Hampshire," according to AccuWeather Senior Meteorologist Brian Wimer.

In these areas, the bulk of the snowstorm will occur from late Thursday night through Friday night.

Heavy snow is also in store over the eastern townships of Quebec and northwestern New Brunswick as a general 15-30 cm is forecast from Friday to Saturday.

Farther southwest, marginal temperatures will allow a combination of rain and wet snow from the Allegheny Mountains of west-central Pennsylvania to parts of the Poconos in northeastern Pennsylvania, the Catskills of southeastern New York state and the Berkshires of western Massachusetts and northwestern Connecticut.

The higher terrain in these areas may receive up to several inches of snow, while a coating to an inch or two of slush may fall at lower elevations during the height of the storm late Thursday night to Friday morning.

Rain showers, snow showers, and heavier snow squalls to follow the storm

Motorists and pedestrians should be prepared for rapidly changing weather conditions from Friday to early Saturday, even where the main storm totally missed their location or areas that received only rain.

In addition to high winds with gusts as high as 60 mph as the storm lifts northward and strengthens, very cold air aloft will pivot southeastward and trigger gusty rain showers with small hail in some areas and heavy snow squalls in others.

Snow showers and heavy snow squalls will pivot across the central and eastern Great Lakes to the central Appalachians on Friday. The heavier snow squalls may not only cause a dangerous sudden drop in visibility for motorists on the highways but also could bring a small, but rapid accumulation that makes roads and sidewalks slippery.

As these squalls wander farther to the southeast, where the air is slightly warmer east of the Appalachians from the mid-Atlantic to southeastern New England, rain showers can occur. However, these can be heavy and gusty and may contain hail or soft chunks of ice called graupel.

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