Major winter storm to brush D.C., Philly and NYC with accumulating snow

March 11 (UPI) -- Winter storm watches and warnings were in effect from the Tennessee Valley through northern Maine on Friday as Mother Nature was preparing to serve up a late-winter blast of heavy snow, wind, rain and plunging temperatures.

With fewer than 10 days officially remaining in winter, more than 150 million Americans across the eastern third of the nation will face some impacts from the storm, including places along the Eastern Seaboard that began the week enjoying a spring preview with record-high temperatures.

AccuWeather meteorologists expect the storm to strengthen rapidly and even bring accumulating snow to the major cities along the I-95 corridor, a development prompted by the forecasters' expectation that cold air will plunge farther east faster than initially expected.

"A fast-moving and rapidly strengthening storm will bring intense weather and dramatic weather changes to the eastern half of the nation, with the most extremes in store for the Northeast," AccuWeather senior meteorologist Dave Dombek said.

From a travel standpoint alone, major disruptions are likely on the roads and for those flying. Flight delays and cancellations are anticipated and could result in ripple-effect impacts across the country.

"The storm will have two distinct sides in terms of temperature and weather," AccuWeather chief on-air meteorologist Bernie Rayno said. The eastern half will be associated with warm air, areas of heavy rain, urban flooding, severe thunderstorms, isolated tornadoes and coastal flooding, Rayno explained. On the other hand, colder air will catch up with the storm, and temperatures will plunge across the interior. That will lead to heavy snow, white-outs and localized blizzard conditions as well as a rapid freeze-up.

Even though the snow portion of the storm is likely to last only eight to 12 hours across the interior Northeast and perhaps just a few hours or less near the coast, impacts will be significant.

"If you live in this red area, I would not be on the roads tomorrow. At all," Rayno said, referring to the map below, which highlights the potential for dangerous travel stretching from Kentucky to Maine. He urged people to be careful on Saturday, stressing that "this is going to be a nasty storm."

The storm will move northward from the central Gulf coast Friday night before it tracks along the Eastern Seaboard on Saturday. Its path will eventually take it into Atlantic Canada later in the weekend.

Following a light to moderate snowfall, on the order of a few inches in portions of the lower Mississippi and Tennessee valleys into Friday night, a swath of moderate to heavy snow will expand northeastward over the Appalachians, including the slopes and valleys that extend to the immediate west from Tennessee to Maine.

Accumulating snow will also reach the major I-95 cities from Washington, D.C., and Philadelphia to New York City, and the blast of winter weather in this zone will unfold in dramatic fashion.

Temperatures on Saturday morning will be in the 40s and 50s along I-95 in the mid-Atlantic and New England ahead of a press of Arctic air. Temperatures will plunge 10-20 degrees in a few hours' time and cause rain to change to snow. By the end of the afternoon on Saturday, temperatures are likely to be close to the freezing mark.

"This could be a situation where there are thunderstorms in the morning and a few hours later it is snowing hard along portions of the I-95 zone on Saturday," Rayno said.

The changeover to snow will be quick along the I-95 corridor from Washington, D.C., to New York City, but snow will take some extra time to accumulate in the most urban areas. It could be raining one hour and snowing hard the next. Accumulations near I-95 are likely to range from a coating to an inch on grassy areas in the cities and the southern and eastern suburbs to 1-3 inches in the suburbs immediately to the north and west.

Areas from northern Virginia to central Maryland, southeastern Pennsylvania, northern New Jersey, the lower Hudson Valley of New York and western Connecticut are likely to have accumulations ranging from 1-6 inches with the most in hilly and/or grassy areas.

Roads are most likely to become slushy and slippery in the northern and western suburbs, but some slushy areas cannot be ruled out in the heart of the cities as well. The extent of slippery conditions along the I-95 corridor will depend on the duration of the snowfall, and, at this time, moderate to heavy snow may come down for only 1-3 hours.

Around Boston, a small slushy accumulation can occur in the city with a coating to an inch just to the north and west and 1-3 inches toward central Massachusetts.

Farther west, across the spine of the Appalachians, the combination of plunging temperatures from the 30s to the 20s and even the teens F in some locations will cause snow to accumulate on the roads and slushy areas to freeze. Snowfall will come down heavily at rates of up to 1-3 inches per hour, causing whiteout conditions. As the storm strengthens, snow will persist for longer across areas farther to the north, allowing snow to pile up even more.

Travel will become treacherous, due to the freeze-up alone, in this zone. Conditions will be particularly dangerous as heavy snow first begins on Friday night into Saturday. Meteorologists say this is the type of setup that can lead to cars sliding off roads, major pileup accidents or potentially leave motorists stranded on highways.

"Blizzard conditions, which occur when the visibility drops below 1/4 mile or less and winds frequently gust to 35 mph or greater for three consecutive hours, are most likely to unfold across northern New York and northern New England on Saturday," AccuWeather senior meteorologist Courtney Travis said.

The intense snowfall could be accompanied by thunder in some areas.

The area likely to receive at least 3-6 inches of snow will broaden from eastern Tennessee and Kentucky to include much of western and central Pennsylvania and upstate New York.

A zone of 6-12 inches of snow is likely to begin in the West Virginia mountains and extend up through the Alleghenies of Pennsylvania and central New York with a band of 12-18 inches of snow predicted across northern New York and northern New England through the Eastern Townships of Quebec. It is within this heaviest snow band and, perhaps across a few locations farther to the south, that the AccuWeather Local StormMax™ of 24 inches is most likely to occur.

Metro areas that are most likely to experience a blast of moderate to heavy snow and freeze-up include Knoxville, Tenn., and London, Ky., which is in the southeastern part of the state. Farther to the north, Charleston, W.Va., and Pittsburgh are forecast to get heavier amounts.

As the storm advances north, the area of heavier snowfall will widen, and places such as Rochester, N.Y., and Burlington, Vt., are expected to pick up 6-12 inches of snow.

AccuWeather forecasters warn that dangers from the storm won't end when the snow tapers off. Blowing and drifting snow will follow the storm as frigid air arrives.

Strong west to northwest winds can trigger power outages and will create painfully low AccuWeather RealFeel® Temperatures.

Winds gusts of 40-60 mph will be far-reaching over the Appalachians and Atlantic Seaboard. AccuWeather Local StormMax™ gusts between 80 and 90 mph are predicted in some coastal locations and over the highest elevations of the Appalachians from Saturday into Saturday night.

By the middle of Saturday night, AccuWeather RealFeel Temperatures will dip into the single digits east of the Appalachians and range from zero to 20 below zero over the Appalachians.

On the storm's warm side, which will generally encompass much of the Atlantic Seaboard, rain and thunderstorms are in store at the onset. While the heaviest rain may last only a few hours in the Interstate-95 corridor from Washington, D.C., to Philadelphia, New York City and Boston, the rain can be heavy enough to lead to street and highway flooding from late Friday night to Saturday morning.

Thunderstorms can occur as far to the north as New England, and some of the heavy downpours could drop the visibility to near zero, making travel along highways dangerous.

The risk of coastal flooding associated with southerly and southeasterly winds will be brief due to the storm on Saturday. However, as powerful winds from the west and northwest kick in due to the rapid strengthening storm, a phenomenon known as blowout tides can occur. In this case, the strong winds will push ocean and bay waters seaward.

Small craft and large vessels could run the risk of striking bottom in the shoals of coastal waterways from Saturday night into Sunday.

Despite all the dramatic and hard-hitting impacts from the storm, the system will move along at a swift pace, and weather conditions will generally improve from west to east from the Mississippi Valley on Saturday to the Atlantic coast on Sunday.