Bomb cyclone to bring snow, wind from Tennessee to Maine

Conditions will begin to deteriorate over parts of the Mississippi Valley on Friday before the storm and its Arctic blast hit the East Coast on Saturday, kicking off a 24-hour window of nasty weather. The bull’s eye of snow, with more than a foot possible, looks to stretch from Syracuse, NY, to Burlington, Vt.

Snow was already falling over parts of the Plains states on Thursday morning, and winter storm warnings and winter weather advisories blanket Kansas, Oklahoma, the Texas Panhandle, Missouri and Illinois. Winter storm watches have been issued for the Appalachians, where more than half a foot of snow is likely.

The storm comes on the 29th anniversary of one of the most infamous March storms: the blizzard of 1993. This storm will not be as intense or far-reaching.

Nonetheless, it will rapidly intensify as it slides up the East Coast on Saturday. Its minimum air pressure, an indicator of its strength, could rival that of Hurricane Sandy in 2012 by the time it races through the Canadian Maritimes Sunday and Monday.

Storm to ‘bomb out’ over weekend

Surface low pressure will first begin to manifest over Louisiana and Mississippi on Friday night. By Saturday evening, the storm will be a powerhouse low likely to be in the vicinity of Downeast Maine. It will continue swiftly strengthening into Sunday while barreling north into Canada and evolving into a bomb cyclone.

A bomb cyclone refers to a quickly intensifying storm whose minimum central air pressure falls by 24 millibars or more in 24 hours. That’s equivalent to roughly 2.5 percent of the atmosphere’s ambient air pressure. The disparity in air pressure between inside and outside the storm, or change in air pressure with distance, is what spurs winds. Bombs become powerful vacuums that suck in air from all around to fill their voids, generating strong winds.

It’s probable that the storm’s air pressure could drop below 940 millibars Sunday night into Monday. The American GFS model simulates a drop of 68 millibars in 48 hours. That’s more than 40 percent faster than what’s required to qualify as a “bomb.”

Records for low pressure in the United States will not be in jeopardy, but they could fall in parts of Atlantic Canada:

Since lows spin counterclockwise, southerly winds ahead of it will make the east side the rainy side, with wintry weather on the storm’s backside as chilly northwesterly winds filter in.

Moderate to heavy snow likely

Snow will break out across the Texas Panhandle and Oklahoma around sunrise Friday, expanding northeast and increasing in coverage and intensity during the day. By midnight, flakes will be flying along Interstates 44 and 70 corridors and will reach all the way to the Tug Hill Plateau in New York State. That will represent moisture falling along the cold front.

Arkansas, Tennessee and Kentucky could get a burst of moderate to heavy snow Friday night in tandem with an influx of gulf moisture from the south, with the heaviest snow then riding up the Appalachians during the daylight hours Saturday. It’s even possible that northwest Mississippi sees a garnish of flakes.

Nashville, Lexington, Ky., And Little Rock probably are all looking at a general 1 to 2 inches of snow with a few four-inch totals. Accumulations will mostly be relegated to grassy surfaces, since the high March sun angle and high ground temperatures will be working against it on roadways.

For northern parts of the Cumberland Plateau in Middle Tennessee, central and eastern Ohio, eastern Kentucky, West Virginia west of Interstate 79, and western and central Pennsylvania, 3 to 6 inches is possible with higher amounts possible in the mountains. This zone includes Cleveland and Pittsburgh.

The jackpot zone in northern New York through western Maine could see double-digit totals.

Specific totals will hinge on the storm’s exact track, which is still being sorted out.

From western Pennsylvania to western Maine, the combination of heavy snow and strong winds, gusting over 35 mph, could produce some pockets of blizzard conditions with extremely limited visibility.

Mostly rain and wind for the coast

For cities including Raleigh, NC, Richmond, the District, Baltimore, Philadelphia, New York and Boston, it should be mostly a six-hour window of rain and perhaps some brief heavy downpours. In southern areas and the Mid-Atlantic, the first half of Saturday will be more heavily affected, while coastal New England will see wet weather from late morning through early afternoon. A half-inch to an inch of rain is in the offing.

Winds gusting 25 to 35 mph from the south are likely to precede the cold front and accompany the rainfall. Then, as the front passes after lunchtime Saturday, cold northerly wind gusts will ramp up over 40 mph. The falling temperatures also might help precipitation end as a dash of snow for DC, New York and Boston, though accumulations in the metros proper is not likely. Their west and northwest suburbs have a better chance to see a light accumulation.

Arctic front to bring severe thunderstorms, crashing temperatures

Mild air will precede the system Friday into Saturday, with southerly winds in the “warm sector” of low pressure. That will make for some strong to severe thunderstorms both days, with a chance of damaging winds and a couple of tornadoes.

On Friday, the risk will stretch from north-central South Carolina to the Florida Panhandle and northern parts of the Florida Peninsula, including Tallahassee and Jacksonville, as well as Columbus, SC, and Savannah, Ga. The most acute risk, rated level 3 out of 5 by the National Weather Service Storm Prediction Center, covers the central Florida Panhandle and southern Georgia, and includes Tallahassee and Panama City.

Saturday, the risk area expands from Tampa to Virginia Beach. Storm chances will be focused on the first half of the day, the risk area expanded to include Charleston and Wilmington, NC

A dramatic change in wind speed / direction with height, known as wind shear, could cause storms to rotate. Thunderstorms are likely to be low-topped, so large hail – which requires taller storms – probably won’t be a factor, but damaging winds and a few tornadoes may be.

Temperatures will drop like a rock behind the front. Lows north of the Mason-Dixon Line will be in the upper teens inland on Sunday morning, with a few 20s near the coast. Across the Mid-Atlantic and Southeast, lower 20s to near 30.

While strong gusty winds are likely to evaporate whatever water lingers on the ground, any leftover puddles or damp patches will freeze solid by daybreak Sunday.

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