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A bomb cyclone could slam eastern U.S. on Saturday with wintry blast

Strong winds to rock much of eastern U.S. amid plummeting temperatures, with possible blizzard conditions in interior Northeast

Depiction of precipitation Saturday morning from the European model. (WeatherBell)

Despite record highs in the 70s and 80s in the eastern United States on Monday, winter looks like it’s not over. A probable bomb cyclone will take shape along an Arctic front sweeping toward the East Coast late Friday into the weekend.

Temperatures will plummet as winds rage and, from the central Appalachians to the interior Northeast, significant snowfall is probable. Blizzard conditions could even develop in some areas.

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Models have been coming into better agreement about the yet-to-develop storm, which will strengthen from a weak surface wave to a full-fledged cyclone as it moves up the Eastern Seaboard on Saturday. Wind gusts to at least 40 to 50 mph are possible in the Mid-Atlantic and the Northeast.

A strong cold front, which could bring heavy rainfall, plummeting temperatures and thunderstorms in some areas, will precede the system.

The frigid air plunging south from Canada will cause temperatures to be 15 to 40 degrees colder than normal in the Rockies, the Plains and the Midwest by Friday morning; the Great Lakes, the Mississippi Valley and the South on Saturday morning; and the East Coast by Sunday morning. This translates to lows in the single digits in Minneapolis on Friday, in the teens in Detroit and Chicago on Saturday, and in the teens and 20s (single digits in the mountains) in much of the Northeast and Mid-Atlantic on Sunday.

The setup

Late this week, two disturbances, one in the Southwest and another over southern Canada, will merge over the Midwest, forcing the jet stream to plunge southward and dragging frigid air toward the East Coast.

That will pave the way for a more robust disturbance to barrel southeast out of northern Canada on Friday, slipping over the Great Lakes and passing over New York, Pennsylvania and New England.

As this third disturbance merges with the previous two, an intense zone of low pressure or coastal storm will develop along the Arctic front parallel to the East Coast, probably just offshore the Mid-Atlantic.

The low-pressure zone is forecast to strengthen speedily enough to be classified as a “bomb cyclone.” Some models project that by the time it sweeps into eastern Canada, its pressure could drop as low as Hurricane Sandy in 2012 — about 940 millibars. Mid-latitude cyclones such as this one spread their impacts over a broader area, so are generally less severe than tropical systems.

Models project that the strongest winds from this system will occur over the Atlantic Ocean and Canadian Maritimes, where hurricane-force winds could develop. However, widespread gusts over 40 mph, with localized gusts to 50 to 60 mph, especially near the coast, are possible in the Mid-Atlantic and much of the Northeast during the day and night Saturday.

Tennessee Valley and central Appalachians impacts

As the Arctic front charges from the Midwest toward the Ohio and Tennessee valleys and central Appalachians, a band of snow will develop in its wake. Several inches could fall during the day and night Friday from the high elevations of western North Carolina and the Smoky Mountains through eastern Kentucky, eastern Ohio, West Virginia and western Pennsylvania.

Some snow could even fall south of that into northwest Georgia and northern Alabama and Mississippi, but confidence in flakes that far south is low.

Temperatures in this zone will drop from the 50s on Friday to the teens and 20s by Saturday morning.

Mid-Atlantic and Southeast impacts

Ahead of the storm, Washington may approach 60 degrees Friday afternoon, with Richmond in the lower 60s.

Heavy rain and possible thunderstorms are anticipated in the Mid-Atlantic on Saturday morning as the cold front arrives.

While instability, the “juice” that fuels thunderstorms, may be very hard to come by, there will be plenty of shear or a change of wind speed and/or direction with height. That is likely to brew a line of downpours with embedded pockets of gusty winds along the front. Timing is tricky to nail down, but it may be in the 6 a.m. to 10 a.m. time frame for the Washington to Baltimore stretch Saturday.

Over the southeastern United States, in parts of Florida, Georgia and the eastern Carolinas, a small tornado threat could materialize Friday night into Saturday.

Cold air pours southeast behind the front, potentially flipping rain over to a brief period of snow in the Mid-Atlantic where temperatures may drop from the 50s to near freezing in just a few hours. Whether any snow accumulates is uncertain.

Then winds will ramp up as the low starts sucking in more air upon its exit, with gusts over 40 mph possible from the day into the night Saturday.

There should be a considerable warm-up thereafter toward the middle of next week.

Coastal Northeast impacts

The Arctic front will sweep through western New England and New York City on Saturday morning, but places such as Boston, Providence and Cape Cod could hang on to the upper 40s or lower 50s as they remain in a tiny warm sector east of the developing storm’s center.

The day will begin wet and end white as sharply falling temperatures through the 30s allow precipitation to change to snow. The timing of the change should keep all rain in the cards until 3 p.m. or 4 p.m. for Boston, and perhaps even later across Downeast Maine, which will be the last to relinquish southerly winds on the system’s warm side.

Winds will howl, probably gusting over 40 or even 50 mph Saturday afternoon and evening. The strongest gusts are expected near the coast.

Interior Northeast impacts

The interior Northeast could be hit hardest by this system Saturday, especially from northeast Pennsylvania through much of interior New York, Vermont, northern New Hampshire and inland Maine.

Significant snow accumulations of a half foot or more are possible. Uncertainty remains sky-high, however, so no reliable snowfall forecasts can be made yet.

As wind gusts may easily top 35 to 40 mph, blizzard conditions could develop.

The storm will be fast-moving, with precipitation rapidly tapering off Saturday night.