Bomb Cyclone’ Swirls Northward, Bringing Snow and Bitter Cold

Bitter cold, strong winds and blizzards were expected to hit the Mid-Atlantic States and the Northeast as a powerful winter storm that brought ice, sleet and snow to the Southeast curled northward on Thursday.

• The storm, which some meteorologists classified as a “bomb cyclone” for its sharp drop in atmospheric pressure, forced flight cancellations and school closings up and down the East Coast.

• New York City was forecast to receive five to eight inches of snowfall, although Queens and neighboring Nassau County could get up to 10 inches, forecasters said.

• The National Weather Service issued blizzard warnings for parts of the Eastern Seaboard from North Carolina to Maine, with travel “very dangerous to impossible” in the highly populated Hampton Roads region of Virginia, which could receive up to 12 inches of snow in places.

• New England is expected to be hit particularly hard, with blizzard conditions beginning on Thursday in parts of Maine, Massachusetts and Rhode Island, according to forecasters.
The new round of shivering prolonged what has already been a difficult period in emergency rooms across a broad swath of the United States. In the Atlanta area, where temperatures were hovering around freezing on Wednesday but were expected to plunge into the teens after nightfall, doctors said they had been seeing an unusual number of patients with weather-related emergencies.

“This is the most challenging winter, in terms of exposure, that I’ve ever seen,” said Dr. Brooks Moore, the assistant medical director of the emergency department at Grady Memorial Hospital, Atlanta’s public hospital.

Dr. Moore said that about 20 people were arriving at the emergency room each day with minor complaints related to the weather and that about the same number were appearing with conditions like asthma or emphysema that were exacerbated by the cold.

He added that doctors were seeing about one or two patients a day whose core body temperatures had fallen into the low 80s — normal is about 98.6 degrees — and required “aggressive rewarming” techniques.

What exactly is a ‘bomb cyclone’?

When discussing the storm, some weather forecasters have referred to a “bomb cyclone.” Calling it a bomb sounds dire, but such storms are not exceedingly rare — there was one in New England recently.

What makes a storm a bomb is how fast the atmospheric pressure falls; falling atmospheric pressure is a characteristic of all storms. By definition, the barometric pressure must drop by at least 24 millibars in 24 hours for a storm to be called a bomb cyclone.

Here is how it works: Deep drops in barometric pressure occur when a region of warm air meets one of cold air. The air starts to move, and the rotation of the Earth creates a cyclonic effect. The direction is counterclockwise in the Northern Hemisphere (when viewed from above), leading to winds that come out of the northeast — a Nor’easter.

That’s what happened at the end of October, when warm air from the remnants of a tropical cyclone over the Atlantic collided with a cold front coming from the Midwest. Among other effects then, more than 80,000 customers in Maine lost power as high winds toppled trees.

A similar effect was occurring Wednesday, as warm air over the ocean met extremely cold polar air that had descended over the East. Pressure was expected to fall quickly from Florida northward.