Officials in North Carolina link three deaths to the storm.
Gov. Roy Cooper of North Carolina said two men died when a pickup truck overturned in an icy creek in Moore County, and a third death has been reported in Beaufort County.
“We still don’t know the full effects at this time, but we do know that the winds out there have been ferocious,” Mr. Cooper said on Thursday, urging North Carolinians to stay home. High winds and low temperatures have kept crews from clearing many of the roads.
State troopers have received more than 1,000 calls since the storm started, more than 700 of which were related to car crashes.
Overnight, about 20,000 people in North Carolina were without power, but that number was down to about 6,500 by Thursday morning.
In Virginia, more than 40,000 homes and businesses were without power.
The Weather Service said cities along the Atlantic Ocean and the Chesapeake Bay could get about a foot of snow, and the Virginia Department of Transportation said more than 600 roads had been affected.
“Virginians should keep a close watch on the local weather forecast and stay off roads during this weather event unless travel is absolutely necessary,” the governor’s office said in a statement on Thursday, one day after Gov. Terry McAuliffe declared an emergency for the commonwealth.
The Port of Virginia was closed to inbound and outbound traffic, and rail and air services were canceled or delayed. The state said National Guard troops were on standby to help move emergency officials through deep snow in the Hampton Roads region, which includes Newport News, Norfolk and Virginia Beach and is home to more than 1.7 million people.
The area is not expected to inch above freezing temperatures until Sunday — and even then, the high will be only 33 degrees, according to the Weather Service.
Temperatures are expected to dip into the single digits on Thursday night, and wind chills could hit minus 7.
What exactly is a ‘bomb cyclone,’ or bombogenesis?
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; the formation of such a storm is called bombogenesis.
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.