Snow tapers off but Northeast still dealing with cold, icy streets

"Stay away from the coasts," the National Weather Service in Boston tweeted.

On Thursday afternoon, the tide gauge at Boston Harbor matched its record at 15.1 feet -- previously set during the blizzard of 1978.

Video from a resident of Hull, just to the southeast of Boston, showed the icy mess inundating one street with water above the wheel wells of cars and coming up to the doors of homes.

Latest developments

• Fast-moving weather: The storm was moving quickly and, fortunately, the center of the system and its highest winds stayed offshore, CNN meteorologist Tom Sater said,

• Snow slows: Forecasters at the National Weather Service said snowfall amounts will diminish in southern New England, but wind and cold temperatures will be threats on Friday.

• Deadly conditions: At least 16 people have died this week due to severe weather, officials said. Six deaths were reported in Wisconsin, four in Texas, three in North Carolina, and one each in Michigan, Missouri and North Dakota.

• Going dark -- with no heat: More than 46,000 customers don't have power on the East Coast, according to utility companies in five states.

• Stay home: Boston Mayor Marty Walsh told residents too many people were getting their cars stuck. "We want to clear the streets."

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Roads fill with water

The bomb cyclone, which developed overnight, occurs when a low-pressure system has a significant, rapid drop in atmospheric pressure.

In Quincy, Massachusetts, one street turned into an icy river.

More than 4,300 US flights were canceled for Thursday, according to Flightaware.com. New York's LaGuardia airport reopened later in the day, and JFK International was expected to follow suit. Passengers were urged to check with airlines on flight information.

Hundreds of East Coast schools were closed and grocery store shelves were emptied.

"This storm is intense!" the NWS Boston office tweeted. "Expect the unexpected."

Governor: Power won't be fixed in extreme winds

In Connecticut, Gov. Dan Malloy urged residents to stay off roads. The forecast calls for a minimum of 6 inches of snow and winds as strong as 50 mph, potentially hindering utility repairs should power lines go down.

"We cannot and will not order people up in trucks to fix lines when the winds are too high," Malloy said.

At an evening news conference, the governor said third-shift state employees should go to work Thursday night after the worst of the storm passed.

Virginia Gov. Terry McAuliffe declared a state of emergency and urged residents to prepare for the storm, which could dump as much as a foot of snow in parts of eastern Virginia.

"With this forecast in mind, all Virginians should take the necessary precautions now to ensure they are prepared for the travel disruptions, power outages and other threats to health and safety that could arise during this significant weather event," McAuliffe said.

Record-breaking temperatures on the way

Dozens of cities are set to endure record-breaking cold, CNN meteorologist Brandon Miller said.

New York City and Philadelphia will plummet to 3 degrees this weekend. Boston will plunge to 7 degrees below zero -- plus up to a foot of snow.

Winds chills will be well below zero this weekend, with some areas feeling like it is minus 40.

How bomb cyclones work

Bomb cyclones often draw colder air in from the north, then blast out icy temperatures.

They frequently occur in North America, when cold air collides with warm air over the Atlantic Ocean -- though they've also been reported in eastern Asia and South America.

The bomb cyclone now blasting the Northeast actually doubled the rate necessary to earn it that classification.

It rapidly intensified overnight, undergoing bombogenesis -- or a pressure drop of 24 millibars in less than 24 hours.

This bomb cyclone dropped 53 millibars in just 21 hours, intensifying faster than any such occurrence in recent history.