So far, more than 7,600 US flights have been canceled and thousands of schools have closed due to what could be a historic storm. Winter storm warnings and watches have been hoisted over a region stretching from North Virginia into Maine.
Local and state authorities warned residents to be prepared and to avoid unnecessary travel as winds in some areas could reach up to 50 to 60 mph, reducing visibility to zero.
"We're talking one in every three people in the US are dealing with significant snow in the forecast in the next several hours," said CNN meteorologist Pedram Javaheri.
Major cities including New York and Boston could get deluged with snow if the storm hugs the coastline, but they could see significantly less snow if the storm shifts closer to land.
Weather models on early Tuesday showed that the heaviest snow, as much as two feet, could hit areas west of New York such as Scranton and Allentown, Pennsylvania.
Among major developments:
— Snow is falling in Washington DC up through Philadelphia, and New York City as of Tuesday morning.
— 31 million people are under a blizzard warning, 31 million are under a winter storm warning and 9 million are under a winter weather advisory.
— The heaviest snow is expected to hit between 6 a.m. and 9 a.m. and could turn into sleet later, according to the CNN Weather Center.
— Boston, Baltimore, Philadelphia and New York City school districts will be closed Tuesday along with many government offices.
— Airlines canceled over 7,600 US flights scheduled for Monday, Tuesday and Wednesday, according to Flightaware.com.
— New York City could get up to 20 inches of snow, Mayor Bill de Blasio said, with coastal flooding and wind gusts as high as 40 to 50 mph also forecast. But with warmer air filtering into the area, weather models predict that snowfall could be somewhere around 10 to 14 inches.
— State of emergencies have been declared in Maryland, Virginia, New York, New Jersey and Pennsylvania.
— Philadelphia could see 10 inches of snow, causing dangerous travel conditions and wind gusts up to 55 mph in many areas.
— Parts of Massachusetts could see 24 inches or more and similarly powerful winds, said Gov. Charlie Baker. Coastal areas could see hurricane-force wind gusts and a storm surge as high as two to three feet is also possible. Boston could see as much as 12 inches of snow for the metro region.
— In Connecticut, a statewide travel ban was scheduled to go into effect Tuesday at 5 a.m. "Wherever you are at sunrise Tuesday morning, expect to remain there throughout the remainder of the storm and into (Tuesday) night," said Connecticut Gov. Dannel Malloy.
— In Virginia, the Coast Guard closed the Port of Virginia on the harbor at Hampton Roads. In a news release Monday night, the agency said 50 mph winds predicted from the pending storm could create hazardous conditions that would make it difficult for Coast Guard units to reach any distressed mariners.
Travel warnings, snow and sleet
Warnings to use caution came from public officials up and down the East Coast — including the President.
"Everyone along the east coast be safe and listen to local officials as a major winter storm approaches," President Donald Trump tweeted.
Federal agencies in the Washington area will open three hours late, with employees having the option of taking unscheduled leave or teleworking, according to a press release from the U.S. Office of Personnel Management.
This storm system already hit the Midwest, claiming two lives in Wisconsin. According to the Milwaukee County Medical Examiner's office, the victims — both men — died in separate weather-related activities. One man, 76, was operating a snow blower before he died; the second man, 64, was shoveling snow, said investigator Jenni Penn. They were both cardiac-related deaths, Penn said.
In addition to the hazards produced by a deluge of snow, the region also is expecting downed power lines and service interruptions.
"This should be a very serious blizzard, one that everyone should take seriously," New York's de Blasio said.
The period of greatest accumulation of snow should be between 6 a.m. and noon Tuesday, with a possible 2 to 4 inches per hour and whiteout potential during that time, de Blasio said.
In Massachusetts, its governor said the state expects sleet, rain and extremely cold temperatures along the coast.
"This is going to be a lot of snow and it's going to be a mess," Baker said.
A snow emergency is expected to go into effect in Boston at 7 a.m. Tuesday, Boston mayor Walsh said.