Richard Perry/The New York Times
In Jersey City, Jose Angelo, left, helped Isauro Palacios, a contractor from Belleville, N.J., as he loaded a new snow blower into the back of his truck Thursday as a snowstorm approached the region.
As a major winter storm made its way up the Atlantic Coast on Thursday, local authorities from New York City to Maine began to make preparations for what forecasters said could be the heaviest snowfall for some cities in the Northeast in a century.
Airlines began announcing the suspension of flights out of New York and Boston airports starting Friday night, as thousands of workers readied their plows, checked their stocks of salt and braced for what will most likely be a cold, wet weekend. Amtrak announced that it would suspend northbound service out of Penn Station in New York and southbound service out of Boston beginning early Friday afternoon.
Gas stations in parts of New York City and New Jersey had long lines Thursday night, according to local residents, a signal, perhaps, that many were taking storm warnings seriously.
More than 2200 flights for Friday had been cancelled, according to the Web site FlightAware, the majority originiting or departing from the areas affected by the storm.
By late Thursday night, schools across New York and Connecticut had announced they would close, or dismiss students early.
On Long Island, where some forecasts said there could be more than 18 inches of snow, the power company, which has received heavy criticism for its response to Hurricane Sandy, promised customers that they were prepared.
The city of Boston, where forecasts called for more than two feet of snow to fall by Saturday, announced that it would close all schools on Friday, joining other localities in trying to get ahead of the storm and keep people off the roads.
“We are taking this storm very seriously and you should take this storm very seriously,” said Jerome Hauer, the New York State Commissioner of the Division of Homeland Security and Emergency Services, at an afternoon news conference.
“If you don’t have to go to work tomorrow, we suggest that you do not,” he said. “If you do, we suggest that you plan for an early departure.”
The latest forecasts, he said, called for between 12 and 20 inches of snow in the New York City region and wind gusts that could exceed 60 miles per hour.
However, with the storm still some distance away, forecasters warned that predictions could change. The first sign of the storm will be a dusting of light snow that is expected to start falling across the region Friday morning.
At some point Friday night, the arctic jet stream will drop down from Canada and intersect with the polar jet stream, which usually travels through the lower 48 states.
“They will cross somewhere between New Jersey and Nantucket,” said Tim Morrin, a meteorologist at the National Weather Service. “That is where the center of the storm will deepen and explosively develop.”
If the current models hold, the storm could rival the blizzard of 1978 in New England, when more than 27 inches of snow fell in Boston and surrounding cities. That storm, which occurred on a weekday, resulted in dozens of deaths and crippled the region for days.
Peter Judge, a spokesman for the Massachusetts Emergency Management Agency, said more than 20 agencies had gathered at the agency’s operations center in Framingham, Mass., where they were preparing for a historic storm.
“From our perspective, this is a very severe, blizzard-type storm that we haven’t had for quite a long time,” Mr. Judge said. “Worst-case scenario, this will be the worst one that we’ve dealt with in many, many years. I can’t even come up with something comparable.”
Officials prepared for debris management, snow removal and supplies distribution, he said, as well as widespread power failures, which he said were the major concern. “People will lose their heat when they lose their power, and they’re certainly much more in harm’s way than at other times of the year,” he said.
Boston was bracing for the worst of the storm to hit between 2 and 5 p.m. Friday. Gov. Deval Patrick, who called the pending storm “a serious weather event,” has ordered all nonemergency personnel to work from home Friday and encouraged private employers to keep their workers home.
Governor Patrick asked that all vehicles stay off the roads after noon on Friday and said the Massachusetts Bay Transit Authority, including all subway, buses and commuter rail services, would close at 3:30. He said mass transit was being kept open until 3:30 to allow the first shift of emergency and hospital workers to get home and the second shift to get to work.
Boston public schools will be shut, and the governor encouraged all other school districts in the state to cancel classes.
The state is preparing “warming centers” to be open in local communities in case of major power failures and will move people into larger regional centers if they need to stay overnight.
At Logan Airport in Boston, long lines were forming by midafternoon as people tried to flee the storm.
“You don’t know what’s going to happen,” said Martin Stewart, 50, a service technician standing in a lengthy line at the airport. He had moved up his trip to Scotland to make sure he could get out. “Why mess around?” he said.
Two women waiting in line said they were leaving for London as planned but were somewhat wistful about missing a big storm. “We love the snow,” said Lynne Fistori, 36, who is taking a quick trip with her sister-in-law, Laura Fistori, 36. They expect that the men and children whom they are leaving behind will just ration their food and play in the snow.
The eastern-facing coastline — including cities like Scituate, south of Boston, and the Cape Ann area north of Boston — is at risk for major flooding, which could bring “a lot of beach erosion, potential damage of homes along the coast,” Mr. Judge said.
For the past 48 hours, weather predictions for the region have varied wildly, with forecasts calling for something more than a dusting to a car-burying snowfall.
But by Thursday, Mr. Morrin said, there was “enough evidence right now to say the legacy of this storm will be widespread.”
Just what parts of the New York City metropolitan area will be hit hardest will become clearer as the low-pressure system moves north, but Mr. Morrin said that all the forecasting patterns put the storm on “a historically favorable track.”
The morning commute on Friday could be affected by light snowfall. Temperatures are expected to rise during the day, which could mean a snowy, rainy mix — or just rain, Mr. Morrin said.
However, by Friday night, temperatures are expected to drop precipitously as cold air from the north moves down, turning the precipitation into snow.
“When the door opens, it is going to open wide,” Mr. Morrin said.
For New Yorkers, that could mean that the slushy mess from the daytime could freeze, not only creating hazardous conditions on the roads but also weighing down tree branches and power lines.
Michael Clendenin, a spokesman for Consolidated Edison, said the utility was making preparations for the storm and would have extra crews available to deal with any problems.
Mayor Michael R. Bloomberg met Thursday with New York sanitation workers who were preparing for the storm.
“The good news, I guess, if you like snow, is that we’re going to have snow,” Mr. Bloomberg said.
“The better news is that if it’s going to happen, having it happen overnight Friday into Saturday is probably as good timing as we can have,” he added, “because the Sanitation Department then has the advantage of being able to clean the streets when there’s normally less traffic.”
New York State canceled all Civil Service examinations scheduled for Saturday.
Mr. Hauer said that coastal areas of Queens, Brooklyn and Long Island could see flooding and should be prepared to seek alternative shelter. While the storm surge is only expected to be 3 to 5 feet — well below the 14-foot surge that Hurricane Sandy delivered — he said large waves could bring water inland.
“If you see flooding, have plans for somewhere to go,” he said.
As the storm moves north, the heaviest bands of snow and rain would tend to occur northeast of the storm’s center.
“A lot depends on where the heaviest bands of snow develop,” he said. “If a band sits over an area, you can get three inches of snow an hour.”
By Friday morning, he said, it will be clearer where the worst of the storm is likely to hit.
Marc Santora reported from New York. Jess Bidgood and Katharine Q. Seelye contributed reporting from Boston.
This article has been revised to reflect the following correction:
Correction: February 7, 2013
An earlier version of a picture caption with this article misidentified the occupation of Jose Angelo. He is an employee of Isauro Palacios, a contractor. He is not a hardware store employee.
A version of this article appeared in print on February 8, 2013, on page A19 of the National edition.