Winter storm warnings were issued from North Carolina to New Hampshire, with most areas expected to see 8 to 12 inches of snow and higher amounts possible in northern areas.
"It's the first of March, which, as you know, is the month that we say comes in like a lion and out like a lamb," New York City Mayor Michael Bloomberg said Sunday. "It's pretty clear that the lions are getting ready to roar."
The blizzard-like snow - together with sleet, freezing rain and wind gusts of up to 30 mph - contributed to four deaths on roads in Massachusetts, Rhode Island and on New York's Long Island.
More than 100 flights were scrubbed Sunday at Boston's Logan International Airport. Hundreds more flights were canceled at the New York region's three major airports, said Jennifer Friedberg, a spokeswoman for the Port Authority of New York and New Jersey.
More than 10 inches of snow was on the ground in New Jersey's Atlantic and Cumberland counties by 7 a.m. Monday, while South Carolina was dealing with 8 inches. Forecasters warned that the snow may temporarily stop for a few hours before starting up again by midmorning.
Nearly 335 flights scheduled to fly in or out of Newark Liberty International Airport had been canceled by Monday morning, and more cancellations were expected. In New Hampshire, Manchester-Boston Regional Airport listed about a dozen canceled arrivals Monday morning and close to 20 canceled departures.
Greyhound and Peter Pan bus lines canceled trips affecting travelers in and out of New York, Pennsylvania, Massachusetts and New Jersey.
Philadelphia declared a Code Blue weather emergency, which gives officials the power to go out onto the streets and bring in homeless people to shelters because the weather conditions pose a threat of serious harm or death.
New Jersey Gov. Jon S. Corzine said the storm could cost the state anywhere from about $2.5 million to $7 million, depending on its severity. So far, New Jersey has spent about $22 million on this winter's "frequent snow events," an amount that's about twice as much as what was budgeted for this year.
Those who had to be on the road Monday were told to allow extra travel time because streets were expected to be slick and slippery and visibilities were likely to be limited.
All New Jersey state offices will hold a two-hour delayed opening on Monday and the state Senate canceled all its scheduled committee meetings. Connecticut state employees were also given an extra 2 hours to get to work on storm-slick roads. South Carolina Gov. Mark Sanford delayed the opening of state offices in 28 counties in the central and northern parts of the state.
Dozens of schools across North Carolina, South Carolina and New Jersey also gave children a snow day. Public schools in Philadelphia, New York City and Boston did the same.
"We are urging residents to stay off the streets during the snowfall, if at all possible," Clarena I.W. Tolson, commissioner of Philadelphia's Streets Department.
New York City had 1,300 sanitation workers spreading salt and plowing streets Sunday night, and more than 2,500 were to be on duty on Monday, Bloomberg said. More than 100,000 tons of salt will be on hand.
It was likely to be the largest storm of the year, said city Sanitation Commissioner John Doherty, who warned that commuters should plan for complications.
"It's going to be a difficult morning for public transportation. We're going to be making every effort to have the roadways open," he said.
So far, the city's bus and subway service was running near normal with scattered delays on Monday morning, said NYC Transit spokesman Paul Fleuranges.
Forecasters said up to 10 inches could fall in parts of New York's Dutchess County, where eastern areas near the Connecticut border already had 8 inches by 7 a.m. Monday.
Duke Energy reported about 100,000 customers without electric service early Monday in North Carolina and another 78,000 in South Carolina. Progress Energy reported more than 5,300 customers lost service in North Carolina.
In Virginia, Dominion Virginia Power said nearly 114,000 customers were without power, with more than half in the Richmond metropolitan area. Appalachian Power, which serves southwest Virginia, reported about 5,600 outages.
Maryland has already spent more than $40 million responding to bad weather in what's been a colder-than-usual winter, Gov. Martin O'Malley said Sunday. Any money spent on digging out from the rare March storm will further burden a state that's facing a $2 billion budget shortfall.
"I don't like snow," O'Malley said.
Associated Press writers Daniel Yee and Christina Almeida in Atlanta; Rodrique Ngowi in Boston; and Samantha Henry in New Jersey contributed to this report.