Update: 5:15 am: (AP) Early Tuesday, forecasters downgraded expected snowfall numbers, saying New England would fare the worst, but even then not as bad as expected.

Bruce Sullivan of the National Weather Service said Philadelphia and central New Jersey could see about 6 inches. Boston and Providence, Rhode Island, could get the most snow, about 2 feet, Sullivan said. New York could see 10 inches to 20 inches, and Hartford, Connecticut, 1 to 2 feet.

Earlier story below:

Faced with the threat of the region being buried in snow from a nor'easter making its way up the coast, the governors of Pennsylvania and New Jersey declared emergencies, a major airline suspended all its flights in and out of Philadelphia, and NJ Transit announced it would halt all bus and train operations.

All Philadelphia municipal offices will be closed Tuesday, as will city public and archdiocesan schools, Mayor Nutter said Monday at a late-night news conference at the city's emergency operations center.

Despite changing forecasts, he said, the city is still expecting 6 to 10 inches of snow, with gusty winds.

Trash and recycling will not be collected Tuesday, Nutter said. And he urged residents to offer snow-removal help to neighbors and to bring all pets inside during the storm and severe cold.

All nonemergency travel was banned in New Jersey starting at 11 p.m. Monday.

At a Pennsylvania Department of Transportation news conference Monday night, John Krafczyk, maintenance manager for the five-county Philadelphia region, implored people to stay off the roads.

"If you don't absolutely have to go somewhere, please stay home," Krafczyk said. "If you must travel, be sure to leave plenty of room between you and the vehicles around you - at least six car lengths. And please slow down.

"Whiteout conditions can come up on you quickly, and you won't be able to see what's in front of you or behind you."

Officials at SEPTA said the Market-Frankford Line and Broad Street subways would operate all night in place of bus service. Regional Rail is expected to run on a Saturday schedule on Tuesday.

Pennsylvania Gov. Wolf signed a disaster emergency proclamation authorizing state agencies to use all available resources and personnel to deal with major problems and waiving bidding for emergency contracts.

In New Jersey, where part of the Shore and northeastern parts of the state are expected to experience blizzard conditions, Gov. Christie also declared a state of emergency and ordered government offices to close early Monday and all day Tuesday.

NJ Transit said it would shut down all rail and bus operations at 8 p.m. Train service will not resume until Thursday while buses and light rail could be running again Wednesday.

US Airways, the largest airline at Philadelphia International Airport, suspended its flights at Philadelphia, Boston, and the New York metropolitan area's three major airports. Most scheduled Tuesday flights at the airport have been canceled.

Mayor Nutter declared a snow emergency starting at 6 p.m., banning parking from designated snow routes. He also reminded residents of new law that imposes fines for leaving cats and dogs outside in winter storms.

Current forecasts call for light snow before the main part of the storm hits later tonight.

The National Weather Service is calling for substantial accumulations throughout most of the region, and more close to the Shore, by the time the storm ends Tuesday. In his forecast, John Bolaris takes a more conservative outlook and puts the accumulation total at 4 to 6 inches.

Winds on Tuesday could gust to 30 m.p.h.

The weather service did not include Chester County in its winter-storm warning, and the zone of heavy snow will have a sharp western cutoff, said Louis W. Uccellini, one of the nation's leading storm experts and the weather service director.

Just before noon, he said, the clipper that has generated light snows was falling apart, and the main coast storm was deepening off the North Carolina/Virginia coast, as forecast.

However, forecasters still didn't have a handle on precisely where the bands of heaviest snow would set up and just how far west the snows would fall.

Accumulations could be less everywhere in the region if the storm tracks farther out to sea.

The NWS is advising that all travel be postponed between 7 p.m. Monday and 9 a.m. Tuesday.

A winter storm warning is in effect until 6 p.m. Tuesday for most of the region, except for Chester County, where a lower level winter storm advisory will be in place.

A blizzard warning has been issued for Ocean and Monmouth Counties and points north, including New York City.

A full travel ban was set to go into effect on all New York City-area roadways at 11 p.m., the Associated Press reported. Only emergency workers will be allowed on streets in 13 counties, including Long Island and all of New York City; anyone caught violating the ban could be issued a $300 summons.

Here's the latest of what you need to know:

PHILADELPHIA INTERNATIONAL AIRPORT

American Airlines and merger partner US Airways, Philadelphia's dominant airline, suspended flights late Monday afternoon at Philadelphia, Newark, N.J., New York's LaGuardia and JFK airports and Boston Logan airport.

Tuesday operations will be "very limited in the Northeast for American, US Airways and all regional partners," said American spokeswoman Andrea Huguely. "We plan to resume operations as soon as it is safe to do so." American canceled 626 flights systemwide Monday and 970 are canceled Tuesday.

At Philadelphia International Airport, American and US Airways canceled 356 flights Monday "and preliminary numbers indicate we will have approximately 500 canceled flights on Tuesday," said airline spokeswoman Victoria Lupica.

Altogether more than 430 flights to or from Philadelphia International scheduled for Monday were canceled, according to FlightAware.com.

DRIVING

Mayor Nutter declared a snow emergency starting at 6 p.m. banning parking on designated snow emergency routes. The Philadelphia Parking Authority said it would offer a flat 24-hour rate of $5 due to the snow emergency. The special rate is in effect through 8 a.m. Wednesday at seven PPA-operated lots in the city. The PPA said meter and time violations wouldn't be enforced until the emergency was lifted, but it would begin ticketing and towing vehicles parked on snow emergency routes at 6 p.m. Monday. Go to www.philapark.org for the $5 parking locations.

Surrounding towns have declared similar emergencies.

A number of accidents are being reported around the area, perhaps due to slippery road surfaces. Motorists are advised to reduce speed and driver carefully.

Speed restrictions are in place on the Walt Whitman, Commodore Barry, Ben Franklin, and Betsy Ross Bridges, with a limit of 35 m.p.h.

Speed limits also have been reduced to 45 m.p.h. on the Garden State Parkway and the New Jersey Turnpike.

MASS TRANSIT

SEPTA: Due to the storm, there will be no OWL Bus service. Market Frankford and Broad Street Line service will operate all-night. Regional Rail is expected to operate on a Saturday schedule on Tuesday. www.septa.org

PATCO: Will operate trains every 10 minutes during morning and afternoon rush hours on Tuesday and every 15 minutes during nonpeak times.

NJ Transit: Is shutting down all bus and rail operations at 8 p.m. Trains, bus, and light rail service will resume "when conditions permit," the agency said. www.njtransit.com

Amtrak: The agency will not run trains on the Northeast Corridor between New York City and Boston.

Acela Express and Northeast Regional trains between New York and Washington, and Keystone Service connecting Harrisburg, Philadelphia and New York, will operate "at reduced frequencies," Amtrak said. www.amtrak.com

GOVERNMENT

Philadelphia government offices and courts closed at 2 p.m. and will be closed Tuesday.

New Jersey government offices closed at 1 p.m. and will be closed Tuesday for nonessential employees.

Delaware County will open two hours late on Tuesday, at 10 a.m.

West Deptford Municipal Court has canceled its session scheduled for Tuesday.

The New Jersey State Assembly canceled Monday's session.

SCHOOLS

Many school districts closed early Monday, including Philadelphia public and parochial schools, which will remain closed Tuesday.

Temple University has canceled night classes, beginning at 4:45 p.m.

Community College of Philadelphia closed at 2 p.m. today and will be closed Tuesday.

All New Jersey public colleges and universities will be closed Tuesday.

Inquirer staff writers Jessica Parks, Susan Snyder, Justine McDaniel, Anthony R. Wood, Paul Nussbaum, Linda Loyd, Robert Moran, and Mari A. Schaefer contributed to this article.