The snow fall totals are being measured in inches for now, but forecasters say the final totals are likely to be in feet as a major winter storm hits the Northeast.

More than 35 million people along the Philadelphia-to-Boston corridor rushed to get home today as governors in the affected states took pre-emptive action, ordering roads to be closed to all but emergency vehicles and asking residents to stay out of the streets.

FlightAware.com says more than 6,700 U.S. flights through Tuesday have already been scrubbed and another 2,000 have been delayed. And the cancelations and delays are expected spill over into Wednesday, if not longer.

Travelers at Tampa International Airport are being impacted as well.

As of 9 p.m., the airport had 38 canceled flights (arrivals and departures) and 69 delays. Most of the flights are to and from the New York/New Jersey airports, Philadelphia and Boston. The average delay is now about 52 minutes.

Airport officials are urging all travelers to check with their airlines before coming to the airport and to reschedule flights if necessary.

A blizzard warning was issued for a 250-mile stretch of the Northeast, including New York and Boston. The National Weather Service is even using terms like "life-threatening" and "historic."

Government officials began to activate emergency centers on Sunday, as professional sports teams, schools and utilities hastily revised their schedules and made preparations.

"This could be a storm the likes of which we have never seen before," New York City Mayor Bill de Blasio said at a news conference in a Manhattan sanitation garage, where workers were preparing plows and salt for the massive cleanup of about 6,000 miles of city roadways.

In Massachusetts, Gov. Charlie Baker warned residents to prepare for roads that are "very hard, if not impossible, to navigate," power outages and possibly even a lack of public transportation.

Boston is expected to get 18 to 24 inches of snow, with up to 2 feet or more west of the city, and Philadelphia could see up to a foot, the weather service said.

The Washington area expected only a couple of inches, with steadily increasing amounts as the storm heads north.

Wind gusts of 75 mph or more are possible for coastal areas of Massachusetts, and up to 50 mph further inland.

Airlines prepared to shut down operations along the East Coast, and that was expected to lead to the cancellation of about 1,700 flights, according to the flight tracking site FlightAware.

What you need to know

The busy Northeast corridor has prepared for a winter wallop that was expected to bring up to 2 feet of snow from northern New Jersey all the way up to Massachusetts. If you're traveling to the Northeast or have loved ones there, here's what you need to know about the coming storm:

Snowstorm vs. Blizzard: What's the Difference?

The National Weather Service issued a blizzard warning for a huge swath of the region, meaning potential white-out conditions as heavy snow swirls amid gusting wind. The weather service says a blizzard includes sustained or frequent wind gusts of 35 mph or greater and considerable falling snow that lasts for at least three hours. This storm is expected to last up to 36 hours in some locations, forecasters said.

Air Travel

Airlines had cancelled about 2,000 flights Monday because of the storm and were expected to cancel more, according to the flight tracking site FlightAware. Those affected most are the three airports serving New York City. More than 20 percent of flights in Boston and Philadelphia we cancelled.

On the Rails

Amtrak was operating a normal schedule Monday, but said it would re-evaluate as conditions warrant. It said announcements about service changes would be made as far in advance as possible, but it also encouraged passengers to watch the weather closely.

New York

Up to 2 feet of snow was predicted, with the heaviest snow falling from about midnight Monday through Tuesday afternoon. Winds will be strongest across eastern Long Island. About half the flights Monday at the region's three major airports were cancelled.

Boston

A blizzard warning will be in effect from 7 p.m. Monday to 1 a.m. Wednesday, with about 20 to 30 inches of snow forecast for the city and its suburbs. Near-hurricane force winds were predicted for Cape Cod and the nearby islands.

Hartford, Connecticut

From 20 to 30 inches of snow was predicted, including snowfall rates of 2 to 4 inches per hour at some points Monday night or Tuesday morning.

Providence, Rhode Island

Accumulations of around 20 to 30 inches were expected with locally higher amounts possible, plus blizzard conditions that include damaging winds and considerable drifting and blowing snow.

Philadelphia

Snow was falling Monday morning, but the storm was expected to being in earnest later Monday. About a foot of snow was expected before the storm ends about 6 p.m. Tuesday, with less to the west and more in New Jersey toward the coast.

Washington–Baltimore

Snow was expected end by midday Tuesday, with about 1 to 2 inches accumulating in Washington and 2 to 5 inches in Baltimore.

A storm system driving out of the Midwest brought several inches of snow to Ohio on Sunday. A new low pressure system was expected to form off the Carolina coast and ultimately spread from the nation's capital to Maine.

Information from the Associated Press was used in this report.