A blizzard of possibly historic proportions is set to strike the Northeast, starting today and bringing up to 2 feet of snow and strong winds that could shut down densely populated cities such as Boston and New York City.
A storm from the west will join forces with one from the south to form a nor'easter that will sit and spin just off the East Coast, affecting more than 43 million Americans. Wind gusts will reach 50 to 60 mph from Philadelphia to Boston.
"[It] could definitely be a historic winter storm for the Northeast," Adrienne Leptich of the National Weather Service in Upton, N.Y., said. "We're looking at very strong wind and heavy snow and we're also looking for some coastal flooding."
The snow began falling in New York City shortly before 7 a.m. ET. The snow is expected to mix with some sleet and then turn back into snow after 3 p.m.
Airlines have started shutting down operations between 2 p.m. and 5 p.m. at major airports in the New York area as well as in Boston, Portland, Maine, Providence, and other Northeastern airports. More than 4,000 flights have been cancelled on Friday and Saturday, according to FlightAware. Airlines hope to resume flights by Saturday afternoon.
New York City is expecting up to 14 inches, which is expected to start this morning with the heaviest amounts falling at night and into Saturday. Wind gusts of 55 mph are expected in New York City and Cape Cod, Mass., could possibly see 75 mph gusts.
Boston, Providence, R.I., Hartford, Conn., and other New England cities canceled school today. Boston and other parts of New England could see more than 2 feet of snow by Saturday.
Massachusetts Governor Deval Patrick declared a state of emergency Friday afternoon and announced a ban on all traffic from roads after 4 p.m. It is believed that the last time the state enacted such a ban was during the blizzard of 1978.
Beach erosion and coastal flooding is possible from New Jersey to Long Island, N.Y., and into New England coastal areas. Some waves off the coast could reach more than 20 feet.
"Stay off the streets of our city. Basically, stay home," Boston Mayor Tom Menino warned Thursday.
Blizzard warnings were posted for parts of New Jersey and New York's Long Island, as well as portions of Massachusetts, Rhode Island and Connecticut, including Hartford, New Haven, Conn., and Providence. The warnings extended into New Hampshire and Maine.
To the south, Philadelphia was looking at a possible 4 to 6 inches of snow.
Thousands of flights have already been canceled in anticipation of the storm. Amtrak said its Northeast trains will stop running this afternoon.
Bruce Sullivan of the National Weather Service says travel conditions will deteriorate fairly rapidly Friday night.
"The real concern here is there's going to be a lot of strong winds with this system and it's going to cause considerable blowing and drifting of snow," he said.
Parts of New York, still reeling from October's Superstorm Sandy, are still using tents and are worried how they will deal with the nor'easter.
"Hopefully, we can supply them with enough hot food to get them through before the storm starts," Staten Island hub coordinator Donna Graziano said.
New York City Mayor Michael Bloomberg said plows and 250,000 tons of salt were being put on standby.
"We hope forecasts are exaggerating the amount of snow, but you never can tell," Bloomberg said Thursday.
Residents of the Northeast have already begun to hit stores for groceries and tools to fight the mounting snow totals.
The fire department was called in to a grocery store in Salem, Mass., because there were too many people in the store Thursday afternoon trying to load up their carts with essential items.
"I'm going to try this roof melt stuff for the first time," Ian Watson of Belmont, Mass., said. "Just to prevent the ice dam. ... It's going be ugly on that roof."
ABC News' Max Golembo and The Associated Press contributed to this report.