'Whiteout': Potentially historic winter storm closes in on Northeast TODAY's Al Roker says that a clipper system coming off the Great Lakes coupled with a storm system making its way up the East Coast will collide, causing historic and potentially dangerous weather conditions for the Northeast. By John Newland and Erin McClam, NBC News Updated at 10:38 a.m. ET: With more than 50 million Americans in its path and Boston in the crosshairs, a dangerous winter storm churned Friday into the Northeast, where thousands of schools were closed and thousands of flights canceled as forecasters warned of a whiteout. The National Weather Service put a swath of the country from New Jersey to Maine under a blizzard warning. For Boston, the storm threatened to be the worst since records were established in the 19th century. The biggest snowstorm to hit that city dumped 27.5 inches in 2003, and forecasters said this blizzard could beat that. The Weather Channel called for as much as 2 feet of snow in Hartford, Conn., and as much as 15 inches in New York. New Jersey readied 2,000 plows and salt trucks, Rhode Island police asked people for loaner snowmobiles, and out-of-state utility crews headed for Connecticut to help. Full coverage from The Weather Channel Watch live video of the Northeast blizzard "It's going to be crippling," said Jim Cantore, a meteorologist for The Weather Channel. Airline cancellations piled up all morning. More than 2,900 flights were scrapped for Friday and more than 850 for Saturday, according to FlightAware.com. At the major airports in New York and New England, most major airlines said they would shut down Friday afternoon. For people in the blizzard's path, forecasters and authorities had a clear message: Stay home. Schools were closed in Boston and for most of New England. Massachusetts Gov. Deval Patrick ordered non-essential state workers to stay home Friday and encouraged private employers to do the same. He said the snow would be "swift, heavy and dangerous." Boston planned to shut its subway system at 3:30 p.m. Snowplows sit parked at a New York Department of Sanitation depot as snow begins to swirl in Brooklyn, N.Y. In New York, where snow was falling by 7 a.m., the transit agency added more than 20 afternoon trains on its Metro-North commuter line from Grand Central Terminal to get people out of the city before the worst hit. Mayor Michael Bloomberg warned people to stay in and to use public transportation if they had to go out, although even that carried the possibility of disruptions. The city had 250,000 tons of salt at the ready for the roads. "This is a very serious storm, and we should treat it that way," said Tom Prendergast, president of the agency that runs New York subways and buses. NBCNewYork.com said there were already lines of up to 40 cars at some gas stations. The weather service warned that the storm would be accompanied by winds almost as powerful as those packed by a hurricane. "Visibilities will become poor, with whiteout conditions at times," the weather service said in an advisory issued Friday morning for the Boston area. Those venturing outdoors may become lost or disoriented. Justin Lane / EPA Worker Jimmy White attaches chains to tires at a New York City Department of Sanitation facility Thursday in preparation for the major winter storm expected to hit Friday. The winter storm gathered strength as two weather systems - a so-called clipper pattern sweeping across the Midwest and a band of rain from the South - began to converge over the Northeast. The Weather Channel said that snow would be heavy at times Friday in New York state, parts of Pennsylvania and most of New England. By Friday night, forecasters called for snow falling at 2 to 3 inches per hour in New England. Heavy, wind-driven snow was expected to coat New England on Saturday and shift to the New England coast by Saturday afternoon, the network said. Snow was finally expected to taper off in Boston by Saturday night and pull off the Maine coast by Sunday morning. Amtrak said it would cancel train service between New York and Boston on Friday, with the last northbound train leaving New York just after 1 p.m. and the last southbound train leaving Boston at 1:40. Those living on north- and east-facing shorelines from Boston south to Cape Cod Bay were told to prepare for tides 2 to 4 feet above normal. Flooding and beach erosion were dangers, and the weather service warned of widespread coastal flooding from Boston northward. "This one doesn't come along every day," said Alan Dunham, a meteorologist for the weather service. Show us your snow storm photos by adding #NBCNewsPics to your tweet or Instagram post, or upload your pictures directly by clicking the box below.