Northeasterners know the drill by now. The snowstorm that passed through late Wednesday night dropped over a foot of snow in many areas, grounding planes, and leaving more than 400,000 people without power in Washington, D.C. Public schools in Boston, New York City, Washington, D.C., and Philadelphia declared a snow day, as did non-emergency New York City government offices. Thousands of flights have also been canceled. Amtrak suspended service from New York to Boston and from New Haven to Springfield, while the Long Island Rail Road moved to a reduced schedule, and New York bus service was suspended. Central Park broke an 86-year-old record for January snowfall, with 19 inches falling before 6:30 a.m. Thursday. Parts of New Jersey also got 19 inches, while 17 inches fell in Philadelphia. In Washington, D.C., President Obama’s helicopter was grounded and he had to navigate snow-snarled traffic in his motorcade on his return from Andrews Air Force Base.