BOSTON – A storm that forecasters warned could be a blizzard for the history books, with a potential for up to 3 feet of snow, clobbered the New York-to-Boston corridor on Friday, grounding flights, sending office workers home early and knocking out power to half a million customers across the Northeast.

By Friday night, more than 18.5 inches of snow had fallen in parts of central Connecticut, and more than 16 inches covered parts of Mansfield, Mass., a half-hour drive southwest of Boston. Throughout the Northeast, more than 500,000 homes and businesses lost electricity as wet, heavy snow, freezing rain and howling winds caused havoc.

Earlier, as meteorologists warned of the impending blizzard conditions, shoppers from New Jersey to Maine crowded into supermarkets and hardware stores to buy food, snow shovels, flashlights and generators, something that became a precious commodity after Superstorm Sandy in October. Others gassed up their cars, another lesson learned all too well after Sandy. Across much of New England, schools closed well ahead of the first snowflakes.