BOSTON -- A major winter storm headed toward the U.S. Northeast on Thursday, with up to 0.6 metres of snow expected for a Boston-anchored region that has seen mostly bare ground this winter, the National Weather Service said.

It will be a rare and major storm, the type that means "you can't let your guard down," said Louis Uccellini, director of the weather agency's National Centers for Environmental Prediction.

"This has the potential for being a dangerous storm, especially for Massachusetts into northeast Connecticut and up into Maine," Uccellini said.

The snow will start Friday morning, with the heaviest amounts dumped that night and into Saturday, the National Weather Service said.

A coastal flooding watch was in effect for some shore communities in Massachusetts, Connecticut and New York's Long Island -- just outside New York City.

Tom Meyers, marketing director for Wachusett Mountain Ski Area in Massachusetts, said many participants at an annual conference of the National Ski Areas Association this week, were "buzzing" about the storm.