A springtime nor’easter is barreling into storm-strained New England, threatening coastal flooding, up to a foot of snow in some areas and high-wind conditions that could trigger another round of widespread power outages.The deepest snow is expected to fall in Plymouth, where 8 to 12 inches is forecast. Boston should see 6 to 8 inches, with the slim possibility of up to a foot, according to the National Weather Service, which issued a winter storm warning until 8 a.m.