Boston — Tens of millions of residents along the East Coast are bracing for several centimeters of snow Sunday followed by dangerously cold temperatures that will take hold in much of the country from the Northern Plains to the tip of Maine. Winter storm warnings issued by the National Weather Service have already gone into effect for parts of the Mid-Atlantic through Monday morning, with the forecast projecting up to 15 centimeters of snow. Warnings will begin in New England on Sunday afternoon, with parts of Massachusetts, New Hampshire, Maine and Connecticut seeing as much as 25 centimeters of snow.