Rain and snow were already falling Sunday in parts of West Virginia and western New York and Pennsylvania with more wet, cold weather on tap over the next few days.
The National Weather Service posted a winter storm warning south of Buffalo where rain was expected to change over to snow overnight.
Pittsburgh was under a winter storm watch with as much as 6 inches possible in the metro area Sunday night.
"We have a low pressure system moving up the East Coast and that is going to give us the potential for snowfall," meteorologist Kristie Kubovic, KDKA-TV, Pittsburgh, said.
"This storm will ... return with some heavier precipitation on Monday," Kubovic added. "It looks to be a rain-snow mix at this point."
Although major snowfall was unlikely at lower elevations, forecasters warned the wet heavy flakes could make driving treacherous and cause tree limbs and power lines to snap.
"On the extreme end of possibilities with the storm, areas from the mountains of West Virginia northward to parts of southern Ontario and western Quebec could resemble a war zone with great carnage to forests, wooded neighborhoods and parklands," Accuweather.com meteorologist Andy Mussoline said in a Web site posting.
Weather.com said winter storms of such strength were unusual in the Northeast but not unprecedented. Heavy snow has fallen in the region as late as May.
Elsewhere Sunday, rain fell along the eastern seaboard and temperatures heated up into the 80s along the Mexican border