"Travel will be very difficult to impossible, especially during the evening commute," in big Northeast cities on Wednesday, the National Weather Service said.
The big storm could blanket a large swath of the Eastern United States with a foot of snow and 60 mph wind gusts beginning on Tuesday and continuing Wednesday.
The winter storm — affecting about 49 million people from Tennessee through Maine — could bring a fresh round of power outages and treacherous travel.
Anger grew as utility crews struggled to restore service after the latest storm to wallop the Eastern Seaboard.
Commuters were facing delays Thursday morning as hundreds of flights were still grounded and more than 1 million utility customers remained without power.
The new storm has already caused thousands of canceled flights and could make roads treacherous in major cities, including Philadelphia, New York and Boston.
Authorities are planning for the worst, not knowing whether they will actually get it. The forecast for Boston predicts anywhere from zero to 12 inches of snow.
A swath of East Coast states was on edge Tuesday as an expected Nor'easter was rumbling toward the region, threatening 45 million people.
A second winter storm is forecast to hit the northeast after a powerful Nor'easter last week left nearly half a million people without power.
Residents have been without power for two days in some areas of the Northeast, with threes wiped out and homeowners surveying the flood damage. Another storm has been forecast for the coming week.