The second winter storm in a week hit New York and surrounding states on Wednesday, bringing heavy snow that delayed or cancelled flights and snarled traffic at evening rush hour as thousands remained without power from the last northeaster.
Between 20 and 30cm of wet, heavy snow, some of it accompanied by thunder and lightning, were forecast for New York City and surrounding New Jersey and Connecticut suburbs through Thursday morning.
Wind gusts could create "near-whiteout conditions" for commuters, the National Weather Service said.
Some workers were stranded with both buses and trains cancelled.
Up to 60cm of snow was expected in some inland parts of New Jersey, New York, Connecticut and Massachusetts and 46cm was possible in Maine.
The storm will spread with varying degrees of intensity across the Northeast, from western Pennsylvania up into New England, the weather service said.
Around half of all scheduled flights were cancelled at the three major airports serving New York City, according to the tracking service FlightAware.
The website said more than 2100 flights had been delayed and 2700 cancelled, most of them in the Northeast, as of 8pm local time.
All schools were closed in Philadelphia, while other schools across the region cancelled classes or shortened the school day ahead of the storm, local news media reported.
Connecticut Governor Dannel Malloy ordered many state workers to head home early on Wednesday afternoon at staggered intervals to avoid traffic snarls on slippery roads.
Last week's storm brought major coastal flooding to Massachusetts, killed at least nine people and knocked out power to about 2.4 million homes and businesses in the Northeast.
Some 100,000 homes and businesses in the region remained without power on Wednesday.
The governors of New Jersey and Pennsylvania declared states of emergency, giving them access to support from the US government if needed.