The novel phenomenon of “thundersnow” rattled New Yorkers and others on the US east coast on Wednesday as they hunkered down working from home or braced for the evening commute through a near white-out as the second “nor’easter” storm in a week blew heavy, wet snow into the region.

Snowfall intensified during the afternoon and was forecast to persist into Thursday as thousands remained without power from the tempestuous wind and rain that hit during the previous storm late last week, bringing flooding to coastal Massachusetts.

Up to a foot of snow is expected to fall on New York City and surrounding New Jersey and Connecticut suburbs, with up to two feet further inland, and wind gusts could create “near-whiteout conditions” for travelers, the National Weather Service said.

The heaviest snow was expected in Maine, where up to 18 inches was possible.

The storm spread with varying degrees of intensity across the north-east, from western Pennsylvania up into New England, the service said.

Around half of all US scheduled flights were canceled at the three major airports serving New York City, according to the tracking service FlightAware. The website said 9,587 flights had been delayed and 3,076 canceled, most of them in the north-east, by late afternoon.

All schools were closed in Philadelphia, while other schools across the region had already canceled classes or shortened the school day ahead of the storm. Accumulated snow and winds up to 60mph are expected to knock down more power lines. Some 100,000 homes and businesses in the region remained without power on Wednesday.

Around lunchtime in parts of New York and New Jersey, long, loud rumbles of thunder crashed through the precipitation in the unusual condition known as thundersnow.

The National Weather Service explained that it infrequently occurs during a fierce snowstorm in a similar way to a thunderstorm with rain. It is an indication of the low, warmer air rising really fast into the sky, hitting the colder high air and falling swiftly as snow. Snow clouds on Wednesday were throwing out the snow at up to three inches an hour.