Up to two feet (60cm) of snow is expected to fall along the east coast of the US on Wednesday, with officials warning it could be the biggest winter storm for years.
As many as 50 million people could be affected by the snowfall, which is expected to stretch from North Carolina up through New England in the north east.
“For much of the area, right along the coast, we are going to have a mix of rain, snow and maybe some sleet and freezing rain,” said Sarah Johnson, a weather service meteorologist in New Jersey.
“As you get farther inland, you will see more predominant snow.”
Mayor of New York City Bill de Blasio asked people to “take it seriously” in a message posted online.
Mr de Blasio added there could wind gusts of up to 50mph and snow cover of 30cm, urging New Yorkers to take precautions ahead of the storm’s arrival.
Salt spreaders and snow ploughs will be in operation across the city, the mayor said, telling commuters to either use public transport, or stay at home to work.
In a message to parents, he told them to “be ready with an alternative for Thursday in case the snow is bad enough that we have to close the school buildings”.
Dashing hopes of a snow day, he added that with the introduction of remote learning, children will still be required to study if they have to remain at home, “whether they’re happy about it or not”.
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The heaviest snowfall is expected across Maryland and Pennsylvania, with places like Boston in Massachusetts and Washington DC also being hit hard.
It is likely to be the first major storm of the season, which tends to last until around March, threatening the region with disruption for months.