NEW YORK (BLOOMBERG) - A foot or more of snow could blanket the Mid-Atlantic and Northeast starting Wednesday, snarling travel and sparking power outages while bringing New York its worst December storm in 10 years.

New York could get 20-30cm of snow starting Wednesday afternoon (Dec 16), lower than earlier estimates as the worst of the storm is now expected to strike further inland the National Weather Service said. The heaviest snow will land in eastern Pennsylvania and western New Jersey, where as much as two feet may pile up.

"There is going to be a large swath from central Pennsylvania to southern New England that could see over a foot," said Tyler Roys, a meteorologist with AccuWeather Inc.

"It's been a while since we've had such an impactful storm."

The storm threatens to snarl road, rail and air traffic throughout the eastern US, just as trucks carrying Pfizer's Covid-19 vaccine from Michigan fan out across the country and carriers are burdened with holiday packages.

It's also likely to touch off power outages and cast many people working from home into the dark, said Zack Taylor, a forecaster with the US Weather Prediction Centre.

"New York City has developed a plan to ensure vaccines continue to be delivered, stored, and administered safely as this storm hits the city," said Bill Neidhardt, press secretary to Mayor Bill de Blasio.

"NYC Emergency Management is poised to assist vaccine deliveries if the need arises, which hopefully won't. Hospitals will continue to vaccinate their frontline staff and doses remain secured in ultra-cold storage."

De Blasio said the city will allow restaurants to continue operating on sidewalks, if possible, but must shut down curb-side dining in streets during the storm. As of 2pm Wednesday restaurants must close any temporary structures that extend from sidewalks into the street, the mayor said.

Street-dining may resume as early as Thursday night if feasible, the mayor added.

De Blasio urged motorists to stay off city streets the next two days for their safety and to permit ploughing.

"We are very concerned about a lot of traffic coming in and then having a lot of problems getting out, he said.

"Thursday morning could be a big mess." Winter storm warnings and watches, as well as weather advisories, stretch from Georgia to Maine. Washington could get from 1 to 2 inches (2.5-5cm), and Philadelphia 7 inches (17.7cm), while Boston could get 11 inches (28cm) along with coastal flooding, according to the National Weather Service."The heaviest amounts will be west of the I-95 corridor," Taylor said.

Cold air will descend from Canada overnight Tuesday into Wednesday and drive temperatures down, said Rob Carolan, a meteorologist at Hometown Forecast Services.

The heaviest snow will probably miss the ski areas of northern New England in favour of slopes in southern New York and Pennsylvania, as well as the Berkshires, Carolan said.

'Exceptional storm'

"It is an exceptional storm for the Poconos," he said. "Eastern Pennsylvania is going to do real well."

In Washington, where snow should start Wednesday morning, the suburbs to the north may get three times as much snow as the city itself. The system's actual path will determine if the forecasts are on target, or if rain and sleet mixes in to reduce snowfall totals.

"There is still some uncertainty from DC to Philly, where that transition between rain and snow and wintery mix will be is quite fine," Taylor said.

If the forecast bears out, this would be the heaviest December snowfall in New York's Central Park since 2010, when the city was buried under 20.1 inches, according to weather service records. It will also beat last winter's total snowfall, which only amounted to 4.8 inches.

Winter storms caused US$2.1 billion (S$3.3 billion) in insured losses across the US last year and about US$3 billion in 2018, according to Munich Re.

The snowy and icy weather snarls airline, highway and rail traffic, and can trigger power outages and hinder retail sales. In 2019, 13 people died across the US from winter weather, according to the National Weather Service.