CNN  — 

Heavy snow and strong winds are expected to slam some metro areas in the Northeast this weekend, with millions already under winter storm watches.

Forecasters predict eastern Massachusetts, including Boston, and Rhode Island will see 12 to 24 inches of snow that could begin falling late Friday through the day Saturday, combined with wind gusts up to 60 mph.

The National Weather Service in Boston warns that snowfall rates of 3 to 4 inches per hour will be possible and could produce extreme snowfall totals. “With this forecast package, we have capped the totals at 24 inches. But if we get more confidence, the forecast amounts for southeastern MA could go up into the 30 to 36 inches range,” it said.

More than 42 million people – including in Philadelphia, New York and Boston – were under winter storm watches as of Thursday afternoon for snow that could be heavy, according to the National Weather Service.

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The storm is expected to form Friday in the Atlantic Ocean just off the coast of Georgia, then rapidly strengthen – a process known as bombogenesis – overnight Friday and track Saturday up the East Coast, though specifics on the impact remain unclear.

“This storm is likely to strengthen at a rate, and to an intensity, equivalent to only the most powerful hurricanes, so the high-end potential of this storm cannot be overstated,” CNN meteorologist Brandon Miller said. “But with nor’easters, like in real estate, it will all come down to location, location, location.”

Heavy snow and strong winds are likely across New England, “which could lead to blowing snow, scattered power outages, and some damage,” the Weather Prediction Center said early Thursday.

Moderate to heavy snow is possible from northeast North Carolina to New York, “but confidence in potential impacts is much lower,” the forecasters said.

The storm could dump up to 8 inches of snow in Philadelphia and New York City, according to multiple forecast models.

The National Weather Service office for Washington and Baltimore said that 2 to 4 inches of snow could come down in parts of Virginia and West Virginia.

The double threat of heavy snow and strong winds has the potential to create blizzard-like conditions throughout the Northeast. A blizzard occurs when snow is joined by winds gusting over 35 mph for more than three hours and creates visibility of less than a quarter of a mile.

The American model (move bar to the left) shows less snow due to the storm tracking farther from shore, while the European model (move bar to the right) indicates more snow across the region due to a storm track just offshore.

Coastal flooding is a possibility

It’s still too early to predict the precise impact of the storm and snowfall totals.

“The storm track remains uncertain which will have a direct impact on accumulations and where heaviest snowfall sets up,” the weather service office in Boston said Thursday morning.

How to survive a blizzard

A “farther offshore track of the low will decrease snow amounts while a track closer to shore will increase snow amounts and if the low gets close enough to the coast, a wintry mix will be possible for some eastern coastal sections (This is looking less and less likely),” the New York office of the National Weather Service said Wednesday.

“We can’t rule out a shift back to the west or even a further eastward shift with less snow,” forecasters said early Thursday.

Besides gusting wind and blowing snow, coastal flooding may also be in store for some places. “Significant coastal impacts are possible in the Northeast, including coastal flooding and beach erosion,” the prediction center said.