CNN
 — 

A rapidly intensifying nor’easter will bring heavy snow, winds and coastal flooding Tuesday across the US Northeast, threatening widespread power outages and making travel impossible in some areas.

More than 20 million people were under winter weather alerts early Tuesday ahead of the nor’easter, a type of storm that travels along the eastern seaboard and is typically fed by coastal winds from the northeast.

Widespread snowfall from 6 to 18 inches is likely from northeastern Pennsylvania and far northwestern New Jersey through much of upstate New York and New England, the Weather Prediction Center said. Isolated amounts of more than 2 feet are possible in higher elevations including parts of New York’s Catskill and Adirondack mountains.

Some of it will fall quickly: Rates of 2-3 inches per hour are possible across interior portions of the Northeast, and along the I-95 corridor from southern New England to Portland, Maine.

The combination of snow and strong winds, which could gust up to 55 mph, threatens to down power lines and damage trees, triggering power outages.

“The weight of the snow will be extreme,” David Novak, director of the Weather Prediction Center, said Monday. “It’s known as ‘snow loading’ and has to do with the heavy, wet type of snow we are expecting.”

More than 25 million people were under high wind alerts overnight into Tuesday, including those in Boston, Baltimore and Philadelphia.

Some school districts in interior parts of the Northeast closed or were delaying classes Tuesday, particularly in mountainous areas, as well as in Syracuse, New York, and Worcester, Massachusetts.

Minor beach erosion and coastal flooding is expected along the New England and southern New York coasts due to strong winds, the prediction center forecasts.

Philadelphia and New York City may get small amounts of snow Tuesday afternoon after some morning rain. More snow is possible in Boston – up to around 4 inches near Logan International Airport – and evening drives around Boston may be hindered by snow-covered roads, the National Weather Service warned.

Governors across the Northeast implemented preemptive measures as they braced for snow-covered roads and widespread utility emergencies.

In New York, Gov. Kathy Hochul has declared a state of emergency across dozens of upstate counties that went into effect Monday night.

“New Yorkers should plan for two to three days straight of hazardous winter weather starting tonight,” state Homeland Security and Emergency Services Commissioner Jackie Bray said Monday. “Only travel if absolutely necessary, and keep your phones and other devices charged in case you need to call for assistance during a power outage.”

Maine Gov. Janet Mills has closed all government offices on Tuesday and advised residents to “to stay off the roads if they can, plan for extra time if traveling, and give plenty of space to road crews and first responders working hard to keep us safe.”

The storm will begin to taper off Wednesday as it shifts off the New England coast, according to the weather service.

Some utilities and transit agencies have announced preparations and given advice in anticipation of the storm’s impacts.

Power company ConEdison, which serves New York City and neighboring Westchester County, has brought in more than 400 outside workers to assist with possible outages, the utility said in a news release.

ConEdison warned customers to avoid downed wires – which could be hidden by snow, leaves or water – and report them to the utility or local authorities immediately.

The Metropolitan Transportation Authority, which serves a 5,000-square-mile travel area surrounding New York City, Long Island, southeastern New York state and Connecticut, also announced plans to maintain as much service as possible.

“MTA employees will be deployed throughout the operating region spreading salt and clearing surfaces of snow, keeping signals, switches, and third rails operating, and attending to any weather-related challenges,” a release from the transit authority said.