(CNN) — A rapidly intensifying nor’easter bringing heavy snow, winds and coastal flooding to the U.S. Northeast is already causing power outages and making travel difficult, if not impossible, in some areas.

More than 20 million people were under winter weather alerts Tuesday as a result of the first nor’easter of the season — a type of storm that travels along the Eastern Seaboard and brings winds from the northeast over the region — with up to a foot of snow having fallen in western Massachusetts overnight.

Live updates: Snow, rain and flooding pummel U.S. coast to coast

Here’s what to expect:

• Widespread snowfall is forecast: Six to 18 inches of snow is likely from northeastern Pennsylvania and far northwestern New Jersey through much of upstate New York and New England, per the Weather Prediction Center. Higher elevations, such as New York’s Catskill and Adirondack mountains, could see isolated amounts of more than two feet.

Philadelphia and New York City may get small amounts of snow Tuesday afternoon, but Boston could see up to around four inches near Logan International Airport, the National Weather Service said, warning evening commuters they could face snow-covered roads.

A map showing winter weather alerts issued across the Northeast as of early March 14, with purple indicating winter weather advisories and pink representing winter storm warnings. (CNN Weather)

• It could fall quickly: Snowfall rates of two to three inches per hour are possible across interior portions of the region and along the I-95 corridor from southern New England to Portland, Maine.

• Wind could contribute to power outages: In addition to snow, strong winds — with gusts of 45 to 65 miles per hour — threaten to damage trees and bring down power lines. It could also contribute to minor beach erosion and coastal flooding along the New England and southern New York coasts, prediction center said. More than 25 million people were under high wind alerts Tuesday, including those in Boston, Baltimore and Philadelphia.

The storm will begin to taper off Wednesday as it shifts to off the New England coast, according to the weather service. But the impacts have already been felt.

More than 260,000 customers were without from New York to New Hampshire, according to PowerOutage.us — a number that was rapidly rising throughout Tuesday morning.

Meanwhile, Tuesday was shaping up to be a day of headaches for travelers across the region, with hundreds of flight delays and cancellations in the U.S., according to FlightAware.

A ground stop was in effect at LaGuardia Airport in New York, with delays of about two hours, according to the Federal Aviation Administration. The agency warned ground stops were possible at Newark Liberty International Airport and John F. Kennedy International Airport.

Upstate, the nose gear of a Delta Air Lines plane went beyond the paved taxiway at Syracuse Hancock International Airport while taxiing for departure to LaGuardia, the FAA said.

Officials and power utilities prepare

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

New York Gov. Kathy Hochul 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 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 city of Worcester, Massachusetts is prepared to assist residents with burst pipes, City Manager Eric Batista told “CNN This Morning” on Tuesday.

“Right now, the biggest concern for residents is to make sure they stay home and they stay safe,” he said.

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.

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.

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, 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.

The-CNN-Wire™ & © 2023 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.