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A mighty nor'easter threatening to dump as much as 2 feet of snow on large parts of the Northeast was snarling air travel across the country and throwing major cities in the region into chaos Monday night.

"We're not kidding with this. This is not some sort of joke," said Kait Parker, a meteorologist for The Weather Channel. "This is a major storm."

With parts of eight states — including New York City — under a National Weather Service blizzard warning through Tuesday evening, almost 5,300 arrivals and departures scheduled for Tuesday were pre-emptively canceled.

More than half them, 2,580, were at the three New York City-area airports alone: John F. Kennedy, LaGuardia and Newark. In New York City, above-ground train service will be suspended starting at 4 a.m.

An army of snow plows and other equipment marched onto sunny Northeastern streets Monday afternoon ahead of the winter wallop, which was forecast to kick off late in the evening with light snow, intensifying overnight into early Tuesday.

The storm could drop 18 inches of snow or more on New York City, with fierce wind gusts of 40 mph to 50 mph. Mayor Bill de Blasio pleaded with chilly New Yorkers to keep off the roads so sanitation crews and first responders can do their jobs.

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New York Gov. Andrew Cuomo declared a state of emergency statewide, activated 2,000 National Guard personnel and told non-essential state employees to take Tuesday off.

"It's a good day to stay home," Cuomo said Monday. "It's going to be a dangerous, dangerous situation."

In Connecticut, Gov. Dannel Malloy banned travel statewide beginning at 5 a.m. ET Tuesday.

New York, Boston and Philadelphia all said schools would be closed Tuesday. The federal Office of Personnel Management said it would wait until 3 a.m. Tuesday to decide whether federal offices in the Washington, D.C., area would close.

Airports from Chicago to Boston bunkered in for the storm. At 9:30 p.m. ET, more than 5,200 of Tuesday's arrivals and departures had been scrubbed. Many airlines said they would waive rebooking fees for mid-Atlantic and Northeast airports.

Because the United States' aviation system is so interconnected, the chaos in the Northeast created a ripple effect through the rest of the country: There were long lines of frustrated travelers at the Miami and Fort Lauderdale, Florida, airports, where scores of flights to Northeast hubs were scrubbed.

Airline passengers wait to rebook canceled flights Monday at Miami International Airport. Alan Diaz / AP

The heaviest snow was expected to blanket the East on Tuesday morning, holding steady through the afternoon, with snowfall as much as 2 to 4 inches an hour.

"The winds are going to be blowing up over 60 miles an hour, which means your visibility is going to be next to nothing," Parker said.

And when the snow combines with gusts like that, there's also the potential for power failures, falling trees and traffic accidents.

"This is when the snow will be falling so hard and blowing around so much [that] cars and trucks will be at risk of getting stranded," NBC News meteorologist Bill Karins said.

"The storm is going to start, and when it starts, it's going to snow hard, and it's going to snow quickly," Massachusetts Gov. Charlie Baker said at a news conference Monday night. "It's going to create very treacherous circumstances and conditions."

Winter Storm #Stella's main event is underway as #blizzard warnings cover parts of 8 states: https://t.co/WqrbiskK0t pic.twitter.com/D0wAtfcOlE — The Weather Channel (@weatherchannel) March 14, 2017

That's unwelcome news for many in the region, who were enjoying springlike temperatures a few days ago and were hoping the storms were done for the season.

"This will be our 12th plowing storm this year. We budget for eight," Steve Earley, public services director in Portland, Maine, told New England Cable News. "It's been a busy winter, for sure."

At Rocky's Hardware in Agawam, Massachusetts, meanwhile, Joe Beaudry picked up a snow blower, shovels and a roof rake because you can never really be sure the storms are over.

"With New England, you never know," Beaudry told NBC station WWLP of Springfield. "We could get one in April."