(CNN) With a blizzard barreling toward the Northeast, the region ramped up preparations and hurried up warnings Monday evening, closing schools, canceling flights and telling residents to get ready.

"This is the storm that's coming," Boston Mayor Marty Walsh said Monday at a news conference on storm preparations. "We are going to get hit."

Among major developments:

— Boston, Philadelphia and New York City school districts will be closed Tuesday along with many government offices.

— Airlines canceled over 6,500 US flights scheduled for Tuesday, according to Flightaware.com.

— New York City could get up to 20 inches of snow, Mayor Bill De Blasio said, with coastal flooding and wind gusts as high as 40 to 50 mph also forecast.

— Parts of Massachusetts could see 24 inches or more and similarly powerful winds, said Gov. Charlie Baker.

— In Philadelphia, where snow was expected to start falling around 9 p.m. Monday, accumulations will likely range from 8 to 12 inches, with a worst-case scenario of 20 inches said Samantha Phillips, the city's director of emergency management."We urge people to prepare for a high impact event," she said.

— In Virginia, the Coast Guard closed the Port of Virginia on the harbor at Hampton Roads. In a news release Monday night, the agency said 50 mph winds predicted from the pending storm could create hazardous conditions that would make it difficult for Coast Guard units to reach any distressed mariners. "There is a real danger to all vessels on the water," said Capt. Rick Wester, the captain of the port. "I strongly recommend that mariners stay in port."

— "Wherever you are at sunrise Tuesday morning, expect to remain there throughout the remainder of the storm and into (Tuesday) night," said Connecticut Gov. Dannel Malloy. A statewide travel ban was scheduled to go into effect Tuesday at 5 a.m. throughout Connecticut.

Blizzard warnings and watches for the region, including northeastern New Jersey, southeastern New York and southern Connecticut, as well as Boston, Philadelphia, Baltimore and Washington, were issued by the National Weather service.

Travel warnings, sand and salt for streets

Philadelphia was ready to deploy a full snow operation that includes 400 pieces of equipment and 50,000 tons of salt, said street commission member Carlton Williams. Residents could expect to wait a week for trash collection service to resume.

Warnings to use caution came from public officials up and down the East Coast -- including the President.

"Everyone along the east coast be safe and listen to local officials as a major winter storm approaches," President Donald Trump tweeted.

Everyone along the east coast be safe and listen to local officials as a major winter storm approaches. @NWS https://t.co/NXfRqQcUgb https://t.co/ovgwMRSIbS — President Trump (@POTUS) March 13, 2017

This storm system already hit the Midwest, claiming two lives in Wisconsin. According to the Milwaukee County Medical Examiner's office, the victims -- both men -- died in separate weather-related activities. One man, 76, was operating a snow blower before he died; the second man, 64, was shoveling snow, said investigator Jenni Penn. They were both cardiac-related deaths, said Penn.

In addition to the hazards produced by a deluge of snow, the region also is expecting downed power lines and service interruptions.

"This should be a very serious blizzard, one that everyone should take seriously," New York's de Blasio said.

Here is a look at simulated radar output from one of today's computer models runs (NAM) to give some perspective on the timing of the storm. pic.twitter.com/FgXBEILzMK — NWS Eastern Region (@NWSEastern) March 13, 2017

The snow is expected to begin after midnight in New York City. The period of greatest accumulation should be between 6 a.m. and noon Tuesday, with a possible 2 to 4 inches per hour and whiteout potential during that time, de Blasio said.

Blizzard Watches upgraded to Blizzard Warnings except across E Suffolk and SE CT where Winter Storm Warnings were issued. Briefing to come. pic.twitter.com/zkY8v5EmIy — NWS New York NY (@NWSNewYorkNY) March 13, 2017

Baker provided similar details about what's expected in Massachusetts, saying the state expects sleet, rain and extremely cold temperatures along the coast.

"This is going to be a lot of snow and it's going to be a mess," Baker said.

A snow emergency will go into effect in Boston at 7 a.m. Tuesday, Boston mayor Walsh said, after 450 sanders pretreat streets Monday night and early Tuesday. The city's salt supply for streets is at 36,000 tons, he said.

Walsh added a warning for anyone trying to save parking spots on city streets during the snow emergency: Don't do it.

"I'm not going to put city resources on that," he said, leaving it up to drivers to figure out what might happen to their vehicles.

New York Gov. Andrew Cuomo activated the State Emergency Operations Center for Monday evening. State agencies have already deployed personnel, assets and state stockpile resources -- including sandbags, generators and pumps -- to key areas.

Cuomo urged commuters to drive carefully and avoid unnecessary travel. Motorists, especially tractor trailers, should be prepared for road closures across the state, he said.

Travelers should expect delays.

American Airlines canceled more than 450 flights Monday and 1,450 Tuesday due to the storm. The alert covers 40 airports — including hubs in Chicago, New York, Philadelphia and Washington. Passengers may rebook without change fees, the airline said.

Amtrak said it will operate a modified schedule in the Northeast region on Tuesday. It advised passengers with reservations to monitor conditions and make changes before their scheduled departure using Amtrak.com or the company's mobile apps.

Travel restrictions on the Pennsylvania Turnpike were scheduled go into effect at 10 p.m. Monday for all interstates and expressways east of Interstate 99, said Gov. Tom Wolf. Those restrictions set a 45 mph speed limit, and a ban on tandem truck trailers, empty or towed trailers, buses, recreational vehicles and motorcycles.

It's a winter wonderland on social media

From the Midwest to New England, Americans used social media to share images of the severe weather.

An Instagram post captured a crewman at Chicago's Midway International Airport de-icing an early flight.

De-icing before an early flight. #chicagowinter #springforward A post shared by Curtis Kuhn (@curtiskuhn) on Mar 13, 2017 at 4:40am PDT

Also in the Windy City, the Chicago Loop sculpture made a striking image in the snow.

❄❄⛄⛄❄⛄❄⛄❄⛄⛄⛄⛄⛄⛄⛄⛄⛄⛄⛄⛄🌀🌀💟💟 A post shared by Marcin Beliczynski (@marcinb38hairstylist) on Mar 13, 2017 at 6:34am PDT

Shoppers began tweeting photos of long lines and empty shelves at grocery stores.

No 'year without winter' after all

Ahead of the storm, bone-chilling temperatures persisted across the region.

"Nearly one in every three people in the US are under a winter weather alert of some sort," CNN meteorologist Pedram Javaheri said. "This all comes after what seemed like it would be the year without a winter."

Less than two weeks ago, the nation's capital was enjoying 80-degree temperatures.

Forecasters expect Washington will get off easy, with 5-10 inches of snow.

It is not uncommon for significant snow to fall in March in #NYC. Here are the top 5 snowfalls March 1 or later since 1869. pic.twitter.com/dCDU9NiUOA — NWS New York NY (@NWSNewYorkNY) March 12, 2017

"We have two low-pressure systems essentially coming together to create a potentially significant Nor'easter," CNN meteorologist Allison Chinchar said.

"The first low begins in the Midwest and progresses east to the mid-Atlantic region. The second low begins off the coast of Florida and moves north along the East Coast and meets up with the first low around Washington, D.C."

"Since January 1, we have seen over 9,000 record high temperatures set in the US -- compare that to only 1,300 record low temperatures this winter, a 9 to 1 ratio favoring warmth," Javaheri said.

February 2017 finished as one of the warmest February's on record across the Eastern US. Winter 2016-17 (Dec-Jan-Feb) also among the warmest pic.twitter.com/0TuhkzfT9w — NWS Eastern Region (@NWSEastern) March 2, 2017

Despite the advance of colder temperatures across the Eastern United States, last month was one of the warmest on record, the National Weather Service tweeted.