A day after the official beginning of spring, the storm is bringing heavy snow, strong winds and possible coastal flooding to some areas. It has the potential to be one of the most significant and disruptive snowstorms for so late in the season, CNN meteorologists said.
"If the current forecast pans out, this nor'easter will dump more snow on Washington, Philadelphia and New York than the three earlier storms combined," CNN meteorologist Brandon Miller said.
More than 70 million people were under a winter storm watch, warning or advisory from the southern Appalachians to Boston.
Pennsylvania Gov. Tom Wolf told reporters that it's "a huge snowstorm that's only going to get worse."
The storm will move away from the region by Thursday but not without first hitting coastal New England and Maine.
• About 4,400 US flights were canceled due to the storm, according to the tracking site Flightaware.com
• Public schools in New York City, Philadelphia and the District of Columbia were closed.
• By Wednesday evening, the storm had dumped 4 inches of snow on Washington, DC, five inches on New York's Central Park and 4 inches in Philadelphia.
Snow disrupting nation's capital
Areas west and north of Washington are likely to see close to a foot of snow.
"It's been 75 years since Washington has had 5 inches of snowfall or greater this late in the season," Miller said.
The inclement weather caused closures for much of the federal government. The White House and State Department canceled all public events for the day. However, the House and Senate are planning to work Wednesday as Congress tries to finalize a spending deal.
First lady Melania Trump tweeted a photo: "Snow Day @WhiteHouse."
Philadelphia could see up to a foot of snow. The City of Brotherly Love may get its biggest snowfall after the first day of spring in more than 100 years.
For those in other parts of Pennsylvania, the storm was already well underway Wednesday morning. Thile Kreider posted an Instagram video of the snow blanketing her yard in Manheim.
Pennsylvania Transportation Secretary Leslie Richards said the brunt of the storm could bring up to three inches an hour, with potential whiteout conditions.
The governor said snow is expected until midnight but that roads should clear up quickly after then. He warned there would be downed tree limbs and power lines.
State of emergency in New Jersey, parts of New York
Wind gusts and snow had reached New Jersey and New York City by Wednesday morning.
New Jersey Gov. Phil Murphy declared a state of emergency Tuesday night. He urged people to stay home and said a ban was in place for commercial and recreational vehicles and motorcycles on highways such as Interstate 78.
New York Gov. Andrew Cuomo also declared a state of emergency in New York City and Putnam, Rockland, Westchester, Nassau and Suffolk counties.
In New York City, accumulation of a foot to 18 inches of snow is expected before the storm departs early Thursday, Mayor Bill de Blasio told reporters.
With these late winter storms, it is difficult to predict snowfall amounts because of the mixing of warmer air. In some of the earlier nor'easters, the air near the ground has stayed warm enough that some places have seen lots of snow fall from the sky but had little accumulation. An urban heat island effect is plausible once again with this spring storm.
Boston stayed on the warmer side in the first two nor'easters but then got walloped with snow during the third storm this month. The city is likely to see another 6 to 8 inches of snow, adding to the 20-plus inches it has already received in March.
If Boston gets 10 inches, the city would have its third snowiest March on record.
These late winter storms are likely to become more frequent with climate change
. A study last week in the scientific journal Nature Communications ties extreme winter weather, specifically major snowstorms in the Northeast, to warming Arctic temperatures.
Blizzard conditions likely
With a forecast of heavy snow and winds more than 45 mph, blizzard conditions are possible.
Coastal areas such as Cape Cod in Massachusetts are predicted to receive gusts up to 60 mph to Thursday.
Flooding is a threat along the coast from Virginia to Massachusetts. Some of the worst coastal flooding could occur along the Jersey Shore, with high tides of 2 to 3 feet above normal possible.
This will put a strain on already vulnerable coastal areas, which saw dramatic storm surges from the nor'easters over the last three weeks.