WASHINGTON >> A blizzard menacing the Eastern United States started dumping snow in Virginia, Tennessee and other parts of the South on Friday as millions of people in the storm’s path prepared for icy roads, possible power outages and other treacherous conditions.

Snowfall as heavy as 1 to 3 inches an hour could last for 24 hours or more in some areas, said meteorologist Paul Kocin with the National Weather Service. That puts estimates at more than 2 feet for Washington, a foot to 18 inches for Philadelphia and 8 inches to a foot in New York.

Kocin compared the storm to “Snowmageddon,” the first of two storms that “wiped out” Washington in 2010 and dumped up to 30 inches of snow in places, but he said the weekend timing and days of warning could help limit deaths and damage.

At sunrise in Memphis, Tennessee, ice covered parked cars after an overnight dusting of snow. Roads were manageable, but downtown was quieter than usual. Danielle Aldridge couldn’t find her ice scraper, so she used a plastic kitchen cutting board on her windshield. She had to get to work as a nurse at a family practice clinic. Unlike government offices and many private businesses in the city, the clinic is open Friday.

“Sick people will come in today,” she said. “That’s part of the deal. Like the post office — rain or shine or sleet or snow, I will take care of my patients.”

In the mountains of Craigsville, West Virginia, people bought the usual kerosene heaters, propane tanks and gas cans, but also a special item: a rake that helps homeowners get snow off their roofs.

“It’s going to be bad, probably,” said Missy Keaton, cashier and office secretary at the town’s hardware store, called Hardware, That’s Us. But she said many people are prepared after snow from Superstorm Sandy caused numerous roof collapses — at stores, homes and a hardware plant — in nearby Summersville in 2012.

At a supermarket in Baltimore, Sharon Brewington stocked her cart with ready-to-eat snacks, bread, milk and cold cuts. In 2010, she and her daughter were stuck at home with nothing but noodles and water.

“I’m not going to make that mistake again,” she said.

As food and supplies vanished from store shelves, five states and the District of Columbia declared states of emergency ahead of the slow-moving system. Schools and government offices closed pre-emptively. Thousands of flights were canceled. College basketball games and concerts were postponed.

The snowfall, expected to continue into Sunday, could easily cause more than $1 billion in damage and paralyze the Eastern third of the nation, weather service director Louis Uccellini said.

“It does have the potential to be an extremely dangerous storm that can affect more than 50 million people,” Uccellini said at the Weather Prediction Center in College Park, Maryland.

The director said all the ingredients have come together to create a blizzard with brutally high winds, dangerous inland flooding, white-out conditions and even the possibility of thunder snow.

Washington looks like the bull’s-eye, Uccellini said. White House spokesman Josh Earnest said President Barack Obama would hunker down at the White House.

The federal government says its offices will close at noon Friday. The capital’s subway system will shut down late Friday and remain closed through Sunday.

In northern Virginia, the bishop of Arlington gave Catholics in his diocese the OK to stay home from Mass on Sunday. The Most Rev. Paul Loverde cited serious travel concerns in his statement.

And in Washington, the archdiocese will remind people that dangerous travel conditions are a legitimate excuse for missing the Sunday Mass obligation. Both archdioceses encourage those who miss to watch a televised Mass.

New York City is just inside the storm’s sharp northern edge. It’s likely to see heavy accumulations, but Boston will probably get off easy this time, forecasters said.

More than just snow is coming. Uccellini said it won’t be quite as bad as Superstorm Sandy, but people should expect high winds, a storm surge and inland flooding from Delaware to New York. Other severe but nonsnowy weather is likely from Texas to Florida as the system chugs across the Gulf Coast, gaining moisture.

Blizzard warnings or watches were in effect from Arkansas through Tennessee and Kentucky to the mid-Atlantic states and as far north as New York.

Train service could be disrupted by frozen switches, the loss of third-rail electric power or trees falling on wires. About 1,000 track workers will be deployed to keep New York’s subway system moving, and 79 trains will have “scraper shoes” to reduce icing on rails, the Metropolitan Transit Authority said.

All major airlines have issued waivers for the weekend, allowing passengers to rebook onto earlier or later flights to avoid the storms. More than 2,400 flights were canceled in the U.S. Friday, and another 2,400 Saturday, according to the flight tracking service FlightAware. The bulk of Friday’s cancellations were in Charlotte and Raleigh, North Carolina; Saturday’s cancelations center on Philadelphia, Washington, and — to a lesser extent — New York. By Sunday afternoon, airlines hope to be back to full schedule to handle business travelers heading out for the week.

One major event in Washington was still on: the March for Life, an annual anti-abortion rally that’s usually one of the largest events on the National Mall. It will be held Friday, the anniversary of the Supreme Court’s Roe v. Wade decision.

The U.S. Capitol Police said sledding on Capitol Hill — which only recently became legal after an act of Congress — would be welcome for the first time in decades, as long as conditions are safe.

While some people and businesses worried about the snow, at least one industry could see a potential boon: ski resorts. Many got a late start on the season because of record high temperatures in December.

“There is never too much snow on the slopes,” said Joe Stevens, spokesman for the West Virginia Ski Areas Association.

Borenstein reported from College Park, Maryland. Associated Press writers Juliet Linderman in Baltimore; Jessica Gresko in Washington; Adrian Sainz in Memphis, Tennessee; John Raby in Charleston, West Virginia; and AP Airlines Writer Scott Mayerowitz in New York contributed to this report.