Millions of Americans awoke Saturday to heavy snow outside their doorsteps as a mammoth winter storm crawled up the East Coast, making roads impassable, shutting down mass transit and bringing the nation's capital and its largest city to a standstill.

Most people seemed to heed warnings to stay home and off the roads, which were largely deserted. But more was yet to come, with blizzard conditions expected to persist throughout the day. In addition to snow and hurricane-force winds, the National Weather Service predicted up to half an inch of ice for the Carolinas and potentially serious coastal flooding for the mid-Atlantic region.

"Find a safe place and stay there," Washington Mayor Muriel Bowser implored residents and visitors alike.

Snow fell from the Gulf Coast to New England. In nearly two dozen places, it passed the 20-inch mark by late morning, according to the weather service. Terra Alta, West Virginia, reported 28 inches.

At least 10 deaths were blamed on the system, most of them in traffic accidents.

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The long-anticipated storm lived up to expectations, except overnight it started to look even bigger. So forecasters increased their snow predictions for New York and points north.

The new estimates were for heavy snow all the way up to just south of Boston, said forecaster Patrick Burke at the weather service's Weather Prediction Center in College Park, Maryland.

Eighteen to 24 inches were predicted for Washington, Baltimore and Philadelphia; 24 to 30 inches for areas just north and west of Interstate 95 outside those two cities; and 15 to 20 inches for New York, Burke said.

"This is kind of a top 10 snowstorm," said weather service winter storm expert Paul Kocin, who co-wrote a two-volume textbook on blizzards. And for New York and Washington this looks like top 5, he said. "It's a big one."

In Kentucky, where some places got 18 inches on Friday, drivers on a long stretch of Interstate 75 south of Lexington got stranded overnight because of a string of crashes and blowing snow. The road was closed, but reopened early Saturday, with traffic moving slowly, officials said.

It was unclear exactly how many were stuck. Crews passed out snacks, fuel and water and tried to move cars one by one. Emergency shelters were opened.

Motorists also were reported stranded along pockets of the Pennsylvania Turnpike near the Allegheny Mountain Tunnel in Somerset County. The National Guard was called to help, said turnpike spokesman Carl DeFebo.

In the Washington metro area, nearly 2 feet of snow was on the ground by Saturday morning, and monuments that would normally be busy with tourists, were mostly vacant. All mass transit was to be shut down through Sunday.

In Silver Spring, Maryland, about 20 inches of snow had fallen by daybreak. Plows cleared a heavily traveled road for ambulances and trucks, but few other vehicles were moving. A couple of intrepid people walked along the cleared portion of the road, ducking into the deeper snow when vehicles approached.

The snow alone would have been enough to bring the East Coast to a halt. But it was whipped into a maelstrom by brutally sharp winds that reached 75 mph at Dewey Beach, Delaware, and Langley Air Force Base, Virginia, the weather service reported.

From Virginia to New York, sustained winds topped 30 mph and gusted to around 50 mph, Burke said.

The wind was so strong that scientists reported trouble measuring the snowfall.

And if that weren't enough, the storm had bursts of thunder and lightning. Forecasters saw lightning out the window of the Weather Prediction Center, where meteorologists were camped out.

In New Jersey, 40,000 customers were without power early Saturday, most of them along the coast.

Even before the snow began to fall Friday afternoon, states of emergency were declared. Lawmakers went home, and schools, government offices and transit systems closed early from Georgia to New York.

The ice and snow made travel treacherous and caused thousands of accidents. By late Friday, Virginia State Police reported 989 crashes statewide and had assisted nearly 800 disabled vehicles, spokesman Ken Schrad said.

About 7,600 flights were canceled Friday and Saturday — about 15 percent of the airlines' schedules, according to the flight-tracking service FlightAware. They hope to be fully back in business by Sunday afternoon.

One of the unlucky travelers stranded by the storm was Jennifer Bremer of Raleigh, North Carolina. She flew into Chicago on Thursday, carrying only a briefcase, for what she thought would be less than a day of meetings. Her flight home was canceled Thursday night, then again Friday.

"I have my computer, my phone and a really good book, but no clothing," Bremer said Friday as she eyed flight boards at O'Hare Airport. "I have a travel agent right now trying to get creative."

Not so unhappy to be stranded were passengers on a cruise ship that was supposed to return to the port of Baltimore from the Bahamas on Sunday. Their arrival has been delayed until at least Monday.

The snowstorm was greeted happily at Virginia's ski resorts.

"We're thrilled," said Hank Thiess, general manager at Wintergreen ski resort in central Virginia. "Going forward, we're set up to have just a terrific second half of the ski season."

He said he was expecting 40 inches of dry, powdery snow, perfect for skiing.

"We're going to have a packed snow surface," he said, "that will just be outstanding."

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