A day of dreadful weather gave way to treacherous conditions after nightfall Sunday, and the sleet and freezing rain that caked streets and sidewalks portended a messy start to the workweek.

Faced with the prospect of sending school buses onto icy streets, Loudoun County announced that its schools would be closed Monday, followed by Fairfax, Prince William and Fauquier counties. D.C. schools, as well as the city government, will operate under a two-hour delay.

With days of warning and roads virtually empty Sunday afternoon and evening, highway crews were prepared to cope with the storm, which brought several inches of snow in some parts of the region and then turned to a mix of sleet and rain.

A pause in the rain came about 8 or 9 p.m. Sunday, and traffic in the region appeared to be flowing relatively smoothly. But predictions were for more rain early Monday, which was expected to coat the cold ground with ice.

A National Weather Service forecast predicted ice accumulations after midnight in the Washington area of one-tenth to one-quarter of an inch.

“Please keep speeds down,” the Maryland State Highway Administration urged in a statement.

One of the greatest disruptions caused by the storm Sunday occurred on Interstate 81 in the Hagerstown area of Maryland’s Washington County, where the Associated Press reported that chain-reaction crashes delayed snow removal for hours. The crashes began before noon, and a state police duty officer said the road did not reopen fully until about 4:30 p.m.

In Montgomery County, highway chief Keith Compton said that his crews expected to have all primary and side streets salted by late Sunday night and that they would return to renew the application at 3 a.m. Monday.

Metro officials said early Sunday evening they did not think the weather would have any impact on Monday’s rail service but that bus riders should allow extra time.

Power outages did not present any major problem through the day on Sunday. Near midnight, 1,450 outages were reported in Northern Virginia, with a total of about 2,300 outages across the D.C. region. But it was unclear what might happen overnight if icing continued.

Those who suffered the weather’s worst Sunday were fans of the Washington Redskins, who sat through snow and sleet before most headed for FedEx Field’s exits at halftime of the game, which the home team lost, 45-10.

“The snow and pregame enthusiasm are changing to freezing rain and reality as the hapless Skins are outmatched early by the playoff-bound Chiefs,” said Chris Scott of Linthicum, Md., who watched from Section 424.

Sam Barone of Bethesda hung in to the end, although he realized it might mean a slow, slippery trip home after the game.

“I guess I’m loyal,” Barone said after scraping the ice off the windshield of his silver Volkswagen. “I’ve never seen FedEx under snow, so it was exciting.”

Fear of dangerous driving also put a damper on Christmas shopping, with some merchants reporting that the day fell short of their hopes.

By late Sunday night, many flights scheduled to depart from Dulles International Airport had been canceled. It appeared that most flights scheduled to leave Reagan National were operating, based on information from the airports. Amtrak passengers also experienced delays for several trains at Union Station.

“We chose the train over driving because we knew the weather would be bad,” said Mike Ruszkowski of Norfolk, Va. “I travel a lot for work. I’m used to it.”

Hyewon Yang, 29, carried a freshly baked pizza back to her North Bethesda home Sunday on foot. She was shielded from the wintry mix by an oversize umbrella and was bundled up in a hat, scarf, mittens and boots.

She had not wanted to call for delivery, she said, because she didn’t want to ask someone else to drive in bad weather when she wouldn’t. “It’d be a really mean thing to do,” she had decided.

In Alexandria, the string of bright white lights over the outdoor Christmas tree stand was coated in ice and volunteers spent the day shoveling snow and slush from the sidewalk around the Church of St. Clement. “We’ve sold about 26 trees today,” said Casey Clark, his face red from the cold as he bundled up the blue twine used to secure the trees to the tops of cars. “The weather may be terrible, but people are in good spirits.”

At the National Gallery of Art’s Sculpture Garden Ice Rink, Lorieth Scarleth tottered along the rink’s edge, fat flakes of snow falling onto her black trench coat, and a skating instructor took her by the hand to lead her around a class of toddlers in snow suits.

Scarleth, 27 and a secretary in Panama City, had always wanted to see snow. So when she and her boyfriend, Julio Mou, 38, saw news about a storm on a weather channel, he bought plane tickets for a weekend trip to Washington. Just to make her smile.

Skaters whirled around them, tracing lines like calligraphy. Scarleth and Mou held tightly to the railing, circling the rink slowly. They made it three times around without crashing.

A new song came over the loudspeakers, Percy Sledge’s “When a Man Loves a Woman.” Mou had a diamond ring in his pocket; he had decided that he was going to ask Scarleth to marry him sometime before Jan. 1.

So he asked a man at the rink for help. He wanted to be in the center of the rink. A worker guided the two of them out there.

Mou took out the ring. Scarleth opened her mouth, in shock.

And she said: “Yes! Yes, of course I want to be your wife!”

While they hugged, unsteadily, skaters around them stopped and clapped.

Lori Aratani, Leah Binkovitz, Michael Laris, Ann E. Marimow, Donna St. George, Brigid Schulte, Susan K. Svrluga, Bill Turque, Rachel E. Weiner, Ovetta Wiggins, Martin Weil and Clarence F. Williams contributed to this report.