Winter prepared to take a swipe at the Washington region early Wednesday, shouldering its way between a pair of springlike days to deliver what was expected to be a swift, intense snowfall unlike any storm this season.

Along with temperatures predicted to hang right around the freezing mark through much of the day, the snow was expected to fall with a heavy wetness that could cave in roofs and bring tree limbs crashing onto power lines.

As of 11 p.m. Tuesday, the Washington Post’s Capital Weather Gang had increased the amounts of snow it expected to fall, predicting that five to 10 inches could come down inside the Capital Beltway, with more in Fairfax County and to the west.

By early Wednesday, snow had moved northeast into Fairfax County. The Office of Personnel Management decided shortly before 4 a.m. to close all federal offices in the D.C. area for the day. Major school systems — the District of Columbia and Alexandria, and Arlington, Fauquier, Fairfax and Prince William counties in Virginia, and Montgomery and Prince George’s County in Maryland — announced that they would be closed Wednesday. Arlington County government offices and courts are also closed. (Find more closings here.)

Airlines canceled hundreds of flights even before the first flake fell, and air travel in the region figured to be snarled for at least a couple of days. Business gatherings were cut short so people could fly home Tuesday, and many meetings scheduled for Wednesday were called off over concern that no one could fly in to attend.

How can it snow so much when it's not freezing?

Metro canceled its paratransit service and cautioned that there might be delays in bus and rail service if the storm’s worst-case scenario plays out.

That winter’s days seemed numbered was foretold by the high temperatures predicted for Thursday and the days to follow: 45, 47, 53, 57, 58, 55, 58, 63. This big snowfall would not lie around for days, like the massive storms two years ago, and its true threat may be in flooding by the weekend.

It could be the worst winter weather to wax the Washington region since the onset of an era when snowstorms are elevated to the stature of hurricanes and given names.

The people charged with making snow go away urged people not to drive until the roads are passable.

“Let our crews clear the roads,” said Branco Vlacich of the Virginia Department of Transportation, which sent out 4,000 salt trucks and plows in Northern Virginia. “Roads likely will be treacherous at times.”

In the District, clear sidewalks also were a priority.

“We urge commercial and residential property owners to clear their sidewalks of snow within 24 hours after the storm ends,” said William O. Howland Jr., director of the D.C. Department of Public Works. “We need property owners to handle the sidewalks so pedestrians can travel safely.”

Even as the region enjoyed temperatures close to 50 degrees on a sunny Tuesday, airlines were busy canceling flights at the major airports — Reagan National, Dulles International and Baltimore-Washington International Marshall.

Pepco, which delivers power to 778,000 customers in the District and neighboring parts of Maryland, said it had extra line and tree crews working and 450 overhead line contractors available if needed. Additional contractor support and 250 mutual-assistance crews were requested from utility companies in other states.

Baltimore Gas and Electric Co. said it mobilized 1,750 storm and field personnel, including out-of-state mutual-assistance crews.

At Dominion Virginia Power, executives said they had activated a new system that makes it easier for customers to report and check the status of power outages by computer or cellphone.

Much like a hurricane, the storm was too big to sneak up on anybody. It left a notable calling card through the Midwest early Tuesday as it headed toward the Atlantic, but it was just more winter for the middle part of the country.

Before the storm, it appeared that the region had escaped the winter’s worst, but many still pined for more warmth.

As birds chirped in nearby trees in downtown Washington, Rhona Alexander, 58, of Springfield said she was ready for spring.

“I am tired of the cold weather,” she said, stuffing her hands in the pockets of her black winter parka. “I want to get rid of coats and bring out the spring dresses.”

Some folks were not so convinced that the big snow would happen. So they said let’s not get too excited.

“Washingtonians need to not overreact,” said Jennifer Babson, a South Florida resident who grew up in the District and is visiting friends and relatives this week. “You can’t always trust the weather report. It is a lot of hype.”

She and a friend, Bill Fletcher of Adams Morgan, bought bird feed Tuesday at Logan Hardware, where workers warned that the shovels, sleds and snow wipers were going quickly.

Babson and Fletcher said they didn’t need any of that.

“We are not worried. It is going to be 50 degrees on Saturday!” Fletcher said.

In Virginia, the storm was expected to provide the first real test of snow removal from the 495 Express Lanes. VDOT now has specialized trucks that spray anti-icing treatment between the white bollards on the right side of the express lanes. Also, the plowing style is a bit different: The plow trains on the regular lanes push the snow to the right, where the shoulder is. The plow trains on the express lanes will push the snow to the left, onto the express lanes’ shoulder.

VDOT clears 17,679 lane miles in Fairfax, Loudoun, Prince William and Arlington counties. It has a snow-removal program for high-volume roads including Interstates 66, 95, 395 and 495; Routes 1, 7, 15, 28 and 50; the Fairfax County Parkway; the Prince William Parkway; and another snow-removal program for main thoroughfares in neighborhoods, residential streets and cul-de-sacs.

VDOT said crews work on high-volume roads and in subdivisions concurrently. Roads with the highest traffic volumes in each category are cleared first.

The Maryland Transit Administration warned travelers that ice or downed trees could create delays on rail lines. The agency could limit some or all of its bus, rail and light-rail service if snow and icing become too severe.

In Maryland, crews had pretreated major roads and arteries with salt brine. The state has 330,000 tons of salt ready and waiting.

The Maryland State Highway Administration said six heavy-duty tow trucks were deployed to be ready to move disabled tractor-trailers from interstates. Drivers were warned to watch for dark traffic signals and to treat intersections without power as four-way stops.

Prince George’s County sent out 240 vehicles and 300 employees who would work 12-hour shifts until the more than 1,900 miles of county-maintained roads are clear, county officials said Tuesday.

The storm was expected to be the first test for the District’s $4.5 million worth of new snow-removal equipment, including plows equipped with GPS tracking.

Metro said it had 600 pieces of snow equipment ready for cleaning walkways, platforms, parking lots and garages. Metro trains can operate aboveground in snow conditions if accumulation is less than eight inches. If it’s more than that, Metro officials said, the transit agency has to consider whether to suspend aboveground service.

In snow conditions, buses take alternative routes if there are hills, curves or narrow streets along the normal routes.

Marshall Keys, 56, a musician who lives in Northwest Washington, left Logan Hardware on Tuesday with a pair of gloves, a snow wiper, pet-friendly salt and a sled.

With a case of wine and food at home, Keys was set for what he said could be two fun snow days and some sliding at Fort Reno Park in Upper Northwest.

“This one is big enough for both of our behinds,” said Keys, holding his new circular, orange sled. Last time it snowed, he and his wife had not been prepared, so they used a serving tray as a sled. “I am way past this,” he added, “but if it snows, I am going to be ready.”

Mark Berman, Mike DeBonis, Dana Hedgpeth, Joe Stephens, Miranda S. Spivack and Martin Weil contributed to this report.