The New Orleans region found itself in the icy grip of a winter storm as night descended Tuesday, with the plummeting temperatures freezing roadways and slowly cutting off the city’s major transportation arteries.

The rapid-fire road closings at dusk and officials’ continued warnings may have come as a surprise to some residents who had seen the day as a slushy fizzle — a snow day without the snow.

But as sprinkles of sleet and freezing rain began increasing late in the day, one by one roads were shut and services suspended.

Officials warned the worst could come overnight as precipitation solidified in temperatures that were expected to dip to 20 or below north of the lake and the mid-20s south of the lake, causing dangerous ice to spread across area roads, especially those that are elevated.

“As everybody knows, two things are going to happen today. It’s going to get colder and it’s going to get wet,” New Orleans Mayor Mitch Landrieu said. “And when it gets colder, and it goes below freezing, that wet is going to turn into ice. And when ice events hit an area that’s not prepared for it, it creates clear and present dangers for people in a number of different ways.”

The warning to avoid icy streets echoed those of other officials throughout the New Orleans area as a state of emergency remained in effect and most government offices and schools remained closed in anticipation of treacherous conditions.

The slow-moving storm was expected to continue dropping freezing rain and sleet throughout the area, as it had throughout the day Tuesday, before perhaps transitioning to snow and then stopping around midnight.

All that precipitation was expected to add up to about a quarter-inch of ice accumulation. Up to an inch of snow was expected as well, though it was unclear how much of that would stick around until morning.

For officials, the primary concern remained the area’s roadways, many of which were shut down Tuesday evening as the freeze set in.

“Until we get all the freezing precipitation off the streets, I would recommend people shelter in place and stay off the roads,” Jefferson Parish President John Young said. “We’re thankful most citizens heeded our advice today.”

Three things served as the focus of most warnings: elevated roadways, bridges and black ice.

Elevated roads and bridges are cooled by air both above and below their surface, meaning they freeze faster than ground-level streets. That fact began having its effect early in the day Tuesday as bridges and Interstate highways began to close.

By evening, a long list of bridges had been closed including both the Lake Pontchartrain Causeway and the Interstate 10 twin spans, largely cutting St. Tammany Parish off from the south shore. Conditions also led to the closure of I-10 from Slidell to Lafayette and other significant roadways as well.

Black ice, or slick patches that aren’t easily seen by motorists, remained a concern on all area roads.

The New Orleans Fire Department stationed equipment and personnel in the Lower 9th Ward and Algiers in case bridges to those areas became impassable.

It wasn’t just motorists who felt the effects of the storm.

Both the Chalmette and Canal Street-Algiers Point ferries were docked by late afternoon after ice formed on the vessels or landings.

Conditions also shut down air travel, and all flights into and out of Louis Armstrong International Airport were canceled Tuesday. No flight service is expected on Wednesday either, Director of Aviation Iftikhar Ahmad said.

Fleeting power outages were reported sporadically throughout the day, but they were fixed within minutes rather than the three- to five-day outages Entergy executives had warned were possible. Still, concern remained over whether ice-covered branches would crash into power lines, or the lines themselves would become overburdened with ice and snap, leading to new outages.

Entergy assembled more than 2,100 restoration workers in the metro area, including 1,000 in Orleans Parish, to respond to any emergencies.

Still, it was a relatively uneventful day for law enforcement patrolling the area’s roads. Seven crashes were reported in St. Tammany Parish by early evening, including two that prompted the closing of the twin-span bridges. None resulted in serious injuries.

In Jefferson Parish, Sheriff’s Office spokesman Col. John Fortunato said no major accidents had been reported during the day. He reiterated that the agency “wants to remind everyone to stay off the roadways and to remain home unless it is absolutely necessary to drive. To reiterate, we will not tolerate folks driving around sightseeing.”

For many, however, Tuesday was a day off from work or school that seemed incongruously quiet given the warnings swirling about.

“The mist! The mist is here!” joked Pat Dehon as he and his wife Maureen stepped out of Fair Grinds Coffeehouse and into the cold wet air just before noon Tuesday.

The Dehons, who live near the Fair Grounds-neighborhood coffee shop, could be forgiven a little sarcasm after 24 hours of warnings, closures and dire media reports about the freeze that was expected to grip the New Orleans metro area and much of the Southeastern United States.

Dehon said the couple hadn’t taken any special measures, other than to invite friends over Tuesday night for a baked-chicken dinner near the fireplace.

But it’s not all joking and levity for the Dehons, who said they would be keeping close tabs on Maureen’s father, who is 97, to make sure he stays warm.

“As long as we have power,” Pat Dehon said, “everybody’s good. That’s our only concern.”

Many residents, however, seemed to be heeding the warnings.

At the Little Miss Muffin children’s clothing store on Old Metairie Road, sales associates Patsy Hendricks and Sara Fogleman bade farewell to the day’s first customer, even though it was already past noon.

Hendricks said the store, which also has a Lakeside location, decided to stay open in case some of the thousands of workers and schoolchildren with the day off wanted to get in some shopping. But by early afternoon it seemed more likely they would be told to close up shop and head home early.

“I think they’re worried about the streets,” Hendricks said of the absent shoppers.

“When the mayor says stay home, you stay home,” Fogleman agreed.

It was a similar scene at the Northshore Square Mall in Slidell. Frances Landor, who manages the Cinnamonster store, said the shopping center had been deserted throughout the day.

“I made a little bit of money — not enough to make it worth opening,’’ she said. After getting trapped by icy roads in Baton Rouge on Friday, she was concerned for her workers and was manning the store on her own.

“I don’t want anyone to be stranded. ... I told my kids, ‘Don’t come in today,’ ’’ she said.

Traffic on I-10 in Jefferson Parish was light but consistent, and it wasn’t difficult to find grocery stores teeming with activity.

John Casady, store manager at Canseco’s, said the store ran all three registers Monday night for four hours straight, describing the scene as similar to hurricane preparation, just less intense.

“People are buying a lot of everything, a lot of food, a lot of beer, a lot of liquor, a lot of soups,” he said. “Also, a lot of deli meats and batteries.”

Staff writers Chad Calder, Sara Pagones, Faimon A. Roberts III and Jaquetta White contributed to this article.