Lucy Wallace, a recent transplant from San Diego, had been warned about the bone-chilling winters of her new hometown, Minneapolis. She bought a $900 winter coat, two pairs of boots and metal spikes to make her running shoes usable on icy sidewalks.

So she was at once befuddled and relieved by the record-breaking warm temperatures that made for a rare snowless winter holiday week in much of the upper Midwest.

“I spent hundreds of dollars on a new wardrobe and winter gear that so far has gone totally unused,” said Ms. Wallace, 35, who ran five miles on Christmas Day wearing a T-shirt. “Here I am wearing my San Diego wardrobe in December in Minneapolis.”

A high of 54 degrees made this Christmas Day the warmest on record in the Minneapolis area, according to the National Weather Service. Across much of the region, people contended with a string of days heading into the new year that felt like a mild autumn. Ice fishing was particularly perilous on lakes covered by thin ice caps.

And a hack to host large holiday gatherings was foiled. “Thinking of all the Minnesota families who rely on using the porch as an extra freezer during Christmas entertaining when it’s almost 50 degrees outside,” Peggy Flanagan, Minnesota’s lieutenant governor, wrote on Threads.

It is not unprecedented to have a warm or snowless Christmas in Minnesota. But such days are likely to become increasingly common because of climate change, said Jessica Hellmann, director of the Institute on the Environment at the University of Minnesota.

“It’s a big cultural shift to experience 50 yesterday and how disorienting that is from a geographic perspective,” Dr. Hellmann said in an interview on Tuesday. “It’s a visceral feeling of what climate change looks and feels like for people who are accustomed to living in a particular climate.”

In northern Minnesota, emergency personnel have warned people to stay off lakes, which are covered by an unusually thin layer of ice.

Last week, a Cessna plane that landed on Upper Red Lake broke through the ice, according to Jason Riggs, the Beltrami County sheriff.

“Upon landing, the absence of snow resulted in the plane having difficulty slowing down,” he said in a statement. “Eventually the plane slid into an area of thin ice and the nose of the plane broke through into open water.”

The plane’s two occupants, who had flown from Michigan for a day of ice fishing, were rescued.

In nearby Becker County, a 67-year-old man was found dead on Saturday after his ATV cracked through thin ice, according to the Becker County Sheriff’s Office.

Ted Bonde, the president of the Wisconsin Interscholastic Fishing Association, said ice-fishing competitions in much of the state had been pushed back at least a week as wintertime anglers waited impatiently for the cold to set in.

“I know nature is doing this and it’s going to turn around at some point; it’s just a matter of time,” Mr. Bonde said, adding, “Once it happens, there’s going to be a mad rush to get out there.”

Mr. Bonde, who coaches the high school fishing team in Kiel, Wis., about 45 miles south of Green Bay, said that on Dec. 10, there were three inches of ice — enough to walk on — in his area. No longer.

“It’s all gone,” he said. “Everybody is getting their boats back out where there used to be ice.”

Milwaukee, which has recorded seven days above 50 degrees so far this month, is on track for its warmest December and its warmest year on record, according to Cameron Miller, a meteorologist at the National Weather Service in Milwaukee.

On Christmas Day, the high was 52 — far above the average high of 34 — and it only dipped down overnight to 48, the warmest low temperature on record for the date, Mr. Miller said.

With “only a trace” of snow this month, it has not been an ideal season for winter sports. “I am an avid cross-country skier, and this kind of weather is abysmal for someone like me,” Mr. Miller said.

Jacob Frey, the mayor of Minneapolis, said he had enjoyed taking his daughter to the playground in late December, a month later than in years past. An avid runner, he has appreciated the absence of snow and ice on trails and sidewalks. But there is something deeply unsettling about his first snowless Christmas in Minneapolis, said Mr. Frey, who has made fighting climate change a priority.

“Any enjoyment of the warmth is overshadowed by concern for what’s going on,” Mr. Frey said. “It’s a very eerie and disconcerting kind of enjoyment because it makes you wonder what’s yet to come.”

The unseasonable warmth was expected to shift east on Tuesday and Wednesday, with high temperatures climbing 10 to 20 degrees above normal from the Upper Midwest across the Great Lakes, according to the National Weather Service. Mild temperatures were also forecast along the East Coast, with highs in the 50s in the Mid-Atlantic and temperatures in the 60s in the Carolinas.

Scientists say it is hard to attribute a single anomalous weather event to climate change. But there is no doubt that winters in the United States have become milder in recent years.

Also among the casualties of this year’s balmy winter is the Minnesota Ice Festival, which features a giant maze of ice and snow. It was canceled last week.

“The weather hasn’t cooperated, and we won’t be able to deliver the experience we had hoped for,” Robbie Harrell, the chief executive of Minnesota Ice, said in a statement.

One upside of this strange winter is the absence of a particular type of constituent complaint that starts as early as November, Mr. Frey said.

“We are super proud of our record low in snow plowing complaints,” he joked. “Our plow drivers have been so fast and effective; they’ve been trying out a new strategy and it’s clearly working.”

John Keefe contributed reporting.