Until the weather turned Sunday, airlines celebrated a long Thanksgiving travel period of smooth sailing.

Even as delays mounted on the busiest day for air travel since the start of the pandemic, the number of canceled flights remained low, leaving carriers with bragging rights — especially compared to chaotic holiday weekends earlier in the year.

Experts say that’s good news for the upcoming winter holiday travel season, especially considering the repeat failures over summer holidays that saw thousands of flights canceled during long weekends.

Between Nov. 20 and Sunday, just 695 U.S. flights were canceled, a 0.4 percent cancellation rate, according to flight-tracking site FlightAware. In an email, spokeswoman Kathleen Bangs called that “quite low compared with pre-pandemic years,” and on par with last year’s Thanksgiving stretch. By late Monday afternoon, another 81 flights within, into or out of the United States had been canceled.

Even Transportation Secretary Pete Buttigieg, who repeatedly took airlines to task for flight disruptions over the summer, gave this holiday weekend a passing grade.

“Yesterday was the busiest travel day of Thanksgiving air travel, and the system did well,” he wrote in a tweet Monday morning.

The Transportation Security Administration screened more than 2.56 million passengers at checkpoints Sunday, the highest volume since the pandemic began, TSA spokesperson Lisa Farbstein tweeted on Monday. The record was not much higher than the previous pandemic-era high, 2.49 million, set on July 1.

Delays mounted Sunday, topping 6,900 that day alone, amid widespread rainstorms on the East Coast, Great Lakes and Ohio Valley and snow in the Pacific Northwest. For the entire week, airlines reported more than 34,000 delays, or about 18 percent of flights.

Still, Bangs called the number of cancellations “exceptionally low — a big win for the industry after a somewhat hectic summer!”

Delta Air Lines said its main carrier and Delta Connection had only 15 cancellations between Nov. 20 and Sunday, with none Sunday despite bad weather and air-traffic control delays in the Northeast.

United Airlines spokeswoman Leslie Scott said this year was the second-best on-time Thanksgiving travel period, and the airline’s third-busiest. Between Monday of last week and Sunday, major United hubs saw low numbers of cancellations, including just one each at Chicago O’Hare and Dulles International. On Sunday, 80 percent of the flights for the carrier and its regional partners arrived on time despite the weather, she said.

And Southwest Airlines said its flight completion factor was greater than 99 percent over Thanksgiving week.

Mike Boyd, president of the aviation consulting firm Boyd Group International, said Thanksgiving travel went more smoothly because airlines have adjusted their schedules and staffing to avoid cascading effects across their network when issues come up at a single airport.

“The real Achilles’ heel of airlines still today is the ability to recoup when there is a major event because we don’t have a lot of extra staffing,” Boyd said. “That Achilles’ heel is still there, but they’re working through it.”

Still, to avoid the meltdowns of the summer, they needed a little bit of help from Mother Nature — no major weather disruptions cropped up at top hub airports this Thanksgiving, Boyd said.

“Somewhere in scripture, there is a biblical requirement that if there’s gonna be a thunderstorm or a snowstorm, it’ll be over Chicago O’Hare during the Thanksgiving holiday. We didn’t have it this year,” he said.

Robert W. Mann, an airline industry analyst and consultant, said in an email that good weather during the holiday travel period, and earlier in the month, was “the gift that keeps on giving, to airlines, their employees, and customers.”

He said airlines also had time to build their staffing levels, and pointed out that some offered premiums to work over the holiday, which helped ensure that there were enough people on hand to work extra shifts.

Mann said a more flexible work environment also helped to “flatten demand toward shoulder periods over the 10 days, which was also the result of fewer flights and seats and higher prices all spilling demand from peak days.”

Boyd noted holiday travel is less of a peak now because demand for air travel is so high year-round. While most flights used to take off with 60 percent of seats filled, flights today are averaging around 90 percent full.

He predicted travel demand may fall slightly with inflation and less pent-up demand from the pandemic, and airlines will continue to be conservative with their schedules and staffing ahead of the holiday travel period.

“As long as the weather cooperates, I think we’re going to be okay for the Christmas holiday,” he said.