A forecast of better weather means that the worst may finally be over for tens of thousands of air travelers who were grounded by flight cancellations that skyrocketed over the New Year's Day weekend.

January usually means fewer people flying, and that will be even more true in 2022 because many business travelers haven't returned to the skies.

The lighter crowds should buy airlines time to prepare for the next big onslaught, around spring break. That, however, won't help the hundreds of thousands of flyers whose Christmas and New Year's plans were scrambled by airline staffing shortages and wintry weather.

Here's a look at the factors that snarled flights for so many people during holiday season, and what the next few weeks are likely to bring.

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WHAT HAPPENED?

Airlines were prohibited from furloughing employees as a condition of receiving $54 billion in federal pandemic aid from taxpayers. But that didn't stop them from encouraging tens of thousands of workers to quit or take long-term leaves of absence after the pandemic torpedoed travel in 2020.

Airlines that got caught with shortages of pilots, flight attendants and other workers last summer and fall — think Southwest, American, Spirit and Allegiant — thought they had time to beef up for the winter holidays. They went on hiring sprees.

That wasn't enough, though, when the highly contagious omicron variant of COVID-19 struck, knocking out flight crews just as holiday crowds began to pack airports. United and Delta were among the first to get hit just before Christmas, blaming canceled flights on a lack of crew members because of the surging virus.

Then storms packing snow and high winds lashed the Pacific Northwest, the Rockies, the Midwest and finally the mid-Atlantic region, creating waves of cancellations that resembled dominoes falling.

The global spread of omicron meant that widespread flight cancellations weren't limited to the U.S. Airlines in Europe and Australia reported similar problems with crew shortages.

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WHEN WILL THINGS IMPROVE?

Judging from early numbers, Tuesday might prove to be the turning point. After more than 3,200 U.S. flight cancellations on Monday, the number for Tuesday was down to 1,400 at midday — better, although still very high. A storm that crippled Reagan National Airport outside Washington, D.C., and Baltimore/Washington International the day before had moved on, although there were residual cancellations because planes weren't able to get into those airports sooner.

Airlines should get a break, with January and February usually being slow months for travel. Willis Orlando, senior flight expert at Scott's Cheap Flights, said airlines should have more ability to trim routes, reassign pilots and tap reserve staff. JetBlue has already reduced its schedule until mid-January and possibly longer.

Also, airline crews can return to work sooner after catching the coronavirus. Last week, U.S. health officials changed their guidance and cut in half — to five days — the time they recommend that people should quarantine if they catch the virus but have no symptoms. Delta and JetBlue had lobbied for the change, although the largest flight attendants' union criticized the move, saying it compromised the health of cabin crews.

On the negative side, new cases of COVID-19 are continuing to mushroom in the U.S., Canada, Australia and much of Europe. The seven-day rolling average for daily new cases in the U.S. has more than tripled over the past two weeks, to 480,000 on Monday, according to figures from Johns Hopkins University.

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SHOULD AIRLINES HAVE HAD MORE STAFF?

Although Congress did forbid airlines from laying off workers, lawmakers did nothing to prevent the large-scale staffing cuts that airlines made by paying people incentives to quit after travel collapsed in early 2020.

That left airlines short-staffed when travel recovered more quickly than expected during summer 2021. It takes time to retrain pilots and bring them back from long-term leave. Compounding the labor shortage, airlines like Southwest and American added flights to bring in more revenue.

Kurt Ebenhoch, an airline-consumer advocate and former airline employee, says travelers would still be seeing canceled flights now even if carriers had avoided those mistakes, "but not in this high of a number."

"Why did Southwest, American and Spirit run into such terrible operational problems and Delta, United and others did not?" Ebenhoch says. "The difference was in management decisions .... (C)arriers that were more aggressive in resuming their schedule, getting closer to pre-COVID capacity faster and left little margin for error in their schedules experienced more operational problems, and their customers suffered."

Airlines are trying to match staffing levels to passenger numbers, and travel has not fully recovered as the pandemic drags on. In December, the number of people going through airport checkpoints in the U.S. was 16% lower than during the same month of 2019.

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IS THIS RUN OF CANCELLATIONS UNUSUAL?

Bad weather — from winter blizzards to summer thunderstorms — can always snarl air travel. So can technology outages and other hiccups. And that risk grows during the holidays, when more people are flying. The holiday season in late 2013 was a particularly painful one for travelers, with airlines canceling about 10,000 flights — and that was long before anyone had heard of COVID-19.

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COULD THE AIRLINES HAVE PREVENTED THIS?

Even critics of the industry give the airlines some slack, noting that scope and speed of omicron's spread was a shock to just about everyone. Other industries were also affected by employees contracting the virus and needing to isolate.

Paul Hudson, president of the consumer-advocacy group FlyersRights.org, said airlines should have planned better and the federal Transportation Department should have required the airlines to have ready reserves of people and equipment, "but the omicron variant high infection rate is primarily to blame in the holiday season disruptions.''

The airlines have been hiring. According to the latest figures from the Transportation Department, U.S. passenger airlines employed the equivalent of about 409,000 full-time workers in October. That was down nearly 10% from the same month in 2019, before the pandemic, but up more than 43,000 jobs, or 12%, from October 2020.