By Friday midday, Denver's airport had reopened, after a two-day shutdown because of a blizzard, but the damage had been done to flights all over the United States.
Almost 65 million American holiday travelers, a record, are on the move this weekend, reports CBS News correspondent Mark Strassmann.
"It's intense. It's crazy, yeah, very crazy," said traveler Arlene Anarake.
"We survived the hard part. We got all the kids and the luggage checked in," said traveler Jason Arters.
Holiday travel calls for survival skills.
"Bring an MP3 player. Bring a Game Boy for your kids. Bring some food for your knapsack. Be prepared to stand in lines for longer periods," advises one veteran.
The American Automobile Association expects that four out of five travelers — 81 percent — will go by car, but if you are driving, go easy on the holiday cheer. Many states are promising to crack down.
Traveling conditions will be horrible around the Midwest and Great Lakes, not because of any snow but thick fog and rain could create some real headaches around Chicago and Detroit throughout the day, warns CBS News meteorologist George Cullen.
Lines were long Friday morning at Reagan National Airport in Washington, but were moving steadily, reports . Many airports like that one are mini-malls, giving flyers a chance to zip through some stores to grab some last minute gifts.
Relief was in sight Friday for the thousands of travelers stranded at London's Heathrow International airport, when British Airways said it was resuming most of its short haul flights after thick, freezing fog caused four days of cancellations and delays. Britain's Meteorological Office forecast dry air from the south would begin to lift the blanket of fog around the airport by Saturday morning.
As flight after flight was canceled in London and Denver, the situation grew into a logistical horror for fliers, whose vacations were disrupted if not spoiled, and for airlines, who may lose much-needed revenue.
Harmon Burns was at Reagan National Thursday night and came back Friday morning to see if his daughter's flight from snowed-in Denver will get off the ground.
"I've got a backup plan where she's going to go to Utah and fly to Newark and all this other stuff," Burns told Bagnato.
Industry officials said it could take two days to untangle the knot, which is tightest in Denver, wherekept the airport closed two days.
Jodie and Andy Hartfield of Colorado Springs, Colo., spent a sleepless night at the Denver airport with their three young children. Luckily they scrounged a cot and some blankets from a family that left the airport to stay in a hotel. The Hartfields decided to stick around until Christmas Eve in hopes of catching a flight to Seattle.
"We can't go home, the highway's closed," Jodie Hartfield said. "We can't get to the car, it's 10 miles away. And the hotels are not cheap."
"A lot of people are going to lose their holidays," said Joe Brancatelli, who runs a Web site for travelers called JoeSentMe.com. "The smart ones may decide to just stay home."
Inclement weather can make air travel a nightmare under the best of circumstances, and the impact is only magnified around holidays.
But what makes this year's snags so daunting, travel experts said, is that airlines have tightened their belts in recent years to regain financial stability. That means there are fewer employees to help stranded passengers than in years past, and fewer empty seats to offer stranded fliers determined to reach their destinations.
"This is the worst-case scenario," Brancatelli said.
Most Americans heading home from London will eventually make it, as airlines are making long-haul flights a priority, reports CBS News correspondent Elizabeth Palmer. No such luck for those flying domestic. Stranded in waiting rooms — or even in chilly tents — they were being re-routed onto buses and trains.
The gummed-up service in London reverberated across Europe, slowing travel to and from Helsinki, Vienna, Brussels, Paris and Amsterdam. The majority of the cancellations at Heathrow affected British Airways travelers.
Large passenger planes can land using electronics, but reduced visibility means that pilots have difficulty spotting other airplanes, thereby increasing the risk of collision. The need for extra spacing between airplanes means fewer planes can go in and out of the airport.
"It's bedlam," said Nicholas Velez, 23, from Washington, D.C. "The whole terminal is so packed you can barely walk."
With Heathrow hotels so full that even service rooms were occupied, Velez was one of the 500 people who slept in the chilly terminals overnight while waiting to rebook a flight home. Heated tents, sleeping mats and catering stalls were being set up for anxious travelers.
Zubair Qamar, 33, also heading to Washington, was luckier. He was given a hotel voucher after waiting for six hours Wednesday. "I spent some of my vacation in a five-star hotel, which was not so bad," he said. "But I would have preferred to be back."
UAL Corp.'s United, by far the largest carrier in Denver, said that by Thursday afternoon it had canceled more than 2,000 flights system-wide, primarily because Colorado got smacked by the most powerful snowstorm it has seen in several years.
"This blizzard is unprecedented, and it's in our second-largest hub," said United spokesman Jeff Kovick. "It is completely unprecedented for the airport to be closed for two days."