The biggest confrontation of the 2012 Summer Games won’t come between Michael Phelps and Ryan Lochte in the Olympic swimming competition, or Jordyn Wieber and Gabby Douglas in gymnastics — at least not in the mind of London Games meteorologist Robin Thwaytes.

The best competition at the 17-day Games could be between competing airstreams.

“We’re in this battleground between air masses,” Thwaytes said. “They both win on different occasions.”

The city of unpredictable and ever-changing weather has offered two distinct varieties in the past two weeks.

“We’ve gone from shivering to sweating in a week,” said Douglas Charko, the meteorologist for the U.S. sailing team who compiled a report on London’s weather for the Canadian Olympic Committee.

Thwaytes and Charko cannot say for sure whether the 17-day Games will enjoy more of the cloudless skies, summer heat and soaking humidity of the past few days, when temperatures hit the high 80s, or the bleak, soggy, chilliness that dominated June and most of July, the wettest on record in London with daily temperatures peaking in the 60s.

On Friday, the day of the Opening Ceremonies, both extremes might make an appearance. The unseasonably warm weather of the past week should be nudged out by a colder, rainier front that will push temperatures to the low 60s by Sunday and which could dampen the nearly 10,000 athletes who will parade into the Olympic Stadium by 9 p.m. local time.

Or, Thwaytes said, maybe not.

“There’s every chance the Opening Ceremonies could go on in very dry conditions,” he said.

Swin Cash, a member of Team USA’s women’s basketball team, did not appreciate being sweat-soaked during the Opening Ceremonies at the sweltering 2004 Summer Games in Athens, but, she said, she disdains the cold and worries about the rain. She visited London in April as a U.S. sports envoy and recalled being disconcerted by both the weather and the varieties of it.

“Oh my God, this was Seattle times 10,” she said. “It would be rainy and cold, and then stop for a while and be nice. The weather felt schizophrenic.”

When she received the white skirt that is part of Team USA’s Opening Ceremonies uniform for U.S women, she inquired whether a nice pair of white pants would be an acceptable substitute. The answer was no. She then asked if there might be some sort of purse so she could stuff something warm inside to smuggle into the stadium. That was also a no.

Mostly, though, she said, she’s worried about rain.

“If I get my hair wet, it’s going to be poofy the next day, and we’re playing a game,” Cash said. “Women think of these things.”

Mariel Zagunis, an Olympic champion in fencing who was selected to carry the U.S. flag, said she had bigger concerns than worrying about what the rain might do to her hair.

“If it rains, it rains,” Zagunis said. “I’m just going to focus on not tripping and not letting the flag touch the ground.”

Thwaytes, one of a team of 16 meteorologists contracted by London organizers to keep athletes and officials informed on weather conditions, said he expected cooler, bleaker weather through next Tuesday, with at least one rainy day in the bunch.

“It’s looking a bit mixed but on the whole . . . not bad,” he said. “Certainly nothing compared to what we had in early June and July.”

That’s when London got a record-setting deluge, caused when the jetstream that typically tends to migrate north in the summer mysteriously camped over Britain. Thwaytes said the chilly maritime weather from the Atlantic Ocean does battle for prominence with the warmer, brighter, continental effect from the east.

The last two Summer Games, 2004 in Athens and 2008 in Beijing, were characterized by such oppressive heat that the U.S. Olympic Committee took preemptive measures, such as having cooling vests provided to marathon runners to wear before their races, to lower their body temperatures so they could stave off overheating.

The USOC took no such dramatic precautions this time around, according to Alan Ashley, the organization’s chief of sport performance, though thanks to a rule change regarding attire, beach volleyball players may now wear leggings and long sleeves if they wish.

Athletes have “really had a chance to experiment competing in London,” Ashley said. “I think that’s actually the best possible way to do the preparation. They’ve competed in all sorts of different environments. London just presents another opportunity for them to make a few adjustments here or there.”

Jamaican star Usain Bolt shrugged off the possibility of bleaker days ahead.

“Personally my coach has warned me: Don’t get caught up with the sun,” Bolt said. “We know London, and anything is possible. I think I can speak for a lot of athletes: We’ve been through the rain, the sun, the cold and everything throughout Europe. I don’t think it will be that big of a problem. I think we should have that covered.”

Rick Maese contributed to this report.