The Nordic Combined event comprises a ski jump from the normal hill and a 10 kilometre cross country race the same day.
By Saturday afternoon it was raining heavily at the jumping hill and cross country course and the forecast for Sunday was not much better.
"I have done many jumps here but I have never jumped in the rain. It is different," American Todd Lodwick, one of the favourites, said.
Tino Edelmann of Germany said the wet conditions made it harder to take off properly from the jump.
"The track is very wet. The skis are not so good in these conditions," he said.
Lodwick and fellow American Billy Demong dominated last year's world championships and are favoured to win their country's first Olympic medal in Nordic combined.
"I feel that we have improved and can be on top. We know what to do this time," said Lodwick, 33, who is competing in his fifth Winter Olympics.
Other contenders include veteran German Felix Gottwald, who won individual and team gold at the 2006 Games, World Cup leader Jason Lamy Chappuis of France and Magnus Moan of Norway.
"I feel that I have much more improvement inside me," Moan said after a practice jump.
But the forecast for bad weather suits the Japanese fine.
"I expect this to be advantageous for the Japanese team," Yusuke Minato commented, saying the wet conditions were similar to those in his home country. Japan won last year's World Championship team event.
Team mate Norihito Kobayashi identified the United States, Norway, Germany and Austria as Japan's main rivals.
"We're strong enough to compete against these countries. The key thing is not to be stressed," he said.
The competition rules have changed since 2006. Athletes now take one jump from a normal hill as opposed to two and then ski the cross country course the same day. Previously they skied on a 15 km course the second day.
Defending champion Georg Hettich of Germany, who won the equivalent normal hill event in the 2006 Games, is back to defend his title but is languishing 34th in the World Cup standings.