>>151797060
A lot of their work takes place in a gym, they can do that anytime. Not necessarily only lifting weights, but certain exercises, for example plyometrics. And if necessary, they can either also train some stuff in indoor ski halls or still in the mountains. They don't go completely snow-free in summer, and you can travel to a different place where there is enough snow if you really need that. They will also incorporate other sports to help them build/maintain stamina and certain move sets. Mostly swimming, cycling, and running - especially trail running
Their training doesn't really change that much overall, even though their access to slopes isn't quite the same. They can still use them for the most part. But they will often switch things up a bit and focus on different stuff in the offseason
Depending on the exact event, snow isn't even THAT important. Ski jumping for example can theoretically also take place in summer. And the biathlon and ski long distance guys will train on roller skates, which isn't 100% the same, but very close.