I have fantasized about it though, at least the rain part. Getting hot and ready out in the backyard during a warm Miami rain shower would be lovely. The closest I've gotten to this is making out at an abandoned zoo and cuddling in a nature preserve.
I haven't give the snow version of it the slightest thought before. Are we talking with or without clothing?
I have been out in the snow in swimming trunks before, after spending time in a sauna, which was oddly fun. I imagine having post-sauna, naked snow sex can be fun, as well as otherwise fully-clothed snow sex (where the only parts of the body really touching would be the sexual ones).