When playing with regular vsync, i.e. fps locked at 60 on my 60hz lcd, I did notice odd weather behaviour such as clouds coming and going in a matter of seconds.
As I said, might be pure coincidence, but playing at half vsync gave me more realistic weather conditions with no awkward and sudden changes.
Will have to play a bit more to confirm.
If it's a bug, it's a nasty one indeed and I'm afraid it might not be easy for Rstar to fix; having to play at 30fps kind of defeats the whole purpose of RDR2 on pc