Turn off particle effects and it's a even harder to tell, I just delude myself that I ate too much before the battle!
It's the fog that gets me a little more though, because this does happen, player 1 joins, has fog, player 2 joins later, no fog, player 1 can't see anything, player 2 is fine.
That's the only thing I can see wrong with the weather system, rain doesn't effect me too much since I can't see it, I don't know if it's there.