Wow, that's a brilliant idea! So simple, yet so effective! Bungie really should think about it. But well... I don't think that we're the first ones thinking about weather effects and stuff like that. I guess there's two options: 1) due to some internal arguments / reasons they scratched weather effects from their schedules 2) they will implement it with updates post-launch But I think it'll take quite a long time to do so, otherwise they would've put them into the game in the first place