No weather effects or anything dynamic in this game. idtech5, or at least its implementation in RAGE is, forces pretty much everything to be completely static. Just about everything is a part of the megatexture. There's no real-time lighting going on here. All of the shadows and lighting effects, etc. are painted on to the textures (it's really jarring to see the real-time NPC shadows mix with environment 'shadows'. The whole thing is just a bunch of smoke and mirrors, really. It lets them achieve 60fps easily, since there are almost no real-time special effects or post-processing going on, but I think the cost is pretty large.
It's kind of like how Myst looked amazing at the time, but when it came down to it, it was really just a bunch of slightly interactive still CG pictures and photographs. idtech5, to me, feels like that concept taken and applied to a 3D environment.