I play BFBC2 on Ps3, so I'm not sure if the weather can be controlled by the host. But I think it's more likely that the weather is dynamic like so many other games. It will change over the course of the match and isn't always the same.
I think it's more of a thing where different parts of the map are harder to see than others.
e.g. the bases on Atacama Desert are fairly easy to see in, but run out into the middle of the desert and try to snipe someone. Or try to snipe someone when you're at A and they're at B, it's pretty damn hard to see, especially if they're in the back (ocean side) of the ship.