As I think the weather plays a huge part in Skyrim... as in adds to the atmosphere etc, I have several weather mods installed. A mod I would like to see could be quite tricky to do. I would like to see storms in the distance, say you're standing at the main gates of Whiterun and watching a storm over the distant mountains, with intra-cloud lightning and rumbles of thunder. To me, that would add a more realistic feel to the game.

God, how many weather mods do you have installed and which ones? Project Reality is fantastic IMO.