On top of that and more complex, it'd be nice to have outdoor weather effects translated to interior zones through windows, audio and lighting, as was done in some Oblivion and Morrowind mods.
And, a last point, more a personal opinion: Howling winds.
In Morrowind we could experience a massive thunderstorm with strong winds and a downpour, and we could also experience a small shower. Each was distinct, the small shower didn't have all the loud blowing winds and lightning, it was just a sprinkle, while the storms would have louder howling winds, thunder lightning, ect.
In Oblivion, every time it rains, the winds that accompany it makes you feel like your standing on top the tallest mountain during a tornado. I'd like to see some variation in the weather like we've had in Morrowind.