This recent mod by Laast, creator of Pure Waters, pretties up the weather effects in Skyrim and adds new textures and more realistic nights.
According to the developer’s description “Pure Weather adds dozens weathers and lighting variations for every areas in Skyrim, with various sunsets and sunrises, and various rainy and snowy weathers. It uses realistic lighting, colors, and textures to enhance your experience without taking off the lore Skyrims feeling.”
It also promises that if you can run the vanilla game with the HD pack the mod won’t cause a performance hit. That might be great for people with older computers.
You can check it out here: