I've updated this mod with a new default_district.xtbl and with changes to weather.xtbl and skybox_effects.xtbl. Now Steelport's weather should change more frequently, and the effects will be much more varied.
You can get a day/night cycle by installing sandbox+. However, the transition from one time to another is pretty abrupt and noticeable. I tried to smooth it out a bit with the weather effects in this mod, but it's still not perfect. Blame THQ.