this is pretty straight forward, i think a slider or value box for the intensity of sunlight would give better control of "weather" on levels, as increasing the already existing cloud coverage or fog density sliders never feels right because, unless you alter the level settings yourself, the sunlight remains just as bright. it's a pretty simple solution to getting the feeling of overcast weather in my opinion. i've attached a pic of derby arena with the fog and cloud density sliders maxed, and the sunsky brightness set to 0.1