What I think OP is trying to suggest is the same thing I was thinking about the other day.
A script that randomly switches between "weathers" - certain custom daycycles.
So for instance you would have a few different daycycles
A sunny one which is pretty basic
A cloudy one where maybe the shadows don't pop out so much, to simulate cloudy/lighter levels of light
A rainy one where obviously the daycycle is darker and it is raining
Just to name a couple. The script would randomly blend or switch between the daycycles to simulate the change of weather. I doubt it could blend them together, so you'd probably want some extra daycycles that would fit inbetween the transition of Sunny to Cloudy, Cloudy to Rainy, Sunny to Rainy, Rainy to Cloudy etc.
Similar to Grand Theft Auto's system.
I'm pretty sure people were suggesting this back when Shadows and Shaders first came out, and people started experimenting with the Day/Night cycle system. It might have already been made but I can't remember. It's been a while.