I've actually encountered the exact same thing, I was rather confused whether it's an actual weather or whether it's some kind of bug as the same weather happened like 6 times within an hour or two.
Did it really work disabling the prepass skin shader?
How did you disable it ?

Hi! I'm not entirely sure what causes my problem but let me try and explain. Issue : Whenever I move in skyrim outside and/or in city, the light that's suppose to shine down on the ground disappears. Basically the entire map covers itself in a shadow, as if the light source disappears. But whenever ...