You know Quake 1 sky is not supporting full weather system, changeable time of day. Material in quake is really simple uses two mixed textures that moving in some direction and it is all.
If you need same material as in Quake 1 i can create it for you 
but integrating second layer into Fast Stylied Procedular Sky is little more complicated than this.
I have to to care about lighting, parameters of second layer, covering the sun, UV coordinates on sphere, horizon fade ect.
It is possible but it would make my material messy as hell (hard to extend) and noticeably slower.
Anyway I will try to add this functionality as an optional second layer with same parameters base layer :>