Thanks guys, downloaded the weather mods, read the thread, made a backup copy of scene.dat because I've been "really screwing things up" since my first computer back in 1980.
I also have several zipped backups of the entire game BTW, suspenders and a belt are always a good idea if you don't want your pants to fall down. I'll try the previously made mods first, then see what else I need to do.
I'm running S3D 0.9.9 which apparently does open scene.dat these days, so anyone following this can disregard the disclaimer in the 2007 thread;
It can only be adjusted using mini tweeker right now as S3D dosn't suport it yet.
which no longer applies as it supports it now.