There's many weather mods out there - and some very good ones - but none really satisfied me, so I've decide to make my own.
WoW stands for "With or Without PP filter" !
That is, it looks very good even on machines where every frame counts...
The PP filters provides are optionnal; the first is a quick copy-and-paste-then-adapt-to-my-needs from the "Natural Graphics Mod" made by ears1991. I've only made little changes to make the sun even more natural (to my eyes, at least) and eat less fps. So, it may not be the best looking PP ever...
Additionnaly, you'll find two other filters wich are more resources hungry.
I recommand the use of the clouds found in ears1991's "Natural Graphics Mod": http://www.racedepartment.com/downloads/natural-graphics-mod.4551/