There is a file (or will create when you load the track for first time) ".wet" for each track in your Userdata/Player/Settings... for example MALAYSIAN_GPs.wet for malaysian_GP layout.
You can setup the weather from here to be able to have differents kinds of weather for each track..
I think also you can setup one to one from teh dedicated console..
this line on the file player.plr should looks like this..
MULTI Weather="5" // 0=sun, 1=clouds, 2=rain, 3=default, 4=random, 5=scripted
But i dont know why... always autochange to value MULTI Weather="4"