well, this can be late, but just in case.
This works under 146 and 175, i use it in almost all of my MP missions. (hope you don't mind spanish. tiempo = time, clima = overcast, niebla = fog)
This' ll make ramdom weather, fog and overcast.
I also have a script with random objetives for MP missions, just tell me if you need em. Hope this helps you out.
Don't fotget to put the "server" Logic.
?!(local Server): goto "cliente"
tiempo = random 23
clima = random 1
niebla = random 1
publicvariable "tiempo"
publicvariable "clima"
publicvariable "niebla"
#cliente
~5
skiptime tiempo
0 setovercast clima
0 setfog niebla
setViewDistance 1000
exit
PS: I use a fade of 6 sec. to make the changes "invisible"