You could also check out the excellent Sky Pack download by 6e66o. In Google search for " rF Sky Pack by 6e66o ". This pack contains overcast skies, amongst others.
I sent a link the other day for 6e66o's Skybox pack via PM to you.
Just in case you didnt get it, here it is again; http://www.mediafire.com/file/kykgo4w1k486zo1/rF_Sky_Pack_by_6e66o.rar
He did publish it somewhere for public use somewhere but I cant remember where....
Let me know when you get it & I'll shut the link again....
When you find one you want to use, drop it on your skybox file- worked a treat for me & they are truelly beautiful!
Just remember to give him credit in your 'Read Me'.
Enjoy, BLeeK