Changes the weather chances for the RegionID. Used to get rid of, or add weathers to an area permanently. The values must add up to 100 or you will get odd results.
At least with Bloodmoon, all arguments except the first seem to be optional. I am not sure if this remains true with Morrowind and Tribunal.
If you want to maintain compatibility with a Morrowind only install, it would be best to use only 8 arguments.
