New command /pw sit tells you situation (weather type) in every region
New configuration node "region-type.<world name>" lets you set region type for world with name <world name>. <world name> is supposed to be replaced with name of your world of course.
You need to set use-biome-weather to true in your config file.
Updated help
If you define a weather and then undefine it somehow, you can get into trouble
weathers.yml sometimes isn't generated properly (has size of 0 bytes)
Region system not fully reliable! (this is fixed in 1.0a)