immersive weather update

cant find the right Topic. Here's a weather update that would fit Minecraft's vibe perfectly..
If it thunderstorms, then the rain should (rarely) form its own little waterfall down a hill!! And ofcourse fades away after the rain stops. And for the roof part at the entrances of caves, or any hole, the water from the rain slides to the edge slowly and drops down slowly or realistic-speed, and if it thunderstorms, then it drops down harder ^^ If that makes sense?..