Had to throw the animation away.
Forgot some other things...
But here is a lousy little preview animation. No clouds, no shadows, just to see if it's OK so far. The wet shader's minimum altitude is adjusted in the middle of the animation, that's why it's popping.
It's only slightly more than 2MB, so I didn't post it on Vimeo. I hope the quality is OK for seeing what's going on.