Make the wither storm debris cloud only appear if its have big brain so it can be more realistic and add a lightning bolt rain effect when the wither storm can be seen in the distance by player.

from my experience, forcing rain and thunder gets annoying cough cough engender cough cough

I feel interfering with the weather would be troublesome compatibility wise and almost annoying (I personally find rain a bit frustrating). I don't plan on changing the debris cloud and personally prefer the way it is right now.