Making snow&rain "affect" some things?

[Amnesiaplayer]

I am so pissed. I want to make a map, where you find yourself at the middle of the mountains.
There are a lot of "rocks" that are ontop of the "rock you walk on" so basically, what I want is I want that the rain. stops if it touches an entity. I don't mean just disable itself, but it is raining, but if there is a rock underneath, it WON'T rain where it is supposed not to rain.
It's really difficult for me to creaye a realistic looking Trenches, Mountains...
With snow either, I need trenches where it snows etc, but I can't
Is there really no way to make a block box, where the particles CAN'T get in, or something like that..
It completely destroys my whole idea, I'm serious, WHOLE IDEA.
If this is the case, I'm gonna cancel my third game mode, and just stay with the "unrealistic" way on the mountains.

if you are standing on the ground, and there is an umbrella above you, the rain won't get acces, to your head, Since your umbrella is above. and in amnesia, "rain"particle is jsut baddas and just "rains" through everything.
and NO "smart" people out there, don't tell me to place the "rain" particle a little more high, I'm creating trenches, mountains. since those AREN'T planes, it won't work.

if there was only a possability that there is a "rainbox" where you can see "purple" or some other colors just like "technical box" what you can't see In game. that would make it easier to fit some rain shits.
(you can See where you place the rain particles because there is a "box" surrounded where the rain can only spawn.)