world space masked decals - only draw decal on 1 surface orientation

hey guys

bit of a long winded explanation but here goes… is there any way to tell decals to appriciate the world Z only - lets say to use as a lerp to put snow on top of an object its touching but not to draw on sides or underneith

with a normal material this is pretty easy to do and has multiple solutions to a fairly easy problem, however with a decal the way that it draws around and over the surface basically from what i can tell - im not sure if this is even possible?

to say this is another way - is there a way to get decals only to draw on the surfaces facing up?

Any answer regarding this topic ?