Cycles render – Using the Normal Blue channel for top side effects

Software:
Blender 2.8 | Cycles Render

The shading normal‘s Z component can be easily used as a ready-to-use procedural mask for ‘covering effects’ like dust, snow, and if baked, also as a base for particle effects like debris and vegetation.

This simple shading flow example the shading normal‘s Z component, that represents how much the surface is facing upwards is separated , mixed (multiplied) with a noise textured and than fed into a ColorRamp Converter node for fine tuning the resulting mask:

This is the full shading flow of the snow effect in the image above: