Try to think about how it should look where are the hotspots that would leave less snow what kind of shoes a person uses, and how he walks. Then you just start digging into the snow, removing it where needed. For this one I used a dark gray since I won't be digging much so: R:77 G:77 B:77 (Fig.02). It would be wise to study your scene to figure out what will be needed most. In Photoshop you should not begin painting with a white canvas, as you will be unable to have negative displacement, so instead pick a colour that will give you enough leeway in both positive displacement and negative displacement.

Now created an orthographic camera on top of your scene and make a render to use as a guide in Photoshop. Increase the texture size depending on the scale and level of detail you want. Tweaking will be necessary on the second plane I found Z:-0.4 was good for me.

The top one will be the standard ground positioned at Z:0.0, and the second will be just underneath it.

I used centimeters for this one (Fig.01). Always remember to select your scale before starting a new project.

Vray 5 displacement c4d