Well, snowcrystals are reflective. On a snowscape, with the sun shining, you have molten snow, frozen again and so on.
Images of white snow should show an overcast sky, at a sunny day, the snow reflects the blue sky.
I do not know how many surface-shaders you use, if one, just add a 'reflective shader" as a child. Take care to keep the reflection softness at zero, else the rendertime is exploding..
With more than one snow-shader, the reflective shader should be the first child.
Volker