Hi @thehomme ,
with 4.0, you should set the Weight to 1 and plug that Mix Node into the Scale (but you might need to change the two mixed values, or insert a Math > Multiply Node in between the Mix and the Scale).
Random Walk is best. In this specific case, you could probably also use Random Walk (Skin); the difference between the two is (if I understood it correctly), that the Skin Version takes the Base Color into account and the other (just Random Walk) only uses the Radius. But as snow is basically just white, it shouldn’t make any difference here.
