Ola Matt
Well I have done something like that a while ago. The dio never got finished because I had another (read better idea with two of the three figures I had for the one in the link I post here. Look at step 9 under the pic is a short explanation how I made it.
SNOWBALL!!! Start of a Dio I hope it is of some use for you.
You could add some satin varnish to it but I should be
very carefull with that as even fresh mud doesn`t shine. Otherwise fresh mud looks kinda like every other groundsurface. It doesn`t run or whatever. As long as it is not disturbed it will be flat. the difference can easily be seen when you tear up the surface as that happens easier to a muddy surface.
Snow can easily be done with Babypowder fixed with Hairspray. an example can be found here:
Distraction Greta`s Revenge On the last page is told how the snow works
I hope you can do something with this information
Looking forward to your work