wee! my first post!
I snow based my entire Space Wolves army (well, 1000 points, later to be rebased and expanded to 1500 pts). Green stuff is rolled out in generous portions, and applied onto the base. Even it out, so it has a smooth surface, but irregular at the same time. Stick some small pebbles in it to break up the snow patches.
Paint the snow white, or build it up from a light grey. Paint rocks in whatever fashion you fancy.
Stick your mini on the base.
hey presto! -Snow base.
Later,
-Punk