Woodland Scenics makes a decent snow, and it's eapecially good in that scale... It has some "sparkle" that makes it look pretty good. Personally, I use baking soda for snow, but Doog have a seizure if I recommend it... I've never had any problems with it, but he has a couple horror stories using it...
I usually paint my celluclay ground and "drifts" with white latex paint, and use the baking soda on folliage and the model(s) and tires/tracks...
Some guys have used flour, but I'd advise against it. It turns yellow and attracts critters unless it's REALLY sealed well... Weevils will get into it and a scale-foot long bug doesn't usually work on a diorama...