I know you can't really control the snow but try holding an umbrella over your model next time. Make sure not to let it cast a shadow in the photo, but if done correctly it takes away the amount of snow on her cloths. For some reason this makes it look more like snow and less like dandruff. I know logically is makes no sense, seeing as snow does fall our cloths in real life but it helps. Try it once or twice and see if it works for you or not. Just a friendly suggestion though, it doesn't work for all my friends.