My favorite snow is Sweet N'Low the artificial sweetener. It does not yellow, looks great, is cheap and being artificial does not attract bugs
Apply it by painting a water/white glue mixture in the areas I want covered and simply sprinkling it on. After it dries, I use my air compressor, blow off he excess, and then add more if it needs it. For large snowdrifts, I first use Durhams water putty to build up the drift and sprinkle on the Sweet N Low while it is still wet.
As far as weathering the troops, lightly Dry brushing with white goes a long way. But remember bootsand lower pant leg getmust ofthe contact, unles it is actaully snowing. do not drybrush everthing white.

John Neill
www.johnneill.com