Snow

The styrofoam is white, but it does not look like snow.  So I use Woodland Scenics "Soft Flake Snow" (SN 140) and their Scenic Cement. Woodland Scenics' instructions say to spray Scenic Cement onto the desired area, then sprinkle on a thin layer of Snow. Repeat to get the desired thickness of snow.

I have found that the Scenic Sprayer does not work as well as I'd like - it sprays out large and small droplets over a wide area.  The gust of wind that it produces can be disastrous if there are small items in the area. Spraying with an airbrush might work better, but I haven't tried that yet.

For convenience in holding the bottle, pour a little Scenic Cement (about a half-inch deep) into an small bottle (I use an empty yeast bottle.) Add a few drops of something like Ivory dishwashing liquid to make the glue wet the snow better.  Otherwise, much less snow gets glued down. 

Use a paint brush to generously coat the styrofoam to be covered with snow with Scenic Glue and allow it to dry. This seals the surface to help prevent the Scenic Cement from being absorbed into the styrofoam. When dry, apply a generous coat of the "wetter" Scenic Cement. A paint brush works well for roofs, hills or rocky areas, tree limbs, etc. For level areas of Styrofoam use a plastic pipet/eye dropper to apply as much Scenic Cement as you can in order to get as much snow to adhere as possible. Take a pinch of snow from the jar lid and sprinkle it onto the wet surface.  A teaspoon can be used to get snow sprinkled into places inaccessible to your fingers. Repeat as often as needed until no more shiny, wet Cement can be seen.  I usually allow it to dry a day, but maybe I'm allowing more time than really needed.

Nonporous surfaces, like roofs, can be painted with the Scenic Cement wherever you want the snow to stick and then the snow is sprinkled on as before.

When the Cement has had time to dry, remove loose snow  with the nozzle of a a small vacuum cleaner (I use our Dirt Devil.) Don't be surprised when a lot of snow comes up! If more snow is needed (and it probably will be,) wet the area with the Scenic Cement again and sprinkle on more snow.

Be very careful about getting Scenic Cement and/or snow onto the track! It doesn't take much of either to stop or derail your train. After sprinkling snow anywhere near my track I run my index finger between the tracks to remove loose snow and any wayward Cement. Sometimes I moisten the finger with my tongue first to help pick up the snow. Then I run my train around the track. This makes dirty spots pretty obvious. You might want to use an engine that is easy to put back on the track, like the Denver & Rio Grande Western steam engine.