If the snow is powdery, spray water on it with a plant mister. Don't overdo it though. Allow the water to freeze, making a much harder surface than the untreated, powdery snow. Then place the ring around the track. To counteract the heat generated by the plaster, store the powdered plaster outside so that it can be cold when you mix it. Use cold water when mixing it, and make it even colder by tossing in a few fists full of snow. Stir the snow around until the water is really cold, but if it does not all melt, scoop it out. Leaving snow in the plaster will cause air bubbles in the final cast. Once the plaster is mixed, carefully pour it in the ring, but ''do not'' pour it directly in the track. Pour it next to the track and let it flow gently into the track itself. The spot where the plaster is poured will very likely leave an impression in the snow, and you do not want that to overlap the track. The mix may take well over an hour to cure, so you might want to leave it for a day. With any luck, you should have a nice cast of your track, though it is not likely to be a nice as the ones you can cast in mud.
