Thanks, gentlemen, for taking the time to post your comments. The snow is done with what is called a cloning brush, in this case in a small guy's software called Sagelight. In the photo are many bright white areas made with sifted 'snow' soft flake from Woodland Scenics. I place the reference circle for the clone brush somewhere in a white area, then move the brush circle to where I want to create a similar, or variant of, the same effect. I can reduce the 'pressure' of the brush to very low and then swipe the circle across the side of the engine. What you see is how it turned out. You can also make the clone circle very tiny, like a dot, and when I keep the pressure up, it makes brighter, thinner 'steam', as I show coming out of the air pump vent in front of the stack, or the exhaust from the turbo-generator just above the cab.