I was browsing through XNA related videos on youtube, like I sometimes do, and came across something really interesting. This guy (not me) made this snow accumulation effect, and it is GOOD!
http://www.youtube.com/watch?v=vtYvNEmmHXE&feature=relatedFrom what I gather, snow accumulates on lighter areas faster than darker areas, and the amount is calculated for each pixel each frame. Pretty clever way of doing it, and great result. Just thought it was something cool worth posting.