I've done a search and found snow globe worked better however they all show something bought inside but my dd needs to do it for a competition at school they suggested a snow scene and she chose this. Ive thought of using white tac to create a snowman would salt dough work.

http://www.yourfamily.org.uk/family_fun/days_in/make_it/make_your_own_snow_globe

This one suggested glycerin do you think we need that.

glyciern (sp?) slows the snow down therefore a more snowy snowstorm. for the inside you could always use plasic cake decorations, not sure if dough would stay hard, would it be the one you bake?

I agree with jellytot about the glycerin, what about using plastercene(sp) or that other modeling clay not sure if its called Fimo