Snow falling outside

1

I finally made the snow falling work and now I’m trying to “keep it out” . What I mean by that is: imagine yourself in a room looking out the window, watching the snow falling. As of now, is snowing in, in front of the window. I tried to use a mask (above layer) and [COLOR=black][FONT=Verdana]obviously[/FONT][/COLOR] I don’t how because is not working. Please, help.