A little help on snowfall method!

I used the snow fall method (FROM THIS SITE) to make a scene with snow falling and fog.
the problem is that if I make the fog flow, then the snow fall restarts after last frame of fog (clouds layer).
but I want to make snow fall continuous.
can anyone help?

here is the scene- (http://www.yourfilelink.com/get.php?fid=216515)
pass- Gurpinder Singh.