Drifting snow

i did a search and couldn’t find a post that matched my question. =/

i’m new to flash and i trying the snow tutorial from here and everything worked fine except my snow did not drift slowly side to side like the example on the page. the only thing i edited in the action script was the document size. how can i make the snow drift?

also would anyone be able to refer me to a post or tutorial on how to make the snow pile up?

please and thank you!

(-: