This was my entry for the Animation Academy Contest a few years back

This was modeled using Blender 2.69 and rendered with Cycles.

There are a few problems with the particle system and the way it animated, but overall I was pleased with the results and learned a lot making it.
Here is a link to the completed animation I made:
https://www.youtube.com/watch?v=zstQ5rATxvQ

I followed the excellent tutorial by Pigart for making the trees:
https://www.youtube.com/watch?v=rtO9maU709k

I could not remember where I got the sky image so I inserted a new one that is creative commons non attribution.