Thank you and merci beaucoup! I agree that the snow looks a bit grey, but I decided not to use a completely white colour for the snow, because it looked kind of washed out. Additionally the conversion of a QT with best animation (codec) settings to a H264 to make the file much smaller creates some kind of a low contrast.
I wish I could have rendered this one with higher quality settings, but as you can imagine, renderings with this amount of clouds take veeeery long to render, and since I don't have a killer computer I decided to reduce the quality settings a bit.
AND I'd love to animate the trees, so that they are bent by the snow wall!!!!! But I didn't succeed so far. Maybe next time...