Snow landscape

Have a snow landscape with castle. D5 does that very well. The vertical surfaces are of course without snow. The circular forest edge (200m diameter) is 2D and therefore remains without snow and a 3D forest edge seems to me not feasible. How to fix that.

I made the forest edge partly 3D. Is better. Snowfall on photo clearly visible, also on video. But when I make a video with camera movement the snowfall during this movement is minimal to 0. ??? Only with very very slow movement and adjustment of snow parameter the snowfall is visible. And then with a different falling direction depending on the direction of movement.