Welcome timbo, you have picked a particularly difficult terrain type to map. My suggestion is to look at plenty of reference pictures about snowy scenes because were pretty unfamiliar with snow - esp deep snow here. I would also suggest looking at snowscapes done by oil painters and other artists too because somehow they all have to capture the essence of snow. Sometimes snow lacks fiddly detail and shape and relies more on colour and shadowing to get the effect across. It can be hard to do snow in typical pen and ink style. Djekspeks snow on that challenge entry is worth a look cos a few washes of light blue brings out some great shadowing for it that shouts snow quickly.

If your looking at a battle map then thats likely to be top down so looking at snow covered foliage from above is even more unusual for us.

You could try to paint it or you could look at some procedural texturing of 3D terrain. I would point you to Terragen which has a free edition if you can stand the 800x600 limitation. It can do snow real well though I don't know how much effort it is to set it up for that.

http://www.planetside.co.uk

Look through the gallery -> e.g. :

http://www.planetside.co.uk/gallery/...esize.jpg.html