--->Steps to follow
[1] Open Map Properties
[2] Use Terrain Fog
[3] Z Start - 10.00
[4] Z End - 5000.00
[5] Global Weather - Wind (Heavy)
[6] Create a new texture of snow - Make it 100% white
[7] Import it to your map then apply the new plain white texture you've created
to your map.
Wa-la you've got your self heaven, no I am not making it for you. But that will give you exactly the results you're looking for. The rest you just add doodads, make units height about 300-500. Just make everything 300-500 height higher. And add pathing blockers.