The temperate biome turns into a winter wonderland at higher altitudes!
I added snow features into my vegetation shader. It's just a simple layering of a snow texture on top. Trees, rocks and some objects all get a nice and soft fluffy topping. The amount of snow is adjustable so the transition is gradual as you ascend the mountain, from light patches of snow to fully covered.
But be careful while having fun in the snow... the cold will get to you and then you die. Cold weather mechanics coming next.