Skyfall Lake is remarkable place. The lake itself is at 1150 meters elevation and is about 17 km long and 10 km wide, nestled beneath 2200 meter high Black Dragon Mountain. To the west of the lake is an 8 km wide belt of marshlands.
Above the lake is a perpetual rainstorm, a waterfall from the Sky River. Monsters, treasures, and other entities from the Celestial Realm are known to fall down occasionally into the lake, where trolls try to fish or dredge them out.
The lake is incredibly deep. Far deeper than our Lake Baikal, and in places bottomless. There is widely rumored to be a city of Chaos below, kept at bay by the water and the endless rain.
I often imagine it as being kind of comparable to Lake Tahoe, although Tahoe is about twice the size of Skyfall Lake. Still Tahoe is a good reference for ideas:
In winter, all that rain coming down results in vast snow falls throughout the eastern Far Place and the Stinking Forest.
The Stinking Forest is a rainforest? Parts of it receive heavy snowfall. But it is not a temperate rainforest (although the Vale of Flowers might receive enough moisture to qualify).
Think of it as something like a lake effect.