I made a snowy map a long time ago. It sucked horrible balls(There are no words to describe how horrible it was. z-fighting, falling through map, not very fun at all.), but here is what I learned:
Use a grainy texture(such as sand) with the white turned up if you are going to go full snow. Just be careful about the lighting. If you make it too bright, then it will make things hard to see. You may counteract this with heavy fog and a snow storm.
If you go full snow, make sure it fits the environment.
If there is full snow, make sure there are plenty of objects breaking it up. Full snow can be very bright.(unless there is a snow storm, then only place objects to draw attention or if necessary.
Also, so I don't regret missing this opportunity: "NEVER go full snow."
You can if you want, I was just quoting that one movie...