It's a work in progress but the developer of Winter Overhaul is off to a good start.
This mod adds snow to the Commonwealth. And it's smart about it. For instance, if you're walking through a dense forest, there will be a ton of snow. Wide open areas like marshes won't have as much.
The developer has also released a companion mod that adds snow to the game's roads, sidewalks, and some bridges.
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We expect this mod to improve over time so keep an eye out for frequent updates.