Problem is that you can't change ground tiles dynamically. You can script to change placeables, like snowdrifts and herbs and trees, but you can't change a tile, or add and remove water within a script.... or at least any way that I know of.
You'd have to have two versions of an area, a "spring" and a "winter" version, which would mean physically changing them in the mod every 6 game months or so. A big PIA for the developers.