Every station in Japan that measures snowfall, not just the places that already have lifts. Pick the seasons you care about and it averages new snow over exactly those, so you can see which towns get buried and which merely have a reputation.
Faint grey marks every weather station in the country — enough of them, scattered widely enough, to trace the shape of Japan without a basemap. Coloured points are the ones that measure snow, shaded by how much they averaged over the seasons you choose. Click one. Pinch or ⌘/ctrl-scroll to zoom, drag to pan, double-click to go deeper — station names appear once you are in far enough to read them.
Worth being blunt about what this can and cannot tell you, if the question is where to build.