It has been difficult for me to find a comprehensive list of ski resorts in Japan, in English, with functioning links.
Well, for Tohoku at least. I have finished a massive project, organizing all of my snowboarding research into 6 spreadsheets (SPREADSHEETS ARE SO INTERESTING) that you can sort with links to all the active websites I could find (websites which, unfortunately, are mostly in Japanese).
If you have solid Japanese skills or the patience to use your web browser’s translate function you can use Snoway.com, my most frequented source for information but Snoway is still incomplete. Also, before you hop in a car or on a train, I would verify directly with the ski resort that they are actually still in business. Post 2011, many of these places have had trouble getting skis and boards on the mountain and tourism in general is depressed all around Tohoku, particularly in Miyagi and Fukushima.
These lists are not complete. Many of the ski resorts in Japan are small municipal parks with or family owned. My research method consisted of cross referencing wikipedia.jp, snoway.com, snowjapan.com, skijapan.com and area searches on google maps. It is likely that I missed a small resort or two. If you know of any that aren’t on the list that are cool and worth checking out please send them along or leave the info in the comments. More over, I have included ski trail map links to the larger places.
All that being said, this is likely the most comprehensive list you will find in English.
There you go. I hope you get out on the mountain and shred some serious pow!
If you want to the whole list in in excel format: Tohoku Snow Project