Here is a list of the ski areas which are open after 5/8 (Mon) (*() shows the last operation date).
Now, only 6 ski areas are open in Japan.
Gassan (6/11), Kagura (5/21), Shiga Kogen (*Shibu-toge, Mt. Yokote) (5/31 5/14), Tateyama (Lower June),
Mt. Norikura (Lower August), Senjoujiki (Lower May)