Thankyou for the responses. Your right, its probably better to focus on autumn sightseeing.
Is it possible to do daytrips to ski resorts from somewhere like Tokyo, Nikko or Osaka, Kyoto, Hiroshima etc? The only thing I wonder is whether toward the end of our trip (if it does snow early) or there are some reports of snow around we could always make a couple of daytrips to a nearby slope? Or would that be too hard/ not feasible.
If it's an option I might book our last few days somewhere nearby (within a few hours train ride) of a resort which is known for a long season on the off chance