In an average year, Nagano's autumn leaves reach peak color around November 12. For an October 11–20 trip, the chance of overlapping peak color is ~0%, and the chance of seeing at least some autumn color is ~5%.
Across October 11–20 in an average year, expect roughly 10 days of still green. Leaves still mostly green — colour hasn't reached this city yet in most years.
Some links on this page earn us a commission from qualifying bookings, at no extra cost to you. About.