Meteo Takayama in agosto

Hakuba-forum threads on August weather across Japan describe the mountains as a genuine relief from the brutal heat and humidity of Tokyo or Osaka, valley temperatures noticeably milder thanks to elevation even at the height of summer. Posters are direct this doesn't mean settled though, afternoon thunderstorms building fast in the Japan Alps and posing a real hazard on exposed ridgelines, lightning strikes genuinely not rare here. Regulars recommend an early start for any serious hike to be off exposed terrain before storms typically build later in the day. Obon week, usually falling mid-August, is flagged as the peak domestic travel crunch, hotel prices spiking and availability tightening around that stretch. The Happo-one Fire Festival and other local summer matsuri are worthwhile additions to an August visit beyond the hiking itself. The record: 28.5C days feeling like a punishing 33C, 20.9C nights, an extraordinarily high 254mm across nearly 24 days and 88 percent humidity.

Takayama's forum is consistent that November is the transition month, not full winter: by mid-month a cold wind picks up and light snow can fall, but it's the kind that melts rather than piles up on the streets, since Takayama sits in a basin rather than up in the mountains. Real snow season, posters agreed, doesn't properly start until December. Expect cold mornings warming a little by afternoon, and layer up - one traveler compared the feel to a chilly October day in the northeastern US, more brisk than bitter.

May is good weather in Takayama — 20°C by day, 10 overnight, before June's heat and rain — but it falls between the two things the town is best known for. The Sannō Festival, the spring half of the Takayama Matsuri and one of the three most beautiful festivals in Japan, runs 14–15 April; the autumn festival is in October. May gets you the old town, the float exhibition hall and the Japanese Alps without either crowd. The record does show rain on fourteen days, so "before it gets wet in June" is a relative claim.