Meteo Matsumoto 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.

Regulars are specific this can swing wildly by the end of the month, one day mild and pleasant and the next genuinely freezing, a medium-weight coat with sweaters layered underneath the standard advice regardless of which day a trip lands on. Our row backs that cold, genuinely wet read, 13C over 0.4C nights feeling as low as -3C, with a substantial 146.6mm of rain across 13.5 days and real snow, 43.8cm, still falling at this elevation in the Nagano highlands. Regulars are consistent conditions run noticeably colder here than in Tokyo or Osaka at the same time of year, hiking in the surrounding mountains needing a genuinely clear-day forecast check rather than just general trip dates. Layers built for a real range remain essential throughout. The record: humidity 71 percent, 8.6 hours of sun and an 11.2 kph wind.

Regulars are careful to separate three different odds that get conflated: the chance of a typhoon somewhere in Japan this month is genuinely high, the chance one makes landfall is lower, and the chance it hits your specific location at your specific time is very low - with a typhoon's aftermath often bringing perfectly clear weather rather than lingering disruption. Our row backs a wet, still-warm month, 27.3C reading as a hot 30C, over 17.6C nights, with a real 215.2mm of rain across 17.6 days. Regulars specifically recommend October over this month for those wanting to avoid both the heat and the higher typhoon odds, though most days here remain clear regardless. The record: humidity 82 percent, 8.2 hours of sun, an 8.4 kph wind and one of the cleanest air readings in this project, AQI 34.

October is the month for the mountains behind this town, and the reason is a closing date rather than a peak. Kamikochi is at its best in October for the leaves, but after the first week of November it turns cold, it can snow, and most places up there shut for the season - so a trip built around the valley has to be inside October, not adjacent to it. The town itself is mild at 20.4C, though the nights drop to 9.6C, a gap of eleven degrees to dress for in a single day. Rain is the part the board does not raise and our row does: 205.1mm across 16.4 days, with sunshine down to 7.3 hours. The record: humidity 80 percent, an 8.8 kph wind and AQI 33.

June is tsuyu here and our row shows it: 206.7mm across 16.5 precipitation days, about twelve millimetres a wet day, under 9.2 hours of sun. What regulars add is the shape of it. The rainy season is a stationary front rather than a blanket, so it does not rain everywhere in Japan at once and several consecutive wet days are possible without the whole trip being lost; the storms tend to get heavier towards the end of the season. The casualty is the view - Matsumoto Castle's top floor looks out at the Northern Alps, and cloud takes that away before it takes anything else. Inland at altitude, the days stay comfortable: 27.4C falling to 16C at night, with almost no wind. The record: humidity 77 percent, 14.6 hours of daylight and AQI 51.