Temperature by altitude
Summit temperature and wind chill from the valley forecast, with what to wear.
0℃
Higher means colder
Air thins and cools as it rises, so temperature drops about 0.6°C for every 100 m of elevation. On a 25°C day in the valley, a summit 2,000 m higher is 13°C. The top of Mt. Fuji (3,776 m) sits at 2–3°C when sea level is 25°C, and that is in August.
Summit temperature ≈ valley temperature − (elevation gain ÷ 100) × 0.6
Wind makes it worse
A useful rule of thumb is about 1°C of perceived cooling per metre per second of wind. On a ridge at 10 m/s, 13°C feels like 3°C. Add wet clothing from rain or sweat, and evaporation pulls heat out fast enough to cause hypothermia in summer. This is how people "freeze" on Japanese mountains in July.
Dress in layers you can change
Climbing is hot; ridges and breaks are cold. One thick jacket cannot cover both, so wear thin layers and adjust often.
| Layer | Job | Example |
|---|---|---|
| Base | Move sweat off the skin | Synthetic or wool long sleeve. Not cotton: it stays wet |
| Mid | Insulate | Fleece, light down |
| Shell | Block wind and rain | Rain jacket, wind shell |
A rain jacket is also your best windbreaker, so carry it on clear days too.
The temperature in a city forecast is for the valley. For Japanese mountains use a mountain-specific forecast such as Tenki to Kurasu (てんきとくらす), Yamaten, or Windy, which give temperature and wind by elevation.
Recommended gear
ミズノ｜ベルグテック EX ストームセイバー VI
¥14,900 Rakuten price (2026-11-02)★ 4.62 (144)
耐水圧 30,000 mm・透湿 16,000 g の上下セットがこの価格。ゴアテックス製の半額以下で、性能は日帰り〜小屋泊には十分。「最初のレインウェア」として最も多く推奨されている一着。
Best for: 最初の 1 着。予算 1.5 万円以内で上下揃えたい人
耐水圧 30,000 mm 透湿性 16,000 g/m²/24h 重さ 約 580 g（上下・M） 収納 付属スタッフバッグ
Prices are 2026 guides.