TMB Weather Overview
The Tour du Mont Blanc traverses altitudes from 800m (valley floors) to 2,600m (high passes). Weather changes rapidly and can vary dramatically between valleys. A sunny morning in Chamonix can become a thunderstorm on Col de la Seigne by afternoon.
Month-by-Month Breakdown
June (Mid to Late)
- Temperature: 5-20°C (valley to pass)
- Conditions: Snow patches likely on cols above 2,400m. Wildflowers at peak bloom. Some refuges still closed early in the month.
- Crowds: Low to moderate
- Verdict: Beautiful but unpredictable. Bring gaiters and check trail conditions daily.
July
- Temperature: 10-25°C
- Conditions: Best overall weather. Long days (sunrise 5:45, sunset 21:15). Occasional afternoon thunderstorms.
- Crowds: High — this is peak season
- Verdict: The safest bet for weather. Book everything months in advance.
August
- Temperature: 10-25°C
- Conditions: Similar to July but with more afternoon thunderstorms. Haze can reduce visibility on hot days.
- Crowds: Highest of the season, especially first two weeks
- Verdict: Reliable but busy. The second half of August sees crowds thin slightly.
September
- Temperature: 5-18°C
- Conditions: Cooling temperatures, shorter days, autumn colours beginning. Snow possible on high passes after mid-September. Some refuges close after the 10th.
- Crowds: Low — the quiet season
- Verdict: Our favourite month. Fewer people, beautiful light, crisp air. But have a backup plan for early closures.
Weather Patterns to Know
Afternoon Thunderstorms
From July to early September, convective thunderstorms build most afternoons, especially on the Italian side. Plan to be over high passes by early afternoon. Start hiking by 7-8am.
The Föhn Effect
Warm, dry winds from the south can create unusually clear conditions on the French side while the Italian side is clouded over. Check forecasts for both sides of the massif.
Temperature Inversions
Valley fog with clear skies above is common in September. If you're sleeping in a valley and see fog, the passes above will likely be sunny and warm.
Best Weather Resources
- Météo France: Most reliable for the French stages
- MeteoSwiss: Excellent for Swiss stages, with mountain-specific forecasts
- Météo Chamonix: Local forecasts tailored to the Mont Blanc area
What to Pack for Any Month
Regardless of when you go, always carry:
- Waterproof jacket and trousers
- Warm layer (fleece or puffy)
- Sun protection (hat, sunscreen, sunglasses)
- Gloves and beanie for early morning passes
See our complete packing list for detailed recommendations.
Ready to Plan Your TMB?
Use our interactive planner to build your custom itinerary, find refuges, and download GPX files.
Start Planning