Local Chamonix Weather Tip and Info channels
When the foehn effect is present, it's unsafe to fly. The foehn is usually associated with strong southern winds at altitude (southwest to east, sometimes north east). Watch out for the arrival of a storm front with high pressure on the Italian side of the Mont Blanc range and low pressure on the French side. Foehn conditions cause strong gusts of turbulence.
You can access local weather balloon information (in French) on the French Flying Federation's (FFVL) radio frequency, 143.9875, or by telephone, 04 56 38 6080 (costs 0.15 Euros per minute) or by internet on the following sites: Charamillon and Brévent.