I got to spend a short week in the Mont Blanc range during the last week in September. My partner Erwin and I stayed up at the Cosmiques hut not far from the upper station of the Midi gondola. We did some ice and mixed routes on Mont Blanc du Tacul/Triangle du Tacul to spend as much time climbing s possible. Our finishing tour was the popular Cosmiques ridge route back to the Midi gondola station.
We stayed up high because that's where the conditions were at their best. It was clear that the region had gone through a particularly hot and dry July and August. A lot of lower mixed lines and north faces were ice and snow free, or in very bad shape, and therefore prone to rock fall.
Our timing was good: we arrived at the end of a brief storm and the start of a stable high pressure system that lasted for the week. Temps were cool ( the 0 degree line was between 3000 and 3200 meters) with no real wind.