In reply to davkeo:
Autumn can be a golden, settled period. The first half of September is often - though not always - superb for rock routes, with few of the afternoon storms you can get in hotter months. Do bear in mind the days are much shorter, though, and the nights chilly. The good weather of early September can last all month, and well into October.
However, fresh snow will not quickly melt, so a single snowy day can wreck rock conditions for the rest of the year, other than on south faces. As for ice and mixed: as already stated, it mainly depends on the summer. Autumn can be an amazing time with routes such the Cecchinel - Nomine and the Dufour on the GPA in incredible nick. Or it can be totally hopeless.