I will be in Chamonix in September for 3 days. I hope to hike? What if it is raining (hard)?
You might have to change your plans - maybe go somewhere else since everything will be obscured by clouds anyway.
John, I'm sure that there is not much hiking going on if it rains hard anywhere. That being said, my wife and I were there in early October and the weather couldn't have been better. Clear blue skies. Paragliders everywhere. No jackets needed at 11,000' on Aiguille du Midi. Just perfect. But, you take your chances.
Do a day trip to Martigny in Switzerland.
Head over to Aosta, Italy through the St. Bernard tunnel...or go over the St. Bernard pass and visit the St. Bernard museum and the beautiful dogs. We were just there today and it was amazing!
There is the St Bernard Museum in Martigny-might be good for a rainy day. The train ride through alps in that area has some gorgeous scenery.