If you have done the My Way Alpine (or G/A/S) tour in JULY or AUGUST....

Did GAS back in July 2016, and I've also been to Chamonix prior to that in July.

For Chamonix, it was sunny for our time there. I wouldn't say it was hot, but we had clear skies during our two nights. In fact, soon as we got there we bolted to the Aguille du Midi to take advantage of it. However, it being the mountains, anything can happen.

For GAS... Salzburg was warm and clear. By the time we got to Vienna it was hot and humid. We stayed in Murren, not Lauterbrunnen, and unfortunately it was cloudy most of the time. That was the bummer for me. There were ocassional periods of sun but ultimately we rarely got the mountain views. I think the only time was when we hiked down to Gimmelwald and got a halfway decent view. Down in Lauterbrunnen, it varied between rainy and cloudy.

Sad as that was, by the time we got to Hallstatt it was clear and warm, and we took full advantage of our time on the lake. So that made up for it a little.

I was on this tour last August. Salzburg - The weather was very nice and quite warm. We stayed in Bolzano - when we arrived the weather was warm and very pleasant. The next day for hiking, it was cool and cloudy. By the time we took the gondolas up to the meadow for hiking, the weather became cold and cloudy, it started raining shortly after we started hiking. It gradually began raining so hard, most of us turned back. I personally got soaked to the skin. My jacket was “water resistant” which wasn’t good enough. The people who had gortex stayed nice and dry.
Füssen - was cool and showery, but I stayed fairly dry. We were going to up the Zugspitze, but the mountain was so fogged in that we just had lunch and didn’t go up. From Lauterbrunnen on through to the end of the trip, we had lovely weather. Even though we were in the mountains, I never really felt cold. If you decide to go to the Jungfrau, you’ll probably want a warmer jacket or at least plan on layers.
Enjoy your trip, I love it!

We took a GAS tour in late August.

Salzburg (mid-trip) was warm. Munich (at the end of the trip) was warm. Halstatt and Murren were chilly and misty. The Schilthorn had snow!

So, basically, you need lots of light layers, to be ready for anything.