Switzerland - September or October?

Nobody really knows next year weather, but on average September should be much better than October. The summer weather pattern is going to break sometimes in September or October, the later you go, the greater the risk of bad weather.
There was a time when I was spending ten days every August in a little Swiss side valley near St. Gotthard massif. Some years were better, some were more rainy. I remember going back once for a day on a September 21h, and in that year it was already snowing on top of mountains.

The shift in the weather usually happens by mid to late October. The earlier part of the month is usually the best time of the year for hiking. You have the least chance of rain (but that doesn't guarantee none), and you'll avoid the very rare heat waves that can occasionally creep into September.

Snow can fall at any time of year in the Alps... I've seen it in every single month of the calendar. But during warm months, it quickly melts and falls as rain at lower elevations.

We were there in late Sept/early Oct last year, 4 nights in Zermatt and 7 in Lauterbrunnen. We brought layers, but it was so cold up on the mountains in Zermatt we ended up buying base layers for under our hiking pants yet one day ate lunch outside in shirtsleeves. By the time we got to Lauterbrunnen it was better: wicking tee-shirts and light jackets sufficed. We had no rain until departure day, which was extraordinary. Late Sept through October is our favorite time to travel in Europe. We've had terrific luck with weather and (lack of) crowds.

KC,

I've usually travel in the Berner Oberland in September and have been there as late as about mid-October. In my experience the weather is usually good at that time of year, but of course no guarantees as it can vary from year-to-year. During October I found that even though it can be very comfortable during the day when the sun is out, it cools off considerably in the evenings so taking some clothing for layering is prudent. It's also a good idea to be equipped for rain at any time of the year.

Thanks for all the input. It sounds like "dressing in layers" is the theme for Switzerland. I'm just hoping that should there be poor weather it doesn't spoil the view.

You definitely need layers and should be prepared for almost-winter conditions. We were there in late Oct/Early Nov and luckily didn't have much rain but it was sunny and dry and cold. And up top on the Schilthorn the wind was a-blowing, which made the paragliders happy. Plan on a sweater every day and an outer layer like a packable down jacket or raincoat some of the time. Also think about waterproof shoes since soggy feet are never any fun, and packable umbrellas.