We are considering a week long stay in Murren this August 22-29, and we are wondering what the weather is like in late summer. We have visited Murren several times in June and July, and it was usually lovely (but sometimes there was rain, even light snow in mid June, and a couple of thunderstorms in July).
That's a pretty safe time to visit. August in Switzerland-German-Austria can sometimes get uncomfortably hot, but a high altitude location like Mürren offers relief to a certain degree. Conversely, it could get rather cool in the mountains, but generally not uncomfortably cold.
Precipitation is not predictable, unless you consider montly averages, which aren't terribly relevant for short stays.
We were there August 28 to Sept 1 last year and enjoyed good weather. Definitely needed sweaters and a light jacket, even light gloves a couple of times. It poured one evening, but otherwise we were out in cloudy to partly cloudy weather each day. The last night, it snowed overnight and we awoke to new snowfall on the mountains, not accumulating in the town, but walked to the station in a light snowfall on our way out of town.
Going back in late Sept this year but staying in the valley for ease of transportation. Hoping for moderate weather!