How’s the weather?!

I think your question is best answered by reviewing the most recent five years' worth of actual, day-by-day, historical weather statistics on the website timeanddate.com. That should give you a good idea of the range of conditions you may run into. I don't know that we have anyone on the forum who regularly travels to the Bernese Oberland in early October.

Be aware that temperature varies greatly at different altitudes. Wengen isn't as high as Murren, so if you make a side-trip to Wengen it will probably be warmer there.

We spent a week in Murren in October 2017 prior to boarding a river cruise in Basel. We did a RS tour to Switzerland in 2016 and were familiar with the area. The first week in October worked out great for us. We saw a dusting of snow the first day but it cleared up after that and we enjoyed 5 days of sunny, cool weather. We had brunch on the Schilthorn, did a day trip to the Jungfrau, and hiked around Gimmelwald and Trummelbach Falls. No crowds. 👍

I was in Switzerland the first week of October 2017. For the Bernese Oberland part of the trip, a friend and I stayed at Gimmelwald, just down the mountain from Mürren. We had some rain, and intermittently wore a jacket/fleece, but it was pretty comfortable. Warmer clothing was worn for trips to mountain peaks.

Will all the fall colors still be in their glory!?

Mürren is at a high elevation. I remember a lot of evergreens, not so many deciduous trees. Colors were good, as I recall, on the train ride from Lausanne to the Berner Oberland.

Dave is right about the trees - very few deciduous trees above the valley floor, a few visible from Gimmelwald but I have no idea of what any colour would be left...

@disneygal48. From my travel diary.

Sept 29th, 2018, Sat. Drove from Montevarchi, Tuscany to Lauterbrunnen, arriving around 2 pm. We elected to drive via the mountain pass roads. Both for the scenery and to experience roads we had not taken before. The temperature on arrival was around 18c, a glorious day. Walked the main street to get bearings. Had purchased meats, cheeses, beer, and other drinks at a co-op in Interlaken and in the evening, sat eating on the balcony of our rented house overlooking the town of Lauterbrunnen with the waterfalls cascading a little further up the valley.

Sept 30th, 2018, Sun. Cable car up to Grutschalp then train to Murren. A leisurely day, with the children approaching the cows with trepidation and then being a little taken back by the sound of the cow bells. Around 17c and a little wispy breeze. A slow lunch al fresco on the deck of the Edelweiss Hotel soaking up the view of the mountains across the valley. Close to a perfect day.
Plans had been made to cable car to the Schilthorn for a snap with a young and handsome uncle George. My wife put paid to those plans by managing to crack 4 ribs when in Montevarchi.

Oct 1st, 2018, Mon. Weather changed overnight. Cloudy, drizzle and barely 6c. Drove up the valley to look around and went to the Trummelbach Falls. Took a train ride to Kleine Scheidegg. Had snowed overnight and settled with a between 2 and 5 centimetre build up.
Interlaken for evening meal. Had been recommended the Husi Bierhaus. Tried a couple of their craft beers and schnitzel of course. Children were eager for chips as they had not been allowed them in Italy. Meet a fellow countryman at the bar. That day he had been to the Jungfraujoch. In his words “mate, it is brass monkey weather up there”.

Next morning left for north eastern France.

You asked about autumnal colours. Checked my videos of the area for the time. Concur with Dave and Nigel’s comments. Green pine trees and other green indigenous trees and bushes. The odd yellowing of leaves. Definitely not reds, yellows and browns like in your new England region.

Neither Interlaken nor Lauterbrunnen were crowded, rather best described as comfortable. For me, an enjoyable time of year in this part of the planet.

Hope this helps a little.

Regards
Ron

We were in Murren and Bern 2019 mid October and the weather had some really nice, sunny days - highs around 50's and then foggy, light snow weather.

In early October 2015, my husband and I spent one night in Zermatt, Switzerland and one night in Monstein, Switzerland to board the Glacier Express the next day. Zermatt was warm that day (@75 F.) When the clouds lifted, there it was--the Matterhorn in all its glory. That evening we did not require even a sweater. That's hardly scientific, however, I won't forget the next night in Monstein after dinner in a small mountain-
grouping of 3-5 buildings (I couldn't call it a village), we took a walk to listen to the cowbells in the dark. It was crisp and we could see our breath. I'd say @ 30 F. We weren't there for fall colors but for the breathtaking mountain views. There was snow on the mountain tops. The next day we spent in Zurich and overnight where it was warm. The elevations in Switzerland are wildly varied as is the weather. This link speaks to fall colors and has some lovely photos. https://www.brit.co/switerland-fall-travel-guide/