I'd say 40-90 degrees if you plan to do Jungfraujoch and the lakes around Interlaken. 50-80 if you're staying up in the mountains and not doing those 2 extremes.
It gets REALLY hot down in Interlaken so you'll want shorts and tank top for down there. For up at the Jungfraujoch I wore a sweatshirt and pants and was completely fine, but I guess we all have different preferences when it comes to cold. I grew up in the midwest so my cold tolerance is fairly high.
I personally would never pack a winter coat of any kind for July/August in that area but a sweatshirt, light jacket/rain jacket and a hat are definitely a good idea. For most days in the mid level ranges around Murren and Zermatt I wear yoga pants and a t-shirt and then have a sweatshirt in my backpack. The high altitude sun can make it feel warmer than it actually is and in Murren I'm out sunbathing on my balcony in July/August every day. On the cloudy days it's still rarely even close to chilly except in the evening.