Greetings all! I'm sure I could get averages off of the internet and likely any suggestions made here are just gonna be best guesses, but I figured I'd check in with you guys that visit frequently to get thoughts on traveling with outerwear in CH during May. We will be arriving 8 May and staying through 19 May. We'll be all over starting in Lauterbrunnen for several days, then on to Lucerne, and finishing in Zurich. We will be visiting Jungfraujoch, Schilthorn, and probably doing at least one more mountain excursion from Lucerne. Other than that we'll be roaming around the LB valley and the various towns dotting the mountain side there, possibly a day trip to Lugano, but otherwise roaming around the cities.
I've been to CH twice before, albeit a decade ago, and both times were in Nov / Dec. Never been in the "summer" season. Jungfraujoch was quite chilly then and I know with it's altitude (and the fact it has a year round winter sports area) that it never gets warm there, but I have long since traveled the Rick Steves way with a carry-on backpack and packing as light as possible.
Just want to know if a lightweight down jacket like you would get from UNIQLO would be sufficient for the time we'd be spending on the mountain tops without it being too cold to really enjoy things. We want to do some of the activities at the top like the zip-line or snowboarding, but I also don't want to carry along a really heavy coat for all of the trip if it's not necessary.
I appreciate your thoughts and any direction you can provide!