Do we need A/C in Lauterbrunnen and Lucerne ?

Lauterbrunnen should be fine without air conditioning. You may not even find places with it.

Lucerne can be in the mid- eighties during the day that time of year. The issue with European hotels is that the windows do not have screens, so if you sleep with the windows open, bugs can come in. But my experience has been it will get cool enough at night to sleep with the windows closed. Google average temp for August. Perhaps others can chime in.
Safe travels.

Lucerne can be a bit noisy (at baby's bedtime, not concerned about later), so that would be my concern more than temperature or bugs. So, it may depend on location.
Last October was the warmest on record, I wore short sleeves in both places. No telling!

I was in Lucerne this past June and it was stuffy in my room at the hotel des alpes even with the small fan provided by the hotel.

I would aim for air conditioning in Luzern.

We are booked into the Continental Park (recommended by Rick Steves in his 2020 guidebook) because it has A/C rooms! We are there just after you. This hotel is also close to the train station. https://www.continental.ch/en/

The last time we were in Luzern we had a rental car. I was hesitant to trust the vehicle to a valet or to pay self-park it in a large garage for fear of damage. We stayed in Meggen at the Hotel Balm: https://www.balm.ch/en/hotel/rooms/ with free parking and a bus stop right in front of the hotel which, with the city pass, meant a free 15-minute ride to the city. Our room had a view across the lake to Mt. Pilatus. The included breakfast was amazing. We had dinner at the Bistro and enjoyed it so much that we hope to return if we can when in Luzern in September.

This castle hotel in Luzern has A/C in the rooms, but probably gets some cooling breezes as well. Rooms start at CHF 350/night with breakfast for your dates. Nice safe parking is 15 CHF extra per day. And it should be nice and quiet at night for the baby’s nap time.

https://www.chateau-guetsch.ch/en/

My husband and I hiked up to the chateau when we were in Luzern for one night last August. We saw it from the town and were intrigued. We did not go inside, but we did explore the grounds. And then he hiked around in the forest nearby before walking back to our hotel and changing into swimwear for a swim in the lake.

Given that the standard room is only about 40 CHF more than we paid at Hotel Ameron Flora, we might give it a try if we return to Luzern.

A top-floor hotel room at Hotel Stern was a bit hot for me back in early July 2018, but it was an extreme case: just under the sloped roof, with a roof window that could not let much air in.

By late August, the days are much shorter and evenings are therefore cooler: given how scarce A/C options can be in Lucerne, I would take my chances... But if you do find an A/C room that suits you regarding budget, location and amenities, go for it!

Who owns the Chateau Guestch? There is a free funicular that would be fun to take and then have a cocktail at the American Bar.

The funicular was not operating when we walked up there at the end of August, but it may be back in operation now.
You can read about the history and some of the illustrious guests, from Queen Victoria to Henry Kissinger to Shirley Bassey, here:

https://www.chateau-guetsch.ch/en/our-history/

Who owns it? According to the homepage (scroll down to the bottom), the host is Andreas Gartmann. But a woman we began talking to while admiring some classic cars on display below the chateau said the current owner is Russian ( and she was not happy about that.

If you can read German, this article is from the local newspaper Luzerner Zeitung:

https://www.luzernerzeitung.ch/zentralschweiz/luzern/chateau-guetsch-in-luzern-kirill-androsov-ist-der-neue-besitzer-ld.2149253?reduced=true

I am putting this in a separate post in case it is deemed inappropriate and removed. This satire about Fasnacht in Luzern may reflect the attitude of the locals toward the current ownership of this historic hotel.

https://www.luzernerzeitung.ch/zentralschweiz/kanton-luzern/fasnachtssatire-sensation-das-guetsch-ist-jetzt-eine-schlossklinik-fuer-den-alternden-mann-ld.2415915?reduced=true

I usually travel in the spring or fall shoulder seasons, and have been very comfortable in Lauterbrunnen without A/C. I often spend a few days in Lucerne as well, and the hotel I normally use doesn't have A/C. The room often gets a bit stuffy and uncomfortable in the late afternoon and evening, but the hotel was able to provide a fan and that helped. At that time of year, I would definitely suggest A/C in Lucerne.

It depends on how you tolerate a little warmth. My wife does not tolerate anything over 70 degrees. You might be uncomfortable if you are like her, make sure that you have a fan just in case.

My family stayed in Lauterbrunnen last week, and it was pretty hot, getting up to 87 degrees with high humidity. It felt more like Jamaica than Switzerland, and only dropped to the high 60's at night. We curtailed our hiking plans and only found relief in 7,000 ft or higher altitudes (e.g. Kleine Scheidegg, Jungfraujoch, Männlichen, etc.) where it was in the 60's. I've been to this area twice before in summer, and have never seen it so uncomfortable. I think they're going to start to need AC if this kind of weather becomes more frequent.

Thanks for the current weather report. We are going to be in Lauterbrunnen in late August- hope it has cooled down some by then - at least to sleep. Here in FL we live and work in A/C at all times during summer months, so I can't tolerate the heat/humidity. There were very few places with A/C in BO area.

It has indeed been hot here lately, but normally at night the temperatures drop sufficiently so you can cool down. You should keep windows closed during daytime, and open them at night. (I have mosquito screens at several windows, so I can generate a nice cross draft at night). Because houses are sufficiently insulated that usually keeps it cool indoors.

If such hot days become more common we will have to adapt. I hope it will not entail more AC. Trying to solve everything by just throwing large amounts of energy at it is exactly why we are having climate change...

WengenK, your suggestions are good for apartments and homes, but the problem is that a lot of hotel rooms do not have the possibility for guests to set up cross breezes, install insect screens, etc. And to be honest, quite a few of the nice older hotels are not modern buildings that keep heat out. Some of the hottest, most uncomfortable nights I have spent in Switzerland were at hotels, including in Wengen. I do think more hotels should probably invest in screens for their windows so people can keep them open at night without bugs, and put fans in all rooms without people having to ask for them.

As for the summers, many hotels still use the old excuse that "it's only bad a few nights a year" - unfortunately this is no longer true, especially in lower elevation places. The 7 warmest years since records began in 1864 have all come since 2010 and it's pretty clear that this trend will continue. I don't think AC will be installed everywhere due to expense and environmental issues (and even where it is installed here, there are often rules about how low the temperature can be set which do not match most Americans' expectations). Generally it does cool down pretty well in the mountains, so wouldn't worry as much there, especially in the earlier and later part of the summer - the cities are a different story and "heat islands" are becoming a big issue here, especially in older buildings.

I would say for mid-June through August, if you are very sensitive to heat, you will want A/C in the cities. Just be aware that the a/c offered here (and elsewhere in Europe) may not be as cold as what you are used to the in the US. In the mountains, it is harder to find hotels with A/C and it is less of a must-have. If you're worried about heat, perhaps better to rent an apartment where you can at least have multiple windows to air things out in the evening as WengenK suggested. In this case, the original poster should be fine in Lauterbrunnen.

Just a tip I learned accidently. As stated above, keep all window and shades closed during the day. Once the sun sets, open all the windows you can and prop open up your hotel room door. This will draw out all warm air from your room and bring in the outside cool air. Almost every hotel has drafts throughout hallways and staircases. Do this for about 10 minutes or so and then shut the room door. It will level off the heat build up in your room. It works almost 100% of the time if you do not have AC.

Great advice here!! I’m taking notes.

I’m questioning my decision to stay at the hotel des alpes again next June as I was pretty warm last June. I keep checking the hotel des balances to see if their prices come down.

RS still is recommending the Continental Park in Lucerne in his 2023 Switzerland book. Will be able to evaluate it when we stay there in September. But based on the help we've received thus far in terms of their concierge assistance in trying to get us tickets to the KKL free concert and helping us find a good fondue restaurant I'm impressed!

"We don’t have any screens in our home and open everything up in the night, there really aren’t that many bugs to worry about."

Wengen unfortunately has lots of bugs. Its a humid place, and you'll notice the bogs when you walk in the area around it. I've been fitting screens to quite a few windows. Its an advantage that windows open inwards here.

Most hotels in Lucerne do not have A/C, and the few that have it tend to be expensive. We stayed there in June several years ago in a hotel that did not have A/C and it was uncomfortably warm. Maybe in late August your chances are better. This year we were there and stayed in the Radisson Blu which has A/C, but it was very expensive.

I stayed in Lauterbrunnen last week, it was pretty hot (mid-80s) (and other surrounding areas where it got into the 90s....all with no A/C) and like others said, just make sure blinds/curtains are drawn during the day. Once the sun went down, we opened our balcony doors or windows and left wide open at night. Most hotels provided a medium size fan, and we also each had a small personal fan. It was fine, and I'm normally a very hot sleeper (I keep my AC on 62 at night at home!)
I never once in 2+ weeks had trouble sleeping b/c of the heat. Part of it may be that we were so tired each night, we would have slept through anything!!