We'll be doing an Elbe River cruise between Prague and Berlin in early July. What kind of weather, especially temperature, should we expect in either city?

In my experience, warm and humid.

Who can tell? very variable. Just Google average weather for any spot and any month.

it's summer, it's not going to be totally unpredictable what it's going to be like, just go to holidayweather.com and find averages.

It didn't strike me as excessively humid that I noticed (but then I live in a humid place, it's wasn't noticeably humid to me), but when I was there in summer, it was really hot one year when there was a big European heat wave, and just kind of normal another year. I think typically around 80F in afternoon, not 90-100, at least usually. I think Berlin is a little cooler on average than Prague.

https://www.accuweather.com/en/de/be...weather/178087

Prague Average Weather in July - Holiday Weather

sites like these also give predictions for weeks in advance - of course predicting weather is not all that great the longer out.

Ave highs in either city for July avg about 74 F - perfect with about 8 days of rain.

Probably no need of AC

If it doesn't start raining soon you'll be moving around in a coach. Expect warm weather, usually not too high humidity, occasional showers.

Ingo - do most folks in Dresden/Prague/Berlin climes have AC -would OP want to request AC?

No, Pal - hardly someone has A/C in their private homes.

There can be an obvious differences between not having and needing A/C in one's private house or apartment and wanting A/C when staying in a hotel.

Unless you live in a tiny apartment, you usually have enough windows in your home for sufficient ventilation to keep it cool or moderately warm inside. But when you stay in a small hotel room with just one window, it's not really much of a relief when it's hot outside during the day.

It's also so much of a gamble whether it's a hot or cool summer that most people rather suffer a few days during a heatwave than waste several thousand of euros on A/C, which may only be really needed for 1-20 days in one whole year.
But as a visitor you probably don't care that much about spending or "wasting" 10 or 20 euros more a night on a hotel with A/C to make sure that you can sleep at decent temperatures if there will be a heatwave.

Do you wonder why so many hotels in Germany HAVE A/C when it is "not needed?" The average humidity in Berlin and June is 60%.