Rain the Dolomites

I spent a week in that area in July 2015. I think there was rain on two days. I happened to be down in the valley on both occasions and don't know what was going on up in the mountains.

In my experience, mountain weather is always unpredictable and cool weather, often accompanied by rain, is a substantial risk even in mid-summer. What you're seeing in the forecasts doesn't have anything to do with this year's specific weather patterns. You need to be a lot closer to your travels dates to have anything approaching a decent prediction. Even then, precipitation projections just don't seem very reliable.

Bolzano has the museum housing the Iceman. It is an excellent, modern museum and enjoyable by children as well as adults. The city has a really beautiful, colorful historic district. There are other museums as well, but the ones I remember are art-related and perhaps not of so much interest to the kids.

Bressanone is smaller and has another pretty historic district. But no Iceman.

There is rather frequent bus service running through the major valleys. You can always hop on a bus and stay dry while you enjoy the scenery.

Depending on where you're staying, Verona might be a viable day-trip. I haven't been there myself and can't offer any specific suggestions.

The rain forecast reflects the fact that late afternoon, evening, or nighttime thunderstorms are common, much like in the Rocky Mountains. (Denver gets a storm nearly daily at some times of the year.) We have seldom had a complete rainout in the Val Gardena and we’ve spent about 8 weeks there in the past 6 years. Get out early (like 8:00) and take advantage of the clear mornings. If it is raining in the morning (rare in August) the afternoon will probably be better. As mentioned above, Bolzano for the day is a good plan, too.

Weather in mountain areas is unpredictable and may change in few minutes. Bringing a light rain jacket is always advised, but in the in case of exceptionally good weather. A common weather pattern is that days may start sunny, but humidity builds up and it gets cloudier during the day, with a possible small shower in late afternoon. This is strictly a local pattern - for example rain is less likely in Dobbiaco (wide valley) than in Moena (narrow valley). But of course a pattern of really good or really bad weather over a larger area will override local patterns. Long and demanding hikes cannot really be planned in advance but you must wait for the best day in a row. Some hikes in rainy weather are not fun at all, they could even get dangerous. This is why it is not too wise to plan short stays in mountain areas, as you are betting against the weather.

Consider that my parents began bringing me to Dolomites when I was three; after I grew up and began going on my own, I preferred the Austrian Tirol that is near and very much like Dolomites. So I have more than fifty years experience of holidays in the area, averaging 10 to 20 days in August. I have experienced all possible weather conditions, from two weeks of uninterrupted shining sun to disastrous floods. Most years are mixed - 3 sunny days, 3 rainy days and so on; the really good ones are rare, the really bad ones are more frequent at present times but still not the majority. - By the way, the most devastating flood happened when I was three, on my first holiday. After half a century, I can still remember it :-)