I want to go hiking in the European Alps during the summer (preferred hiking elevation 1000-3000 m). I don't mind the location but I want to have the highest chance of sunny weather. What are the places with most sunshine in the Alps? Are there some official meteorologic data for this?
I couldn't find a resource that gives detail for all the countries, but I was able to find information for the different countries:
Here's a table with the average values for the power per month for different places. Not all of them are in the Alps though.
There's also an interactive map for the sunshine hours, however that one doesn't have the averages over many years, so you'd have to pick out one particular year, obviously not as good as the other one.
On a personal note I could recommend areas in Valais, Switzerland. Especially the Southern valleys e.g. around Zermatt and Saas-Fee don't get a lot of rain.
Here's a map for the sunshine hours for every month.
Here's a map for France also for sunshine hours, unfortunately only the average over the year, so probably not very useful.
Here's a report on sunshine duration in Italy, there's monthly graphs for different places.
CAUTION: Please note the maps below show solar power (kWh/m2), which exactly is not what I was looking for, because it depends on geographic location (latitude) - the more to the south you go, the more energy you get from the sun for the same amount of sunshine. Hence, values only in a relatively small area can be compared.
During my search I found some maps for the photovoltaic industry that show the Alpine region:
Both these are by Photovoltaic Geographical Information System (PVGIS) where you can also find more detailed maps (usually by country) if you want.
Also, if you live in Europe and want to compare your home location do a desired destination in the Alps, you can use one of these maps that show whole Europe:
From what I see in the maps probably the best location regardless elevation is French Alps and southwestern Italy or one has to climb high enough above the clouds pretty much anywhere.
Other answers focus on the total power of sunshine on a yearly or monthly basis. Since you're in for outside activities and not for generating electricity from the Sun, I think that as a tourist, the total number of hours of sunshine on a monthly basis more relevant. For Switzerland, Meteoswiss records such figures. The map below is for the entire year:
The tables have the distinct advantage that they record information per month. The sunniest location certainly depends on the season, so if you find a year-based map you may end up quite disappointed!
Other national institutes may record similar data, but there is no unified data source, so you would have to check it per country.
What Relaxed said; no way can you guarantee in advance. I spent last June through September in Switzerland, whose north had a lousy summer, especially July. But the Graubunden lived up to its reputation as being sunnier than elsewhere, and I enjoyed some very good weather after I had abandoned the incessant drizzle of the Oberland for Zermatt. OTOH when I returned from Zermatt to the Oberland, I found new snow (in August!) at the same altitude where I had previously enjoyed flowering meadows.
In the Alps you can really improve your weather by a shortish train ride. My advice would be to stay south of the Rhine-Rhone watershed, or be prepared to move there sharpish.