Weather in southern Germany

You could look up the historical averages in May and September for the places exactly where you are going

For example https://www.accuweather.com/en/ch/appenzell/311917/month/311917?monyr=5/01/2018#

Some things to know:

• Weather is unpredictable in Germany until 3-4 days in advance. Do not trust other statements.
• DWD is the official weather service, also responsible for regional warnings.
• Weather can be very local in alpine region - one side of mountain rain, other side sun.
• Temperatures will always depend on the altitude - rule of thumb: -0.5C per 100 metres.
• A month is a long time. Example September: On 9/1 it is meteo summer, on 9/30 it is autumn.
• Tip: Look into climate tables from planned destinations, e.g. on Wikipedia, to get the range what it can be.
• Tip: In Appenzell visit Säntis mountain.

Thank you. This is good information.

If you're in southern Bavaria (Oberbayern) in mid-May, chances are it will be warm to hot. I have been in Munich enough times in May where daytime you'll be quite comfortable without wearing a light jacket, warm to hot, likewise in Berlin. Don't rely on the charts, I never go by them.

Obviously you have to look at weather sites and averages but...we were in Germany September 6-22 2013 and it rained all day every day except for 2 days. We still had a good time, but it got really depressing at times.

That's what I meant with very local weather, in this case regional. If you compare the amount of rain in the states of Germany you will see that in 2018 Bavaria had nearly double amount of rain compared to Berlin (statictic in German language).

May is better than September. It may rain, but it's getting warmer, with little humidity.

Thanks, everyone, for the input. Very helpful. I guess there are a lot of issues that would seem to be more important when traveling overseas, but for whatever reason, weather is way up at the top of my list. :-)