How should I dress for Germany in July?

Average temperatures are not very helpful, as they do not accurately reflect the variations. In my recent experience with Germany ( Berlin, Munich, and the Bavarian Alps around Garmisch-Partenkirchen) you can expect anything from hot and humid to cool and rainy--- that is what we have experienced in July and August. Most likely is warm and pleasant, but be prepared for the extremes as well.

We too have experienced the extreme summer weather conditions described by Lola from the summer that never happened to heatwaves.

Check a 10 day forecast a couple of days before you leave to get a more accurate idea of what the weather will be like during your trip.

Wear what is comfortable and is a good style for you. If you are going to be in cities a lot you may want to pack a cute skirt or summer dress. If you're going to be villages and hiking for a few days you may need shorts or summer pants and nice t-shirts. Comfortable shoes are a must. Check the 10 day forecast and your locations and pack accordingly.

I think the same summer clothes that you would wear in the US will work fine for Germany. I noticed that people seemed to dress more for comfort than for fashion and that made me feel just like I was at home in the Pacific Northwest! Good shoes, a light jacket in case of rain, and the ability to layer if necessary are helpful.

I did notice that only American teenagers wore the very short shorts and they tended to stand out.

In the summer, cool weather is usually associated with rain, so a windbreaker with good water resistance would be a good idea.

The other responders got it exactly right, so I won't repeat their excellent advice.

Thanks for all the great insights, everyone! You've all been very helpful!