How much rain in Scandinavia in July/August?

I hope you know that Scandinavia is a vast region with very different micro climates. The western regions of Norway sees a lot of rain, whereas eastern Norway and Sweden beyond the Norwegian mountains sees a lot less rain. Altitude will also make a huge difference.
Since you ask about Copenhagen, the summer months typically sees more heavy showers, thunderstorms and torrential rain (and more recently due to climate change). On those days rain can be very heavy for short periods of time, with high winds as well. However you can also have days with near constant drizzle. It's the weather, there is no guarantees.

Thanks for the reply. To be more specific, I am following the Rick itinerary, primarily hitting the bigger stops: Copenhagen, Stockholm, Helsinki, Tallinn, Oslo, Norway in a Nutshell, Bergen. I definitely read that Bergen and that side of Norway was wetter, but from what I have found in books and on weather websites, it seemed like the rest of Scandinavia seemed similar for summer rainfall (except Stockholm being a bit drier). Temperature seemed to vary more, but not rainfall. That's why I don't totally trust the generalizations of the guidebooks and websites and am looking for any additional insight. Thanks to all.

Just get one of those light weight water resistant with a hood windbreaker and skip the umbrella

A waterproof/water-resistant jacket protects against both wind and rain. An umbrella is more of a liability in high wind conditions. Dressing in layers is as applicable to summer as winter, with summer requring less (lighter) of an insulation layer than winter.

Here's one data point. We were in Copenhagen, Stockholm, Oslo, Bergen and the fjord country last July for over 3 weeks. We had rain 1 day - an afternoon thunderstorm in Copenhagen, as Morten mentions above. The rest of the time was either cloudy, partly cloudy or sunny. Our 3 days in Bergen were sunny & clear. We had waterproof rainshells and really needed them once. The rest of the time they were "windbreakers" and even that was a minimal need since that month was extremely nice. However as they say: Past Performance Does Not Guarantee Future Results. I would not count on our experience as the norm, it was likely the nice tail of the bell shaped curve.

Hi, koryjay, me, too! Except instead of your Sweden etc after Oslo- Bergen via NIN I am going up the coast of Norway north to Kirkenes and then Inari, Lapland before Helsinki and Copenhagen. Packing has been a real challenge, especially trying to stay under Norwegian Airlines 22 lb limit for bag and personal item. I am taking a dark blue weatherproof anorak with a big hood and visor ( Outdoor Voices), since I almost never use an umbrella in the US🙄living in the NW; it just adds weight, whereas the jacket can be for cooler days even if it doesn't rain. I have a superlight merino long sleeve top that could go under a tee or on its own under the anorak. I decided to buy a sweater once in Norway, instead of bringing one! "Two birds with one stone." I have also been watching the long range weather forecasts. Lastly, shoes- I have some waterproof hiking " sneakers" I will use on days when it does, or could, rain...have a wonderful trip!