Yes, Finnish summer is unpredictable. Yesterday it was a sunny day with almost +30 degrees, now a heavy rain and +13. One more option for a typical Finnish summer day is broken skies with a strong cold wind :) .
One day it's rainy and cold, the next day it's sunny and warm, like today: 28°C. Refreshing rain is just a distant memory. But that's the charm of Finnish summer. You never know what you'll get!