August is generally hot across Europe these days...it's unpredictable of course, but in general, you'll have better luck the further north you go. I've spent a few summers in Norway and, although you will have some warm days, it's generally nicer with a mixture of blue-bird cottony cloud days, rainy days, cold and windy days, and a few warm ones here and there. We usually go up along the central coast in the Alesund area. Very pleasant! Scotland is also a good choice...up in the highlands and along the coast it stays generally cooler.