Places in Europe will not all have the same weather forecast as the ones in the other continents. The Northern Europe's spring season may be a bit wet and cooler than the spring in Italy or Spain. And there is less rain in England, Scotland and Ireland this season as compared to the other European countries.
Summer will be a lot hot and humid to some parts like in Italy and Spain. However, summer in Germany, Switzerland, Norway, Sweden and Denmark may be a lot cooler than the ones in Greece, Portugal, Italy and Spain. So, avoid going there on summer if you can since most travelers coming from all parts of the globe and even the Europeans take their summer vacation and flock to the seaside areas in Europe. This can drive up the accommodation and transportation rates high.
Schedule your travels to Europe on spring where it is not yet that crowded and the weather is still manageable. I have traveled during the autumn season as well (late August - mid October) in Europe and the weather was a bit cold already, dipping to a low of 5-10 degrees Celcius at night. But noon time temperature was acceptable. The accommodations are cheaper because of lesser occupancy rate and the tourist spots are not that crowded.