We have an expression in Austria about the weather in April:

Austrian> April, April, der macht was er will!
English translation > April, April, he makes what he wants!

As some mentioned before, April is very unpredictable. It can be sunny,
and some moments later you have heavy snowfall. Typical weather in April.
Best months to tour middle and southern Europe are May and June.
Normally it's conveniently warm, and rainfall may be rare. Many years ago, we suffered on very high temperatures in May, this year we had a few days with 35°C!!