April in Europe is known for noticeably warmer temperatures than the prior season. That said, this all depends on where you're staying (and what you'd regard as 'warm'). If you're staying in year-round sunspots like the South of France or some coastal regions of Spain, you could see temperatures mirror summertime. On the flip side, a mountain resort in Austria will still be chilly - you may even still be able to plan snowsports there in April!  Thermal camping gear is a must and will offer protection against all weathers.