Went through dated photos of all the April trips we enjoyed over the last decade; summer dresses to jackets to long sleeves to swimming costumes with sun capes to raincoats to cardigans to sun dresses. If you plan for each day to be a bit warmer than you expect it to be whilst also finishing up considerably cooler than anticipated you’ll be fine.
Whilst the month can be very variable, I have found the marked dip in temperature at the beginning and end of each day to be very consistent. Be sure not to get caught out.
And watch out for allergies if you are prone to them.