Hi,
Never been that early, May is the earliest we've been (twice).
Temp according to AccuWeather for April 2016 was at a low of 21 degrees - 27 degrees at a high through the day. Evenings were a bit nippy at 16 degrees on average.
I would guess you'd have a bit of rain at times and if it's like September you may also have some fantastic thunderstorms!
Some places would be open, but many will just be getting sorted for the start of the season really.
Hope this helps
