What temperatures should we expect in mid-May?

May- Average high 73 degrees F., Average Low 42 Degrees F.

70 to high 80s

Normally in the 70s but this is a seasonal question - you should check the weather conditions always when you actually plan to visit. No one can predict rain and of course construction. Right now there's is construction happening till at least mid 2018 in the south entrance (springdale).

I would suggest to check weather report as there will be so much variation in weather conditions. When we visited it was below freezing temperature but still pleasant. You may want to avoid visiting when its raining.