I think that's it - it hasn't been starting out cool in the morning, so once it starts to heat up it heats up a lot faster, and takes forever to cool down. Maybe the cloud cover is holding in the heat at night. Late afternoon hunts are always hot this time of year, but at least mornings are okay. But lately even early mornings are already very warm/hot.
I must say though later in the season mid-day it's great weather. Here on Fort Gordon (because a tiny bit of the post is in Jefferson County and considered the southern zone) we get that extra two weeks or month or whatever. Granted the whole state might get that now since rule changes, I don't know. But 50 or 60 degrees in late December or so is awesome!