42, my friends, is blowin' in the wind

OK, so there's no wind at the moment, but the early-morning low is indeed 42°F as the Sun rises.

Starting to feel decidedly autumnal out there.  Time to switch the HVAC from "cool" to "heat", at least at night.  (And why, oh why, do residential thermostats have a mode switch instead of "heat if below" and "cool if above" settings?)