Body temperature is generally hotter when days are longer and colder when days are shorter.

“There's also an important way in which temperature matches day length in general as days get longer, it tends to be hotter out. Not always, but in general, that's the way it is. And as days get shorter, it tends to be colder outside. So temperature and day length are also linked metabolically. They're linked biologically they're linked, excuse me, and atmospherically they're linked for the reason that we talked about before about duration of day length and other climate features and so forth.”