Born in December in MI, spent most of my first 48 years there, worked outdoors for about 30 years.
-10°F is doable wit the right clothes. I always hated the heat and could stay comfortable at 20 forever. Have experienced both hypothermia and heat exhaustion. After my heat sickness I had zero desire to ever be hot again. First full year here in FL had 130+ days over 90°. Some places I've worked here were more like 130°.
Our avg or normal body temperature is 98.6, so 90 is below that. However if working, you are burning calories (read btu's) and creating heat. Staying hydrated is crucial. It was 90-95 last weekend and when I took the woman out for a ride we wore our leathers. It was not hot and we both were comfortable.
What's the wind chill when 110° at 80mph?