Its 33°F right now but it feels so cold that I really thought it was like 10° out. But a week ago I remember being outside and it felt pretty nice. I checked and the temperature was 36°F. It should feel the same shouldn’t it?
I also notice this happens when the season changes. When summer is ending and the temp starts to drop into the 60s it feels so cold but when winter is ending and it starts to go *up* into the 50s and 60s it practically feels like summer.
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You can’t actually feel how hot something is. All you can feel is how hot it makes you.
This is why when you go down a plastic slide on the playground on a hot summer day the slide feels warm but the metal rivets feel super hot. They’re actually the same temperature, but the rivets can transmit that heat to you much better.
Heat can be transferred to you in a few ways. One is just by touching something hot, which is known as conduction. That’s what’s going on in the slide example. Different material properties can make this go faster or slower.
Another form of heat transfer is when something carrying heat moves around, typically a gas or liquid. On its own this doesn’t transfer heat to you, but moving air can quickly cycle out the layer of air next to your skin. On a cold day your skin warms up that layer (making your skin colder), then if the wind blows it away that layer is replaced by a fresh, cold layer for your skin to warm. This is why wind chill exists–at the same temperature you’ll tend to feel cooler when there’s wind.
A third form of heat transfer is when one body sends heat in the form of infrared radiation. This is how a toaster toasts bread and how the sun toasts you. If you’re being cooled by the air as you’re being warmed by the sun it’ll result in a warmer overall feel than if the sun was behind clouds or if it was just night.
Complicating all of this is evaporative cooling. When water evaporates it cools down. This is how sweat works to cool you. The rate at which you sweat (or are otherwise made wet) and the rate at which that sweat evaporates determines the magnitude of that effect. Still humid days will do little to allow sweat to evaporate, so the heat index will be high on those days. Dry windy days will quickly evaporate sweat and help to cool you off.
From there you’d look at biology. What feels pleasant is largely driven by the thermal balance of your body. You generate a good bit of heat just through your life processes, or some extra heat when exercising. Your body needs to get rid of that heat. However, your body also needs to stay warm so the various chemical reactions that make up life can proceed as desired, which means not shedding too much heat. An ideal heat flow balance will depend on how much heat your body is producing, so a person exercising at 65 F may find the temperature to be unpleasantly warm, while a person idle at 70F may find it to be cooler than they’d like.
And finally you can look at psychology. Biology can tell us what heat balance is “right,” but how unpleasant should other heat balances be? Someone who is used to the cold may not be bothered so much by a cold day, even though that weather is requiring them to burn some extra calories to stay warm.
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