I know this title sounds crazy but I don’t know how to phrase my question better
In: 5716
I did a bit of resewrch into this for a school project that we were hosting outside in December, but it’s not a super in depth explanation.
“Feels like”, otherwise known as “wind chill” on windy days, is a reference to *how quickly* an object or your body loses heat. What the weatherpeople are specifically trying to say is “It’s X degrees outside, but you’re losing heat as if it was Y degrees.”
For example, let’s say it’s 32°F outside, and it takes 30 minutes for a bowl of water to freeze solid when left outside in the shade with no wind. Now let’s say the wind picks up, and the water now freezes in 15 minutes instead of 30. The wind chill, or what the air *feels like*, is lower than the actual temperature of 32°.
Bodies and physics are wonderful and weird. I will answer from the perspective of someone who is interested in making people feel comfortable in buildings (I can’t speak to the biological side).
Heat is just energy. Energy moves around in different ways. Energy is also measured with different tools, depending on the form it takes.
One way is radiation. When you stand next a hot oven with the door open, you are feeling radiation heat from the oven. If you stand next to a cold window, and one side of you feels cold its because you are radiating away to the window. The cold surface sucks away your energy.
Another way is conduction. You’ve probably heard of this in electricity and maybe heat too. Every material will “carry” heat from one place to other. materials that do this badly are called insulators. Air is a very good insulator which is why most of the “insulation” in our buildings actually work by trapping air.
When you put your hand on a warm surface, you are conducting heat away from whatever you are touching. When you put your hand on a cold surface (like a cold steering wheel), the surface is conducting heat away from you.
Then there is convection. When a gas or liquid gets warm, it expands: it gets lighter than cold gas. The warm gas or liquid starts to float. Heat doesn’t rise, but hot air does, which is one reason why it is often warmer near the ceiling than near the ground.
The last bit is about humidity. It takes energy (heat) for phase changes – think melting ice or water drying away. Did you ever do that experiment where you measure the temperature of a pot of water while its boiling? It stays at a consistent 100C (not sure what that is in F) until all the water boils away – the water stays consistent but the steam temperature increases.
So when we wet a surface and let it dry, the water uses the energy from the surface to transform into vapour (drying off). If the water is on our hand, we feel our skin loosing energy in the form of feeling cooler.
If the air is moving, the speed water evaporates is quicker, so we feel colder (more energy is lost more quickly). If the air is already pretty moist, the water doesn’t evaporate and we don’t feel cooler. Funny example of this, I rode a motorcycle in the rain with gloves that weren’t waterproof. My hands weren’t cold while it was raining. Water couldn’t evaporate from my gloves. As soon as the rain stopped, my hands went numb really quickly because the air was drying out my gloves so fast.
Most thermometers measure heat through conduction; air molecules touching the sensor. Thermographic cameras measure radiation and estimate temperature based on radiation and the type of material being photographed (its a wild set of equations). We can measure air humidity and air velocity directly and estimate how the temperature will be perceived by humans.
When we design buildings for comfort, we have to take into account the temperature of surfaces (e.g. the cold window or floor), the speed at which the air is moving, the humidity of the air, as well as the direct temperature of the air. Mechanical engineers and architects can play with all of these variables to make a comfortable space. Or do it badly and make hell in a box.
Generally they’re measuring by two different techniques. First is dry bulb. That’s what the temperature is, with no regard to other factors.
The second is wet bulb. This takes into account humidity and wind chill.
Both of these are important because in high temperatures, a high humidity doesn’t allow sweat to work as well. So it will feel hotter than it is.
Conversely on the other end, if there’s wind, it will blow away any warmth on the surface of your skin, making sure you feel every bit of the cold.
Since it’s ELI5 and not ELI15 I’ll try to make it very simple.
The temperature in the air is the same, but it can feel colder if it’s wet or windy outside.
Guys, I don’t think OP is asking why wind and humidity make us colder. They want to know how people are able to put a number on ‘feels like’, since a thermometer can’t feel the effects of wind chill like a human.
Best explanation is this, imagine standing outside in 95f summer heat without any breeze. But once you are in your car and driving 35mph with windows down. All of the sudden it doesn’t feel like 95f but much cooler.
Wind will cool you off in any temperatures but a thermometer doesn’t need any cooling nor heating thus can record actual temperature.
What you « feel » is not heat, but heat transfer. The faster the heat transfer, the « hotter » something feels, up until it starts damaging your skin where it isnt registering as heat but rather pain.
A thermometer cannot measure heat transfer rate, because it is essentially the same temperature as its environment.
> We calculate a ‘feels like’ temperature by taking into account the expected air temperature, relative humidity and the strength of the wind at around 5 feet off the ground (the typical height of a human face!), combined with our understanding of how heat is lost from the human body during cold and windy days.
https://blog.metoffice.gov.uk/2012/02/15/what-is-feels-like-temperature/
The ”fels like” is calculated based on the comparison between a dry bulb thermometer (normal thermometer) and a wet bulb thermometer. (A thermometer with a wet wick over the bulb) it also takes into account the wind chill factor which affects how fast something cools off.
Like you’re five, if it is -10° with a “feels like” of -17° the coldest any object will get is -10°. But the speed at which it cools from normal to -10° is the same as if you put it in a -17° freezer
I preferred the “wind chill.” It became the “feels like temp” a few years ago.
How’s a meteorologist gonna tell me what weather’s gonna feel like? MF doesn’t even know what I’m wearing.
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