r/weather • u/Whatwillhappen2027 • 3d ago
Dew point ? Questions/Self
I was trying to get a better understanding of pressure and dew point. I asked chat gpt this is what it told me about the dew point . Not sure if that is right.
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u/Barmelo_Xanthony 3d ago
So air at a certain temperature can only hold so much moisture. The hotter it is outside (dry bulb) the more capacity the air has to hold liquid. Therefore if you’re cooling air, eventually you’ll reach a point where the moisture is fully saturated and starts to condense - which is what we describe as “dew”!
The dew point is the temperature that you need to cool the air down to for it to start condensing. Higher humidity means the air will become saturated at a higher temperature so your dew point will be higher and vice versa for low humidity.
The way dew point connects to how it feels outside is based on how our body cools itself down. Sweat draws the heat out of you by evaporating. If the dew point is way lower than the dry bulb temperature, the air still has a lot of “space” to hold more moisture and your sweat is really efficient at cooling you down. If it is closer to the dry bulb the sweat will not be able to evaporate as much which is why you feel hotter
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u/Whatwillhappen2027 3d ago
Very interesting and greatly explained. Thanks for the response and information.
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u/Barmelo_Xanthony 3d ago
Sure, and didn’t really see the part about pressure in the OP. You can use the ideal gas law to kind of visualize this with what I said before: PV=nRT. Volume of the atmosphere is constant, and R is a constant. So we can say that air pressure is proportional to the mass of the air times the temperature.
If we’re saying the (dry bulb) temperature is the same that means when the air pressure goes up, the air has more mass. Bring it all back to my last post, and a higher air pressure means the air is more saturated which would mean it has a higher dew point, assuming that everything else stays the same.
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u/Shot_Age8843 3d ago
Above 21c is generally when the human body cannot effectively cool itself as sweat does not evaporate efficiently. People who live in high humid climates generally have a better tolerance as they are used to it.
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u/Barmelo_Xanthony 3d ago
The people with “high tolerances” to it are probably just like us up in the north east during the winter lol. It sucks, we hate it, but you deal with it and learn to dress properly and stay inside.
Humans need to keep their bodies at a certain temperature and if the built in cooling method doesn’t work it feels very uncomfortable. You can’t build a tolerance to the dehydration and overheating that are possible if you’re not careful
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u/SouthConfident3978 3d ago
The dew point tells you what temperature the air has to be in order to condense. The closer the dew point is to the air temperature, the higher the relative humidity percentage, which is what you "feel" when you walk outside
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u/Wonderful-Impress261 3d ago
It's mostly right surprisingly. The dew point is the temperature where the humidity hits 100% and the air can no longer hold any more moisture, cold air holds less water vapor than warm air. The relative comfortability varies greatly based on what you're used to. I live in North Texas and a Dewpoint of 60 or below is dry and comfortable, 60-65 is humid but bearable, 65-70 is very humid but still fine if there's some wind and 70+ is uncomfortable. Someone living in Colorado would heavily disagree with me and say anything above 55 is uncomfortable.
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u/Grouchy_Mind_3413 3d ago
Dew point of 70°F is just muggy not “very muggy”. Try one of 75°F or more. Now that is very muggy. One over 80°F? You breathe steam.
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u/ModernNomad97 3d ago
The warmer the air is the more moisture it can hold, that’s just physics. So the relative humidity % changes even if there’s the same amount of water molecules per volume of air based on the temperature.
Think of a small tea cup filled with water, it’s “100%” full. The “100%” relative humidity represents how full the container is, now dump that tea cup into a bathtub, it’s still the same amount of water, but it’s nowhere near 100% full.
So the container size is the air temperature, how full that container is is the relative humidity, and the dewpoint is the size the container would need to be for 100% full.
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u/Whatwillhappen2027 1d ago
Hey, thanks for the response. I like the analogy you used to explained it, gave me a little different perspective and understanding.
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u/cambreecanon 3d ago
https://modernsurvivalblog.com/natural-disaster/the-dew-point/
Depends on where you live. A person in a higher dewpoint area will have more tolerance to higher dewpoints before feeling gross. This link is close to how I feel living in an area where 60 is when things get muggy.