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Humidity and perceived temperature

aggle-rithm

Ardent Formulist
aggle-rithm
Joined
Jun 9, 2005
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Location
Austin, TX
OK, I just got back from Colorado, and so in the last six months I've been there both in wintertime and summertime.

In the winter, it seems about ten degrees warmer than it does in Texas at the same temperature because the air is so dry.

In summer, it seems about ten degrees cooler than in Texas, also because the air is so dry.

How can low humidity make it seem both warmer and cooler at different times of the year?
 
Well, when it's humid your sweat doesn't evaporate as well so you won't cool off as quickly as you would in dry air. No idea how that would make you feel warmer in the winter though.
 
excaza said:
Well, when it's humid your sweat doesn't evaporate as well so you won't cool off as quickly as you would in dry air. No idea how that would make you feel warmer in the winter though.
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I didn't even realize there was an effect in cold weather until last winter when I went to Steamboat Springs. Everyone was looking at us funny because we were wearing heavy coats in 30-degree weather.

(Also, you can't make snowballs in low humidity. They just crumble.)
 
Now the cold I am aware of, a damp cold feels worse than a dry cold for sure. But I am not up on the science of it.

In terms of how uncomfotable 'hot' feels I think I prefer the dewpoint temperature anything above 65o dewpoint feels 'muggy', anything in the 70s feels 'tropical'.
 
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excaza said:
Well, when it's humid your sweat doesn't evaporate as well so you won't cool off as quickly as you would in dry air. No idea how that would make you feel warmer in the winter though.
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Perhaps the humidity is not the variable. Elevation is. While it is colder at higher elevations overall, the Sun is also going through less atmosphere. It feels warmer at a colder temperature when you are in direct sunlight in CO than it does at a warmer temperature here in WA when the clouds block direct sunlight.
 
Skeptic Ginger said:
Perhaps the humidity is not the variable. Elevation is. While it is colder at higher elevations overall, the Sun is also going through less atmosphere. It feels warmer at a colder temperature when you are in direct sunlight in CO than it does at a warmer temperature here in WA when the clouds block direct sunlight.
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But then, wouldn't the temperature be higher?
 
aggle-rithm said:
But then, wouldn't the temperature be higher?
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No, the atmosphere is thinner so the ambient temperature will be lower.

Then depending on the amount of snow on the great, the reflected sunlight can make it appear warmer than it is
 
Water holds heat better than air. Moist air is also more dense than dry air at the same temperature.

The moisture is the more significant factor, though. In hot weather moist air essentially blocks our body's cooling mechanism--persperation simply sits on the surface of our skin, rather than evaporating and cooling us. When a system's primary cooling mechanism shuts down, it heats up; doesn't matter if the system is a computer, a car, or a human. As for cold, moisture from the air contacts our skin, and (because moisture has a higher heat capacity) sucks out our heat--basically the same thing as persperation, just at a time when we REALLY don't want it. And considering most of the "winter" clothing we have in the USA at least does nothing for blocking moisture, it really doesn't matter how warm you bundle yourself up, you freeze.

This is demonstrably not an altitude thing, either--I've experienced heat and cold at similar elevations but drastically different humidities, and the effects are exactly what the OP describes. I used to work in Alabama and Georgia, which are very humid environments. Summers are unbearably hot, and winters can be bitterly cold, even at 30 degrees F (to put this in perspective, I've done geology field work at -20 F in Ohio--anything positive temperature shouldn't feel cold to me). In the summer you just suffer, but in the winter I'd put my rain jacket on over my coat, and after my coworkers realized I wasn't nearly as cold as they were they stopped laughing and followed suite. Contrast this with the Mojave desert, which isn't much different elevation-wise (well, the bajads of Antelope Valley aren't, at least). The summers are hot but not unbearably so (can't speak to the winter, as I wasn't in the field much, but my experiences in Ohio, at similar elevations, deal with that). It's definitely the humidity that's the major factor here.
 
Moisture in the air can't absorb heat very well. Water vapour has a slightly higher heat capacity than dry air, about double, but there just isn't very much of it: ~0.4% by weight at 0C, dropping to ~0.2% by weight at -10C. If the humidity matters, it matters in the same way: evaporation from your skin cools you down. You can be cooled by ~5C even during the winter.

If dry air seems warmer then something else is to blame. Personally I'd guess wind speed, but without knowing where you were in Colorado and Texas I can't confirm anything.

Dinwar, if a rain jacket made you warmer, then the blame is really on your coat. You don't need a winter jacket to be completely impermeable, but if water can easily get through your coat then so can air. A coat isn't doing anything if it's not trapping the air around you.
 
aggle-rithm said:
But then, wouldn't the temperature be higher?
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No, the surfaces in direct sunlight heat up but the air doesn't. I think because it is thinner it conducts heat more poorly.


Whoops, I see this was answered. Nice to see we concur.
 
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Dinwar said:
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This is demonstrably not an altitude thing, either--I've experienced heat and cold at similar elevations but drastically different humidities, and the effects are exactly what the OP describes. I used to work in Alabama and Georgia, which are very humid environments. Summers are unbearably hot, and winters can be bitterly cold, even at 30 degrees F (to put this in perspective, I've done geology field work at -20 F in Ohio--anything positive temperature shouldn't feel cold to me). In the summer you just suffer, but in the winter I'd put my rain jacket on over my coat, and after my coworkers realized I wasn't nearly as cold as they were they stopped laughing and followed suite. Contrast this with the Mojave desert, which isn't much different elevation-wise (well, the bajads of Antelope Valley aren't, at least). The summers are hot but not unbearably so (can't speak to the winter, as I wasn't in the field much, but my experiences in Ohio, at similar elevations, deal with that). It's definitely the humidity that's the major factor here.
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No argument on the humid heat thing, and about the humid cold thing. But you are wrong that the altitude has no contribution.
 
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Skeptic Ginger said:
No argument on the humid heat thing, and about the humid cold thing. But you are wrong that the altitude has no contribution.
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While ambient temperature is affected by altitude, the feel of that temperature is not -- which is, what is being communicated here.

The same ambient temperature, with different humidities, will feel different.
The same ambient temperature, at different altitudes, will not feel different.
 
Water vapor is actually lighter than air. So bathroom fans are in the ceiling to exhaust the humidity, to prevent mold and also lower the humidity. It's kind of counter intuitive, I always though they were there to exhaust the effluent from using the toilet.

So what was the question? Oh yeah, comfort. Humidity makes you feel more extreme because humid air , in the cold, absorbs more heat. But in the warm, it prevents sweat from evaporating.So sweating is less effective, and it is a positive feed back system- the less heat absorbed, the more you sweat, which makes the air near you skin more humid, which allows less evaporation....
 
aggle-rithm said:
OK, I just got back from Colorado, and so in the last six months I've been there both in wintertime and summertime.

In the winter, it seems about ten degrees warmer than it does in Texas at the same temperature because the air is so dry.

In summer, it seems about ten degrees cooler than in Texas, also because the air is so dry.

How can low humidity make it seem both warmer and cooler at different times of the year?
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I had to read this a few times because of the way it's worded; it still seems backwards. At least according to the humididex. Warm air should feel warmer as the humidity goes up. If I read your post right you're saying the opposite.

What's wrong with you? :p

As people have pointed out I think you're experiencing the effects of altitude and not humidity, or at least more so.


ETA: you'll notice from the wiki article Windsor ON, has the record for humididex. As a life long resident I claim expertise in humidity. Last week the humididex had to be close to 50, it felt like wearing wet wool sweater to the beach.
 
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3bodyproblem said:
As people have pointed out I think you're experiencing the effects of altitude and not humidity, or at least more so.
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I'm not so sure. As a former spelunker I can say that in caves it is usually 100% humidity; one's breath is often seen while speaking. But it is not cold, even with light clothing, even given that where I caved the temperatures were about 50 degrees F. The clothing used, if worn outside at that temperature and much lower humidity, would have been too light to stay warm. Now, I admit that caving is somewhat strenuous and 50 degrees isn't all that cold, but I never really felt cold in a cave like I sometimes did being outside at similar temperatures.
 
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