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  #1  
Old 30 July 2012, 05:17 PM
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Canada "Wet cold" vs. "dry cold"

Comment: I have a question about what I think is a myth but is comonly
believed.

There is a common misconception that "wet cold" vs "dry cold" result in a
different experience ie: a very cold place that is "dry" feels less cold
than a place that has high humidity." Therefore a place like Toronto that
is 25 degrees fahrenheit but more humid feels colder than Calgary at 10
degrees fahrenheit but is drier.

I have read (somewhere) that this is a myth - that below freezing the
levels of humidity in the air have no effect whatsoever on perceived
temperature to people. Of course, the reverse is true in warm
temperatures: high humidity in the air makes it feel much warmer
("humidex".)

Virtually EVERYONE in Canada believes in the "it's cold but it's a dry
cold so it isn't so bad". I have heard the explanation for this perception
is that dry cold tends to occur in sunny places so people feel better out
in the sun vs a wet cold where it is overcast.
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  #2  
Old 30 July 2012, 05:34 PM
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A wet cold glues your whiskers together, icing your mustache till you look like a walrus.

A dry cold just freezes your nostrils shut.

Both kinds of colds are enough to freeze the brass balls off a canon ball bearing witch's monkey.

Is that the correct expression?

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  #3  
Old 30 July 2012, 05:39 PM
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At least around here wet cold is something that happens closer to freezing and once it drops below a certain temperature it is always dry cold.

That said, when we have very damp weather right around freezing I fnd it hard to feel warm even if I am in the house.
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  #4  
Old 30 July 2012, 05:43 PM
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It probably isn't below freezing on most "wet cold" days here, but it certainly feels a lot colder and less pleasant than "dry cold" days, while skiing for example, which are below freezing. You don't need to read it in books - it's about perception; you can feel it for yourself just by experiencing both...

I'm sure there's a point where even dry cold becomes unbearable - I found it in Seoul for one - but that's not really relevant. After a point, around 0 degrees C I assume, the water freezes out of the air anyway and so it's all "dry cold".

(eta)
Quote:
I have read (somewhere) that this is a myth - that below freezing the levels of humidity in the air have no effect whatsoever on perceived temperature to people.

... I have heard the explanation for this perception is that dry cold tends to occur in sunny places so people feel better out in the sun vs a wet cold where it is overcast.
That doesn't make sense anyway. It doesn't really feel colder, it just feels as though it feels colder? Hmm...
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  #5  
Old 30 July 2012, 05:47 PM
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I know that early spring rain days feel colder than snowy days in winter to me. I always thought it was psychological, because in spring the temperature goes up and down, whereas in winter is stays down constantly.
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  #6  
Old 30 July 2012, 05:47 PM
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It always seems warmer to me if there's snow on the ground (to reflect the light, I assume)--how would this fit in?
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  #7  
Old 30 July 2012, 05:48 PM
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Quote:
Originally Posted by Richard W View Post
I'm sure there's a point where even dry cold becomes unbearable - I found it in Seoul for one - but that's not really relevant. After a point, around 0 degrees C I assume, the water freezes out of the air anyway and so it's all "dry cold".
Around -40 Celsius, it no longer matters if it's dry cold or wet cold...


But if you sweat or your clothes get wet because you're in deep, wet snow, then it matters, because you'll get hypothermic much faster.
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  #8  
Old 30 July 2012, 06:06 PM
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Heavt breathing

To the extent that the air holds additional moisture, it will be much more able to take heat away from your body. All substances have a property called 'specific heat' which is the ability of that substance to absorb and release heat energy. The water molecule has one of the highest specific heat ratings, much higher than any other significant gas, due to its angular shape. As air gets colder, its ability to hold water as vapor decreases, until you get to where precipitation happens - the dew point. When air with a substantial amount of vapor blows across your skin, it absorbs heat more readily than very dry air. As noted above, very dry air is always dry - it just cannot hold much moisture.

Quote:
Originally Posted by Avril View Post
It always seems warmer to me if there's snow on the ground (to reflect the light, I assume)--how would this fit in?
That may be. Another factor is that the snow can get much colder than freezing temp readily, so it may be 'absorbing the cold' (technically, it would be rleasing its heat to the air right above it, making a layer near it which is not as cold as higher up), depending of course on the wind.
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  #9  
Old 30 July 2012, 06:07 PM
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Heavt breathing

To the extent that the air holds additional moisture, it will be much more able to take heat away from your body. All substances have a property called 'specific heat' which is the ability of that substance to absorb and release heat energy. The water molecule has one of the highest specific heat ratings, much higher than any other significant gas, due to its angular shape. As air gets colder, its ability to hold water as vapor decreases, until you get to where precipitation happens - the dew point. When air with a substantial amount of vapor blows across your skin, it absorbs heat more readily than very dry air. As noted above, very dry air is always dry - it just cannot hold much moisture.

Quote:
Originally Posted by Avril View Post
It always seems warmer to me if there's snow on the ground (to reflect the light, I assume)--how would this fit in?
That may be. Another factor is that the snow can get much colder than freezing temp readily, so it may be 'absorbing the cold' (technically, it would be rleasing its heat to the air right above it, making a layer near it which is not as cold as higher up), depending of course on the wind.

Quote:
Originally Posted by Alarm View Post
Around -40 Celsius, it no longer matters if it's dry cold or wet cold...
It also doesn't matter if you use Celsius or Fahrenheit at that temperature.
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  #10  
Old 30 July 2012, 06:41 PM
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I can tell you that a wet, cold winter in Florida feels far colder and more miserable than experiencing the same temperatures in other areas of the country. I don't know how much of that is psychological, but people from Northern climates have made similar comments to me.
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  #11  
Old 30 July 2012, 07:22 PM
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High relative humidity at high temperatures will interfere with the ability of a person to dump metabolic heat by sweating. This will tend to give a person a sensation of a higher air temperature, and actual higher skin temperature along with increased potential for overheating, than low relative humidity at the same temperature.

But if you're not sweating you're not much affected by the relative humidity of your environment. (Lower absolute humidity can cause dryness in tissues but this is unrelated to thermoregulation and furthermore isn't as easily and rapidly felt as high humidity at high temperature.) Unless you are actually getting liquid water onto your clothes or skin - i.e. you are in a supersaturated fog (>100% relative humidity) that is condensing on you, the humidity of the air should not have any direct physical effect on your body temperature nor your (blind) perception of heat or cold.

Quote:
Originally Posted by A Turtle Named Mack View Post
specific heat
?

Air at 0C and 100% relative humidity has a specific heat capacity around 0.5% higher than air at 0C and 20% relative humidity. It is completely negligible for these purposes.
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  #12  
Old 30 July 2012, 07:28 PM
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Quote:
Originally Posted by Richard W View Post
That doesn't make sense anyway. It doesn't really feel colder, it just feels as though it feels colder? Hmm...
To be fair, the claim is probably that somebody did experiments in a controlled chamber with different levels of humidity and temperature but all other factors the same, and asked people how warm or cold they felt, and didn't find a difference in perception with humidity because the factor that makes people feel colder when it's "wet cold" outside isn't the actual humidity. It's just that the way it was phrased makes it sound as though people don't really feel colder in the "wet cold" conditions.
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  #13  
Old 30 July 2012, 08:56 PM
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"Wet cold" - humid air has greater mass air flow and more cooling power, in the same way that moving air has more cooling capability (wind chill). It feels different and acts differently. Consider that the higher density of cold, humid air improves the performance of internal combustion engines because, well, there's more air transport.

Actual dampness also reduces the insulation value of warm clothing - wool is an exception to that but the moisture-wicking polypropylene underwear for skiing and other winter sports is much less effective when wet. This is a factor for areas with daytime rain and night-time temperatures below freezing. A thermometer won't bear this out, but a person standing in it will.
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  #14  
Old 30 July 2012, 10:55 PM
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Is this thing on?

Quote:
Originally Posted by Hero_Mike View Post
"Wet cold" - humid air has greater mass air flow
Humid air is less dense than dry air at the same temperature and pressure. Water molecules have less far less mass than nitrogen and oxygen molecules.

Quote:
and more cooling power
The volumetric heat capacity of air at 0oC at 100% relative humidity is about 0.3% more than that of air at 20% humidity. (Which is less than the *specific* heat capacity change I posted above because the more humid air is less dense.)

Last edited by Alchemy; 30 July 2012 at 11:03 PM.
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  #15  
Old 31 July 2012, 03:01 AM
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Absolute humidity, not relative. Yes, it's on.
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  #16  
Old 31 July 2012, 04:40 AM
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Isn't the reason simply that water particles both impart heat to the skin more readily than air and also evaporate, further cooling the skin?
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  #17  
Old 31 July 2012, 06:45 AM
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Quote:
Originally Posted by Alarm View Post
A wet cold glues your whiskers together, icing your mustache till you look like a walrus.
You are the walrus, coo coo ca choo.

Quote:
Originally Posted by Alarm View Post
Both kinds of colds are enough to freeze the brass balls off a canon ball bearing witch's monkey.

Is that the correct expression?

That it exactly
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  #18  
Old 31 July 2012, 09:08 AM
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Quote:
Originally Posted by Cervus View Post
I can tell you that a wet, cold winter in Florida feels far colder and more miserable than experiencing the same temperatures in other areas of the country. I don't know how much of that is psychological, but people from Northern climates have made similar comments to me.
My family have been to Florida twice during winter.
It is never cold in Florida!

I don't know what part of Florida you live in (or if that matters?) but is it possible that the reason you acutely feel a wet cold winters day in Florida is because of your own body conditioning?

For us, leaving here in mid winter for warmer air in southern Europe or Florida, makes the temperatures seem even warmer, as our bodies have already acclimatised to our damp cold winters.

Regarding the OP, personally I've felt warmer in places where it's a dry cold, but that's usually because those places are more likely to have a blue sky day, with sunshine during daytime. But at night time, the opposite is the case.
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  #19  
Old 31 July 2012, 01:20 PM
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Quote:
Originally Posted by jw View Post
For us, leaving here in mid winter for warmer air in southern Europe or Florida, makes the temperatures seem even warmer, as our bodies have already acclimatised to our damp cold winters.
This is it.

In '97, my wife and I went to California in January. The day we left Brandon, Manitoba, it was -35C. It was only +17C in Long Beach when we were there, but we were walking comfortably in shorts (as I would be today if it were only +17C).

You could tell the people from the north from the locals. We were in shorts!
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  #20  
Old 31 July 2012, 10:20 PM
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One Christmas my grown children came to visit. My daughter came out of her plane from Louisiana bundled up, saying, "Oh, it was so cold when I left. It was 50 !" An hour later her brother arrived from Colorado in shorts and a teeshirt, "Oh, it's been so warm! It was 50 when I left!"

Note: all times Farenheit, CO is dry, LA is damp. It was funny to me, anyway. Florida was warm and windy. Lovely.
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