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I sometimes hear stories where people compare their feelings in winter in different places in the world.

It goes like

in city X the temperature was the same as in city Y, but the humidity made me feel much colder...

or

oh well, -20°C would be cold, but the humidity was low, so it felt OK

so it implies that humidity somehow makes it feel colder. I am talking about temperatures below freezing (-30...0°C).

Does this have any physical explanation, or is it some sort of psychological phenomenon?

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  • $\begingroup$ At the same time humidity makes warm air feel warmer, because by limited evaporation you don't release your heat by sweating. I was always curious where is the break through temperature? If we ignore sweating and other factors and use conductivity factor alone the break through temperature would be our body temp ~ 36.6C. $\endgroup$ – NeverEndingQueue Sep 2 '18 at 5:54
  • $\begingroup$ I've become more convinced that the effect may be more to do with air density in general. Where I live at 1000m above sea level we don't notice a 'humid cold'. But when I go to the coast, boy it's colder at 0C than home at -10C. The mass of air in a cubic meter (1.0kg) is significantly higher at sea level (1.3kg), I suspect that trumps the few extra grams of water for conduction. $\endgroup$ – Arunas Feb 12 '19 at 3:44
  • $\begingroup$ According to the table here, the difference in density between sea level and 1000 m altitude is about 10%. But yes, I agree that it seems to be a significant factor. $\endgroup$ – user27542 Feb 12 '19 at 8:34
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Various types of apparent temperature have been developed to combine air temperature and air humidity. For higher temperatures, there are quantitative scales, such as the heat index. For lower temperatures, a related interplay was identified only qualitatively; e.g., in a 2012 textbook:

High humidity and low temperatures cause the air to feel chilly

Or in The Columbia Electronic Encyclopedia

Cold air with high relative humidity "feels" colder than dry air of the same temperature because high humidity in cold weather increases the conduction of heat from the body.

Or in Popular Mechanics:

There has been controversy over why damp cold air feels colder than dry cold air. Some believe it is because when the humidity is high our skin and clothing become moist and are better conductors of heat, so there is more cooling by conduction.

A useful concept is thermal comfort, which considers many other factors, such as skin wetness and cloth friction. (I've started a section at Wikipedia).

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    $\begingroup$ That last one seems credible: when temperature drops and reaches the dew point, water will condensate on surfaces, including clothes. Damp clothes will cause extra heat loss, not just because of better conduction, but also because that moisture can evaporate again when coming in contact with the warmer (relatively dryer) air between the layers of clothing. $\endgroup$ – Previous Jun 3 '16 at 3:28
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Higher humidity means that their is a larger concentration of water in the air. Water has a higher specific heat compared to oxygen gas, thus it is able to more easily give off heat (or take it away in the case of something feeling cold).

An everyday example of this is how diving into a pool that's just above 0 degrees Celcius feels much much colder than being outside in 0 degrees. Similarly cold air with high humidity will reduce the temperature of our bodies faster than air with low humidity. And, hot air with high humidity will increase the temperature of our bodies faster than air with low humidity.

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    $\begingroup$ water (liquid or vapor) also has higher thermal conductivity than air $\endgroup$ – hyportnex Feb 5 '14 at 16:29
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    $\begingroup$ I don't think this answer is correct - (i) unless you are in a small, enclosed space the heat capacity of the air is not very relevant (motion of air currents will take any warmer air heated by your body away from you faster than it can heat up significantly), (ii) the thermal conductivity or the air is more relevant, but the thermal conductivities of moist and dry air are virtually the same at these temperatures. $\endgroup$ – Mark A Jun 3 '16 at 1:50
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    $\begingroup$ @user27542 At 0°C and 100% humidity, there would be less than 0.5% water vapor in air ( 4.8 g/m³, and a cubic meter of air weighs about a kilogram). $\endgroup$ – Previous Jun 3 '16 at 2:27
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a lot of humidity means a lot of water vapors in air and water has a lot of thermal capacity(heat needed to raise 1'C of substance) compared to air.This means that surrounding air will take more heat to warm up and therefore will make you feel cooler.

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Also, at lower temperatures the air cannot hold as much water vapor so lower temperatures may not feel as cold as higher temperatures.

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Insulation, insulation, insulation! Your body is constant +36C. Your clothes are insulators. If air humidity gets higher, clothes insulation gets lower and you feel colder. Just wear humid tight outer one.

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