Why Damp Weather Makes Us Feel Colder
Our clothing keeps us warm on cool days by trapping air between our bodies and clothing. The clothing, and layer of trapped air, prevents our bodies from losing heat by convection currents, which transfer heat by circulating air like a cool breeze on a hot day. Air trapped by clothing cannot easily circulate to transfer heat and cool our bodies. The body must first warm this layer of trapped air to keep us feeling warm. On a very cool damp day, however, this layer of trapped air contains water molecules. If it is damp, our clothing is also likely to contain some water molecules. It takes more heat energy to warm water than air.
In physics parlance, water has a higher specific heat capacity than air. If the layer of air next to the skin is damp, it therefore takes more of the body’s heat energy to warm it. Hence the perceived temperature is cooler.
Why Humidity Makes a Hot Day Feel Hotter
Moisture in the air contributes to your body’s cooling processes. Image by coniferine
It helps to first understand why high humidity on a hot day makes the perceived temperature higher. Sweating is a cooling mechanism. When the humidity is low, sweat evaporates easily. Evaporation requires thermal (heat) energy, so evaporation is a cooling process. When our sweat evaporates it cools our bodies. On a hot humid day, sweat does not evaporate as easily, so the body’s cooling mechanism does not work as well. The limited evaporation in humid conditions is not enough to cool the body.
When it is cool and humid, the body does not need a cooling mechanism, so the body sweats less. The high humidity does not therefore limit evaporation to keep the body warm as it does on a hot humid day. Additionally, on a cool dry day, the low humidity does not increase the body’s cooling rate as it does on a hot dry day because most people do not sweat significantly when it is cool.
Therefore the mechanism that causes a humidity to make a hot day feel hotter does not apply in cool weather.
Why Dampness Makes a Cool Day Feel Colder
On a cold rainy day the falling rain soaks our clothing to make us feel colder. On a cool damp day, it is less obvious, but our clothing can also absorb some moisture from either the damp air or our bodies. Whether it is raining or simply damp, wet clothing does not keep us as warm as dry clothing for a few reasons.
In cold weather, high humidity levels will make you feel colder. Clothing keeps your body warm by trapping a small layer of warm air around you. Your own body temperature warms the air, but your cozy sweatshirt is what keeps it close.
If the air is humid, it has a high water content. It’s more difficult to transfer your body heat to water than it is to air. As mentioned previously, the process of moisture evaporating off your skin naturally cools you down. Your body won’t sweat when it’s cold, but humidity from the air can place moisture on your skin and give you the same chilly effect.
If the humidity levels are extremely high, the moisture can saturate your clothing. This leaves chilled water molecules against your skin and makes a cold environment feel even chillier. High humidity and cold weather will leave you feeling colder than if humidity levels were low.
This is why truly wicking fabrics like wool keeps you warmer than any synthetic fabric on the market, no matter how ‘wicking’ it is labeled.