Why damp days feel colder

Yesterday, I exp l a in ed wind chill. I did so to get to a question that Kevin Redmond submitted late last month. Kevin understands the concept of wind chill but wonders why the humidity is not reflected in the perceived temperature using current wind-chill metrics.

It certainly does feel colder on a damp day, Kevin; here’s why.

Our clothing keeps us warm by trapping air between our body and our clothes. Our body then warms this thin, layer of air. The air trapped can’t easily circulate to transfer heat and cool our bod- ies. On a cool damp day, however, the layer of air trapped between you and your clothes contains more water molecules. It takes more heat energy to warm water than it does to warm air because water has a higher heat capacity. If the layer of air next to your skin is damp, it will take more of the body’s heat energy to warm it. That transfer of heat from the body to the air will cool you down.

Sky condition is another factor. A damp day is almost always overcast. On a dry sunny day, your body is more likely to be warmed by the sun.

The factors such as cloud cover, where individuals happen to be and moisture trapped in a layer of air between clothing and a body can be measured but on an individual basis. Too many variables exist to make this a calculated value that’s added to a forecast to keep people safe.

So Kevin is correct, it does feel colder on a damp day but that’s not what wind chill is measuring. Wind chill is a value that indicates the perceived temperature of exposed skin cooled by the wind. As wind speeds and temperatures fluctuate, so do the calculated values or feel-like temperatures.

Did you know … a recent survey indicated 82 per cent of Canadians use wind-chill information to decide how to dress before going outside in the winter.