Why wind puts a chill in the air
We all know how much colder it feels in the winter when the wind is up!
Wind chill is a value that’s calculated based on air temperature and the wind’s speed, to get a better idea of how cold is really feels.
By definition, wind chill is the lowering of body temperature due to the passing flow of lower temperature air.
On a calm day, our bodies insulate us from the outside temperature by warming up a thin layer of air close to our skin. When the wind blows, it takes this protective layer away. It takes energy for our bodies to warm up a new layer and, if each layer keeps getting blown away, our skin temperature will drop – making us feel colder. Wind also makes you feel colder by evaporating any moisture on your skin – a process that draws more heat away from your body. This process is known as the cooling effect of evaporation. You can put that process to the test: take a cotton ball and wet it with alcohol. Rub it on your skin and notice how cold the affected area feels.
In a nutshell, wind chill is a value that indicates the perceived temperature of exposed skin. With this in mind, you can see how wind chill does not have this same effect on inanimate objects. Objects like metal or plastic, cannot be cooled beyond the temperature of the air, regardless of wind chill.
Last week I received a letter from Kevin Redmond. Kevin contends humidity should be included when calculating wind chill: “People talk of dry cold being so much ‘warmer’ than the damp cold and based on our experience in the north this is so accurate, yet that is not reflected in the perceived temperature using current wind-chill metrics.” So why is humidity not included in this calculation? Find out in tomorrow’s “Weather University.”