What the f**k is it with the wind chill factor? If it feels like minus five degrees, shouldn't we just call it minus five degrees?
From Wikipedia
There is a thermal boundary layer surrounding the skin which may be several millimetres thick. This boundary layer acts as an insulator. When it is cold and the wind is blowing, the air feels colder than it does when it is calm because the wind blows away the boundary layer. In a perfect calm, if free convection could be suppressed (as it is in microgravity), the boundary layer would be infinitely thick. Add a wind, and the only still air that remains would be the air in the immediate vicinity of some surface, like the skin. The stronger the wind, the thinner the layer. Because the outer layers of still air are blown off more easily than the ones closer to the skin, when it is nearly calm, a small increase in wind speed causes a much greater thinning of the boundary layer thickness than the same increase in wind speed when the wind is already strong.
Convective heat loss is really conduction through an insulating boundary layer. The insulation of the boundary layer depends on its thickness. When there is wind, the thermal resistance of the boundary layer is smaller, the heat loss is higher, and the temperature of the skin is closer to the air temperature. Humans do not sense the temperature of the air but the temperature of the skin. Because skin temperature is closer to the air temperature when it is windy, the wind causes it to feel colder.[1]
A wind-chill factor of 25° F (- 4° C) will not freeze water if the air temperature is 35° F (2° C). Water changes state according to the temperature of the body of the water. In this case, the water and air temperature are about the same — too high to freeze water.[2]
