What is the definition of windchillfactor?

Answer 1

Wind chill factor is a measure of the effect of wind on heat loss in exposed skin. In most environments, the human body's temperature is higher than that of the surrounding air. Where the weather is significantly cold, exposed skin heats a layer of air around it which insulates the skin from heat loss. However, a wind will blow the warmed air away from the skin and replace it with cold air. The laws of thermodynamics dictate that you lose heat energy faster the colder the thing that is draining it.

Heat loss through evaporation is also a factor in increased heat loss when there is a wind.

Wind chills were at one time expressed in terms of the amount of heat lost per second or minute, but people had a hard time understanding that. Nowadays it is more often expressed as a temperature, which is easy to understand, but is misleading. So you will hear "The temperature is twenty below zero but with the wind chill it is forty below", it means that because of the wind, you will lose as much heat from exposed skin as you would on a windless day where the temperature is forty below. As a result, your exposed skin will take the same amount of time to freeze. However, the temperature is still twenty below for all purposes other than calculating heat loss. The brittleness which affects steel at forty below does not happen unless the actual temperature is forty below, for example.