"THE only argument against an east wind," said the American poet James Russell Lowell, "is to put on your overcoat". Lowell would have known nothing of the concept of wind chill, since the term was not conceived until 1939, but he was obviously familiar with the general idea that with low temperatures, the stronger the wind, the colder it seems to feel.
Even very low temperatures are quite bearable in calm conditions. You feel relatively comfortable because a layer of nearly motionless air encapsulates your body its innermost layers adapt to the body temperature and the envelope insulates you like the "dead air" space between the panes of a double glazed window. When a breeze develops, however, it disturbs and ultimately blows away this insulating layer and thereafter each molecule of air carries away with it the heat it gathers as it touches you.
Used sensibly and appropriately, the concept of "wind chill equivalent temperature" as often used in the media, can be a useful one. Its popularity stems largely from the fact that at a superficial level it is very easy to understand. We have all felt chilled by a stiff breeze when standing in the cold and it is nice to be able to put a number on the extent of our discomfort.
It is appropriate enough to think in terms of wind chill in circumstances where humans or animals are exposed to the relevant conditions, or when studying the problem of heat loss from buildings in cold weather. Indeed the concept of wind chill can be applied in any situation where warm objects are exposed simultaneously to both wind and low temperatures. Quite simply, the cold wind carries the heat away.
But it is wrong to apply the concept to unheated, inanimate objects. The temperature of the radiator of a car, of an oil storage tank, or of growing plants if they are dry will not drop below the local air temperature no matter how strongly the wind blows. If they happen to be wet, their temperature may drop slightly below that of the surrounding air, because of heat lost through evaporation, but the concept of wind chill in such cases is quite meaningless.
Wind chill also has ambiguities as far as humans are concerned. The extent to which we feel the cold depends on many other things besides wind and temperature. It varies depending on the amount of clothing we have on, on how old we happen to be, and on our physical, and indeed mental, condition at the time.