What is wind chill?

If you take any warm object and expose it to cold air, that object will lose heat to the air. The rate at which the heat is lost depends on two things – both the amount of temperature difference between the object and the air – and also the motion of the air.

The greater the temperature difference – and the faster the air movement – the greater the heat loss. And that heat loss is what we call wind chill. The term was coined by an Antarctic explorer, Paul Siple, in his 1939 doctoral dissertation.

But is there a “chill” effect of a 20-mile-per-hour wind at 100 degrees F.? Forecasters don’t call it a “chill” at that temperature – but it is the same effect whereby a breeze makes a hot day more tolerable.

Also – if you have a bowl of water out in 36-degree air but the wind chill is 24 degrees, will the water freeze? In this case, the answer is no. A container of water will lose heat to the surrounding air until it reaches the same temperature as the air. Wind chill will get it there faster, but won’t make it any colder in the end. So a bowl of water in 36-degree Farenheit air – in a stiff wind – won’t freeze.

October 29, 2009

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