Dennis Mahoney, age 15, of Rensselaer, New York, for his question:
What exactly is the wind chill factor?
The wind chill factor is a recent addition to the weather report. It is some
what mystifying because it is not based on provable scientific measurements. The weatherman can read the exact temperature from an unbiased thermometer. He can measure rainfall, wind strength and direction from other scientific instruments that have no personal opinions of their own. However, the wind chill factor includes an average human reaction to the weather.
On a calm day, chances are you can guess the outdoor temperature, nearly right on the button. But if a mild breeze is blowing, many people feel that things are a few degrees cooler than they really are. If a strong wind is blustering around, the average person may estimate the temperature to be as much as 20 degrees below what it actually is. This problem interested meteorologists working in the Antarctic, .back in 1939.
Many attempts were made to tie this wind chilling factor to a scale that would give the average person an idea how the weather is likely to feel, in spite of what the thermometer says. This was not easy because the average person is hard to find and various people react differently to the chilling effects of the wind. As a rule, plump people feel it less and skinny people feel it more. And anybody wearing thin or damp clothing shudders in a cold breeze. Meteorologists computed numerous opinions to chart the reactions of the average person.
This chart compares the true thermometer temperature with the velocity of the wind. For example, let's suppose that the actual temperature outdoors is 30 degrees F. The strength of the wind seems to reduce this by a specified number of degrees. If today's wind velocity is five miles per hour, the chill factor is three degrees. If it is ten miles, the chill factor makes it feel like 16 degrees F. A 20 hour wind makes a person feel that the 30 degrees F temperature is 4 degrees F.
Obviously, the system is based on the speed of the wind. It works because moving air removes body heat. In calm air, the normal heat produced by the body tends to hover near the skin, trapped in the clothing. A stiff wind removes this cocoon of body heat and replaces it with cooler air. This is why the chill factor from a blustery wind seems to penetrate right through to a person's bones.
It is nice to know what to expect from the weather when we step outdoors. Naturally a thermometer reading of ten degrees F would warn us to wear something warm. But it would hardly prepare us for the effects of a ten hour wind. At this velocity, the chill factor plunges 19 degrees. In other words, we should prepare to cope with a shivery temperature of minus nine degrees F, even though the thermometer insists on ten degrees F.