Understanding Wind Chill

FEELING THE COLD: THE SCIENCE OF WIND CHILL A. Anyone who has waited for a bus on a breezy January morning knows that wind can make cold weather feel much worse. Weather forecasters in Canada express this effect through the wind chill index, a number that describes how cold the air feels on exposed skin. The index is reported in units that resemble degrees Celsius, but it is not an actual temperature. A thermometer left outside in the wind will not drop below the true air temperature, no matter how strongly the wind blows, and water will not freeze simply because the wind chill is below zero. The index was developed by scientists who studied how quickly the face loses heat in cold, windy conditions. Forecasts often include both figures, so that people can plan how to dress. B. The science behind wind chill concerns the thin layer of warm air that surrounds the body. On a calm day, this layer acts as a kind of insulation, slowing the loss of heat from the skin. When the wind blows, it strips this layer away and replaces it with colder air, so the body loses heat more quickly. The stronger the wind, the faster this happens. That is why a day of minus ten with a strong wind can feel as uncomfortable as a still day that is far colder. Wet skin and damp clothing make matters worse, since water carries heat away from the body far more quickly than dry air does. C. Wind chill matters because exposed skin can freeze surprisingly fast. At extreme wind chill values, frostbite can develop on the cheeks, nose, ears and fingers within minutes. Early signs include redness and a pins-and-needles feeling, followed by numbness and skin that looks white or greyish. Health authorities advise people who notice these signs to move indoors and warm the area gradually with lukewarm water rather than rubbing it, since rubbing can damage frozen tissue. Anyone whose skin stays numb or blisters should seek medical care. Hypothermia, a dangerous drop in the body's core temperature, can also occur when people spend long periods outdoors without proper clothing. D. Forecasters issue cold warnings when wind chill is expected to reach dangerous levels, with thresholds that differ between regions because people in the far north are more accustomed to severe cold. During such warnings, people are encouraged to dress in several loose layers, cover as much skin as possible and limit their time outdoors. Pets and outdoor workers need attention too. Some employers adjust schedules or provide heated shelters, and many cities open warming centres for people experiencing homelessness during the coldest nights of the year. Schools may keep students indoors at recess, and some outdoor events are postponed until conditions improve.