For those who don’t live near large bodies of water, few things are ever colder than the air temperature. That includes fingers, as well as thermometers and car engines. But, unlike objects, people can still get into trouble if their internal body heat ever drops below about 95 degrees. The situation is similar for all warm-blooded animals. And, the wind affects how quickly we lose internal heat. That’s why the National Weather Service developed the wind chill index – to chart the effect at various temperatures and wind speeds. The chart doesn’t factor in other things that can have an effect: the cloudiness, your clothes or your sensitivity to cold. Generally, though, the faster the wind, the faster we lose our self-generated heat. And, if the wind chill is at or below minus 18 degrees, we’d better watch out. Frostbite can occur within minutes.
Mary Knapp, Weather Data Library