Why do windy winter days seem so bitterly cold? A winter day with a strong wind can seem much colder than one with only a mild wind, though the air temperature may be exactly the same. The effect that wind has on our perception of cold is called the wind chill factor. The greater the wind speed, the faster we lose body heat. Wind chill can make a fairly moderate winter day equivalent to a much colder one—sometimes dangerously so. For example, a day with a temperature of 30 ° Fahrenheit might seem of little concern, but combined with winds of 10 miles per hour, it can feel like it's only 21° Fahrenheit.
Wind chill is the popular name used to describe what cold WEATHER feels like at various combinations of low temperature and high WIND. The loss of body heat increases with a rise in wind speed, so that at the same temperature, a person will feel colder when the wind is blowing than when it is not. The effect of wind is to lower a person's temperature by evaporating moisture on, and blowing heat away from, the skin. Inanimate objects that have no heat to lose - a mail box or metal fence, for instance - are not really affected by the wind at all.
The more pronounced the air movement (wind or moving air produced by walking, skiing or riding in a convertible) and the greater the temperature difference between the surface of the object and the air, the greater the heat loss. Wind cooling is what happens when you blow on a mug of steaming hot chocolate to cool it to room temperature. But you cannot make it colder than that, no matter how hard you blow. Likewise, no matter how strong the wind blows, it cannot lower the temperature below that of the surrounding air. Of course, the hot chocolate would cool down to room temperature in any case, the blowing simply speeds up the process