Wind Chill is the term used to describe the rate of heat loss on the human body resulting from the combined effect of low temperature and wind. As winds increase, heat is carried away from the body at a faster rate, driving down both the skin temperature and eventually the internal body temperature.

While exposure to low wind chills can be life threatening to both humans and animals alike, the only effect that wind chill has on inanimate objects (such as vehicles) is that is shortens the time it takes the object to cool to the actual air temperature (it cannot cool the object below that temperature). For example, water freezes at 32 degrees, regardless of what the wind chill temperature is.

The National Weather Service (NWS)  has implemented a replacement Wind Chill Temperature (WCT) index for the 2001/2002 winter season. The reason for the change was to improve upon the current WCT Index used by the NWS and the Meteorological Services of Canada (MSC, the Canadian equivalent of the NWS) that was based on research and an index from 1945.

The new formula makes use of advances in science, technology, and computer modeling to provide a more accurate, understandable, and useful formula for calculating the dangers from winter winds and freezing temperatures. In addition, clinical trials have been conducted and the results of those trials have been used to verify and improve the accuracy of the new formula. The new WCT incorporates the following factors:

• Calculates wind speed at the average height (5 feet) of the human body´s face instead of 33 feet (the standard anemometer height)
• Based on a human face model
• Incorporates modern heat transfer theory (heat loss from the body to its surroundings, during cold and breezy/windy days)
• Lowers the calm wind threshold to 3 mph
• Uses a consistent standard for skin tissue resistance
• Assumes the worst case scenario for solar radiation (clear night sky).

In 2002, adjustments for solar radiation (i.e., the impact of sun) for a variety of sky conditions (sunny, partly sunny and cloudy) will be added to the calculation model.