What is the wind chill index (WCI)? The WCI, developed by physicist Paul Siple in 1939, indicates how cold it feels outside to a person. The WCI uses the ambient temperature and the wind speed to calculate how cold it will feel outdoors. The wind chill guideline is used by the National Weather Service and the American Red Cross.
The WCI is calculated from the wind speed and air temperature and is expressed as a number.
In other words, Wind Chill Index is the measurement of the effect wind has on how cold it feels to humans. Areas with higher humidity have lower wind chills because they keep you warmer, but areas with dry air have much lower wind chills because they are more efficient at cooling you off. One can use a table, chart, or the tool above for this measure so that people know what to expect in their area when the weather report suggests low temperatures.