Wind Chill Index Chart

In 2001, NWS implemented an updated Windchill Temperature (WCT) index. The change improves upon the former WCT Index used by the NWS and the Meteorological Services of Canada, which was based on the 1945 Siple and Passel Index.

In the fall of 2000, the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM) formed a group consisting of several Federal agencies, MSC, the academic community (Indiana University-Purdue University in Indianapolis (IUPUI), University of Delaware and University of Missouri), and the International Society of Biometeorology to evaluate and improve the wind chill formula. The group, chaired by the NWS, is called the Joint Action Group for temperature Indices (JAG/TI). The goal of JAG/TI is to upgrade and standardize the index for temperature extremes internationally (e.g. Windchill Index).

The current formula uses 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.

Clinical trials were conducted at the Defence and Civil Institute of Environmental Medicine in Toronto, Canada, and the trial results were used to improve the accuracy of the new formula and determine frostbite threshold values.

Standardization of the WCT Index among the meteorological community provides an accurate and consistent measure to ensure public safety. The new wind chill formula is now being used in Canada and the United States.

Specifically, the new WCT index:

• Calculates wind speed at an average height of five feet (typical height of an adult human face) based on readings from the national standard height of 33 feet (typical height of an anemometer);
• Is 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; and
• Assumes no impact from the sun (i.e., clear night sky).

What is Wind Chill Temperature?

The wind chill temperature is the temperature that it feels like outside to people and animals. Wind chill is based on the rate of heat loss from exposed skin caused by combined effects of wind and cold. As the wind increases, heat is carried away from the body at an accelerated rate, driving down the both the skin temperature and eventually the internal body temperature. Therefore, the wind makes it feel much colder. If the temperature is 5 degrees Fahrenheit and the wind is blowing at 25 mph, the wind chill is -17 degrees Fahrenheit. With a wind chill temperature of -18 degrees Fahrenheit, exposed skin can freeze in 15 minutes.

What is frostbite?

Frostbite occurrs when body tissue freezes and damage to that tissue occurs. The most susceptible parts of the body are the extremities such as fingers, toes, ear lobes, or the tip of the nose. Symptoms include a loss of feeling in the extremity and a white or pale appearance. Medical attention is needed immediately for frostbite. The area should be SLOWLY re-warmed.