On November 1, 2001 NWS implemented a replacement Wind Chill Temperature (WCT) index. The change improves upon
the current WCT Index used by the NWS and the Meteorological Services of Canada (MSC, the Canadian equivalent of the NWS),
currently 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).
JAG/TI's goal is to upgrade and standardize the index for temperature extremes internationally (e.g. Wind Chill 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
- Assumes no impact from the sun (i.e., clear night sky).