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Wind Chill


Wind Chill Terms and Definitions

National Weather Service plans to Implement a New Wind Chill Temperature Index

Wind Chill Chart, use calculator at bottom of page to find wind chill

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Wind Chill Calculator

The NWS is planning to implement a replacement Wind Chill Temperature (WCT) index for the 2001/2002 winter season. The reason for the change is to improve upon the current WCT Index used by the NWS and the Meteorological Services of Canada (MSC, the Canadian equivalent of the NWS), which is currently based on the 1945 Siple and Passel Index.

For over a year, there has been discussion within the NWS and MSC about updating the WCT. During the Fall of 2000, the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM) formed a special group consisting of several Federal agencies, MSC, the academic research community (Indiana University-Purdue University in Indianapolis (IUPUI), University of Delaware, and University of Missouri), and the International Society of Biometeorology to evaluate the existing wind chill formula and make necessary changes to improve upon it. The group is called the Joint Action Group for temperature Indices (JAG/TI) and is chaired by the NWS The goal of JAG/TI is to internationally upgrade and standardize the index for temperature extremes (e.g. Wind Chill Index).

After the October 2000 and February 2001 meetings, the JAG/TI reached agreement on a new wind chill formula, discussed a process for scientific verification of the new formula, and developed plans for implementation of the new formula. The new WCT index was presented at the JAG/TI meeting in Toronto, Canada on August 2, 2001.

The JAG/TI formula will make use of advances in science, technology, and computer modeling to provide a more accurate, understandable, and useful 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.

Standardization of the WCT Index among the meteorological community is important, so that an accurate and consistent measure is provided and public safety is ensured. Our goal is to implement the new wind chill formula in Canada and the United States during the same time frame in order to have a consistent WCT Index for North America.

Wind Chill Temperature Comparison (Old vs. New)

 

Specifically, the new WCT index will:

  • use calculated 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);
  • be based on a human face model;
  • incorporate modern heat transfer theory (heat loss from the body to its surroundings, during cold and breezy/windy days);
  • lower the calm wind threshold to 3 mph;
  • use a consistent standard for skin tissue resistance; and
  • assume no impact from the sun (i.e. clear night sky).

The new formula will be incorporated into the latest software build installed on the NWS Advanced Weather Interactive Prediction System (AWIPS) by November 2001.

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.

Wind Chill Calculator

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Index Index


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Author: Mark Tew
Webmaster: Mike Gerber
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Last Updated: September 4, 2001