Wind Chill

Click here for a Wind Chill Calculator and Chart.

The NWS implemented a new Wind Chill Temperature (WCT) index in late 2001. The reason for the change was to improve upon the old WCT Index used by the NWS and the Meteorological Services of Canada (MSC, the Canadian equivalent of the NWS), which was based on the 1945 Siple and Passel Index.  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 was to internationally upgrade and standardize the index for temperature extremes (e.g., Wind Chill Index).

Wind Chill Chart

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 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. In addition, clinical trials were conducted and the results of those trials were used to verify and improve the accuracy of the new formula. Standardization of the WCT Index among the meteorological community was important, so that an accurate and consistent measure is provided and public safety was ensured.

Specifically, the new WCT index will:

  • use wind speed calculated at the average height (5 feet) of the human body's face instead of 33 feet (the standard anemometer height);
  • 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 the worst case scenario for solar radiation (clear night sky).

    For example, assuming an air temperature of 5 degrees and a wind of 30 mph... Old WCT = -41 New WCT = -18

    National Weather Service Forecast Offices have adjusted the threshold values of Wind Chill Temperatures that trigger Wind Chill Advisories and Wind Chill Warnings, to reflect the new formula.

    Here's the formula:

    Wind Chill (F) = 35.74 + 0.6215T - 35.75(V0.16) + 0.4275T(V0.16)
    Where V = the wind speed value in mph and
                 T = the temperature in F

    Note: Frostbite occurs in 30 minutes or less at wind chill values of -18 or lower

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