NOAA 2001-111
Contact: Curtis Carey

New Formula Will Provide More Accurate Warnings for North America

The National Weather Service, an agency of the Commerce Department's National Oceanic and Atmospheric Administration, will implement a new method to compute wind chill temperature to provide better winter weather warnings throughout the nation beginning Nov. 1, 2001. For the first time, the index will include specific wind chill threshold values showing frostbite danger at given periods of time.

"We're proud that the new index reflects the best science, technology and computer modeling technology," said retired General Jack Kelly, director of the weather service. "For the first time, a consistent standard of wind chill will be used by both Canada and the United States."

The new wind chill formula is the product of a year-long effort by scientists and wind chill experts from the academic community, and the U.S. and Canadian governments. This working 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).

In October 2000, scientists began evaluating the previous wind chill formula and developed plans for a standardized index among the meteorological community for North America. This new wind chill formula was developed after extensive analysis of the factors that impact wind chill, using the latest advances in science, technology and computer modeling to provide a more accurate, understandable and useful model for calculating the dangers from winter winds and freezing temperatures. The resulting formula was then tested using human volunteers at the wind tunnel and climatic chamber of the Defense and Civil Institute of Environmental Medicine in Toronto, Canada.

Specifically, the new wind chill 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 has been incorporated into the latest software build installed on the weather service Advanced Weather Interactive Prediction System (AWIPS) effective Nov. 1, 2001. In 2002, adjustments for solar radiation (the impact of the sun) and for a variety of sky conditions (sunny, partly sunny and cloudy) may be added to the calculation model.

"The new wind chill index provides us with specific warning of time-to-frostbite at given levels of wind chill," Kelly said. "Since it is the responsibility of the weather service to help protect lives, we believe this will be an important service to the American people during winters to come."

The previous index has been used by theweather service since 1973, and was based on science produced by Antarctic explorers in 1945.

The new wind chill index is available online at

The National Weather Service is the primary source of weather data, forecasts and warnings for the United States and its territories. The weather service operates the most advanced weather and flood warning and forecast system in the world, helping to protect lives and property and enhance the national economy.

To learn more about weather service, please visit

Media Note: A video news release on the new wind chill index will be available via satellite Nov. 2 at the times and coordinates listed below.

For more information contact Susan A. Weaver at 301-713-0622.
Satellite Coordinates: Nov. 1, 2001 at 12:45 p.m. - 1:00 p.m. EST
Satellite: PANAMSAT
Transponder: SBS6-04
Band: Ku
Downlink Frequency: 11798 MHz (V)
Audio: 6.4 and 6.8