The previous wind chill index was substandard when considering modern-day uses, according to most meteorologists, who sheepishly agree the method of calculation was less than ideal. The old index has been used by the National Weather Service since 1973 and was based on experiments studying the threshold for freezing water by Antarctic explorers in 1945. Because it measured freezing properties of water and not skin, applying the wind chill index to the human comfort level was far less than ideal.
The new index will address freezing thresholds based on the human body and will show frostbite danger at given periods of time.
In October 2000, scientists began developing the updated index using human volunteers at the wind tunnel and climatic chamber of the Defense and Civil Institute of Environmental Medicine in Toronto, Canada.
"The new wind chill index provides us with specific warning of time-to-frostbite at given levels of wind chill," said retired General Jack Kelly, director of NOAA's National Weather Service. "Since it is the responsibility of the National Weather Service to help protect lives, we believe this will be an important service to the American people during winters to come."
According to the NWS, 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
- Assume no impact from the sun (i.e. clear night sky).
"We're proud that the new index reflects the best science, technology and computer modeling technology," said Kelly. "For the first time, a consistent standard of wind chill will be used by both Canada and the United States."
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