As of Nov. 1, 2001, the National Weather Service (NWS) and the Canadian government have changed the way they measure Wind Chill Temperature (WCT). This new method will be used throughout all of North America and will produce much more realistic numbers and is designed to calculate how the cold feels to human skin.
Under the new method, the calculated wind chill will actually be warmer. The new measurement was designed to help people plan better for going outdoors knowing how to properly gear up for the cold. The new method also is the first time a frostbite danger index has been included as a part of the equation.
Heres an example:
At 11F with a wind speed of 20 mph, the WCT would be 23F under the old index. Using the new measurement method, the same conditions would provide a WCT of only 8F.
Why the difference? The new index accounts for wind speed at human face level and uses a new formula for calculating body heat loss. The National Weather Service had used the outdated Siple and Passel index since 1945. This index relied on measuring wind speed at 33 feet above the ground and focused on how long it took to freeze water at that wind speed and temperature.
In 2000, the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM) formed a group called the Joint Action Group for Temperature Indices (JAG/TI). The goal of the group was to internationally upgrade and standardize the index for temperature extremes (Wind Chill) for North America. Standardizing the wind chill index among the meteorological community will provide accurate and consistent measure to help assure public safety during the cold seasons.
The new index is based on:
This latest wind chill index, now used in the U.S. and Canada, was developed after extensive analysis of the factors that impact wind chill. It was developed using the latest advances in science, computer modeling and technology.
In 2002, adjustments based on possible impact of the sun may be added to the calculation. The new Wind Chill Index will, for the first time, show specific wind chill threshold values identifying frostbite danger at given periods of time.
Public Notification of New Windchill Temperature Index
Commonly Asked Questions
Sources Of Information
National Weather Service: http://www.nws.noaa.gov/
NOAA-National Oceanic and Atmospheric Administration: http://www.nws.noaa.gov/om/winter/
University of Colorado http://www-nsidc.colorado.edu/NSIDC/EDUCATION
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