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On November 1, 2001 the National Weather Service will implement a "new and improved" wind chill temperature (WCT).  The original index was based on empirical data developed in 1939 by Antarctic explorers Siple and Passel and has long been thought by the meteorological community to have been too simplistic and to have overstated the overall cooling effects of the wind.  To address this, the National Weather Service has developed a more modern model that makes "use of advances in science, technology and computer modeling to provide a more accurate, understandable and useful" WCT.  Some of the key changes in the new Wind Chill Index will include:
  • making an adjustment for the calculated wind speed which is typically measured at 33 feet (i.e., 10 meters) to reflect the wind at a "face level" of 5 feet.
  • using a more up to date model of the human face.
  • taking into account modern heat transfer theory for heat loss from the body to its surroundings;
  • lowering the calm wind threshold from 4 mph to to 3 mph.

In 2002 a further adjustment is planned to account for the affects of solar radiation due to cloudy, partly cloudy or clear skies.

For comparison Figures 1 and 2 show the differences in the indices given constant temperature (Fig. 1) and or constant wind speed (Fig. 2).  (click to enlarge)

Fig 1.        Fig. 2

Figures 3 and 4 shows the complete "New" and "Old" Wind Chill Charts.


Figure 3.

Figure 4.

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