What is the new formulaused for calculating wind chill?
Most people know about wind chill: the temperature your body feels when it is
exposed to a certain air temperature combined with a particular wind speed. The high-
er the wind speed, the “colder” the wind chill temperature and the faster the exposed
areas of a person’s body will lose heat (a process known as transpo-evaporation; when
moisture evaporates, the surface from which it evaporates loses some heat).
The newest wind chill chart—called the Wind Chill Temperature Index—took
over from the old chart (developed in 1945) in the 2001–2002 winter season. The rea-
son for the change was simple: The original wind chill index revolved around heat
loss, with a standard set at the chill experienced while standing outside in air moving
4 miles (2 kilometers) per hour. Based purely on temperature and wind—and on how
water freezes in plastic containers—the charts were developed in Antarctica by Paul
Siple and his fellow explorer, P. F. Passel, back in 1939, partly with the intention of
being used in World War II battlefield planning.
Not everyone was thrilled with this simplistic, two-factor interpretation, however.
There were pieces missing from the wind chill puzzle, such as the fact that humans
constantly generate heat to the lack of wind measurements above 40 and below 5 miles
per hour (64 and 5 kilometers per hour). Passel and Siple’s wind speeds were also taken
about 33 feet (10 meters) above the ground, making the chart more valuable for a
third-floor office than ground level. But the biggest problem overall was that the old
wind chill chart could not accurately predict how humans perceive temperature.
Thus, the new wind chill index was created. This chart includes such changes as
wind speeds calculated at the average height of a human head (about 5 feet [1.52
meters] above the ground); it is based on a human face model and sundry other more
“modern” considerations. The actual general formula for the wind chill has now
changed to the following: Wind chill in degrees Fahrenheit 35.74 0.6215T
35.75(V0.16) 0.4275(V0.16), in which T is the air temperature (in degrees Fahrenheit),
and V is the wind speed (in miles per hour).
The biggest difference between the old and new indexes is that the new index usu-
ally registers warmer temperatures than the old index. Still, no matter what the equa-
tion or chart, when temperatures are icy cold and winds are high, everyone should be
careful and bundle up.
Calculating the Wind Chill
Wind Speed (mph)
0 5 10 15 20 25 30 35 40 45 50 55 60
40°F 36°F 34°F 32°F 30°F 29°F 28°F 28°F 27°F 26°F 26°F 25°F 25°F
35°F 31°F 27°F 25°F 24°F 23°F 22°F 21°F 20°F 19°F 19°F 18°F 17°F
30°F 25°F 21°F 19°F 17°F 16°F 15°F 14°F 13°F 12°F 12°F 11°F 10°F^309