December 8, 1999


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Wind Chill

The combination of wind and low temperatures can produce much greater heat loss from exposed flesh than the air temperature alone would suggest. The figure often used in cold countries to express this is the wind-chill temperature.
Wind chill figures are based on experiments conducted in the Antarctic to estimate the risk of frostbite. When the wind-chill temperature is below -30 degrees Celsius, there is a real risk of flesh freezing, and when it is below -50, flesh will freeze in a minute or so.
In North America, where cold waves of the arctic air can suddenly sweep southward, these figures are used for warning people, of the dangers of going out. In warmer parts of the world, however, they can be misleading, especially when the temperature is above freezing. For instance, a combination of 4 degrees and a wind speed of 48 kph equates to a value of -11 degrees. At this figure, it is unlikely that anything will freeze; indeed bush walkers need to be on guard for although it may feel bitterly cold, snow will be thawing rapidly, and on steep, snowy slopes, the risk of avalanches may be extreme.


The Wind-chill table shows the apparent temperature produced by the combination of actual temperature and wind speed.

Heat and Humidity

In hot weather, the combination of heat and humidity determines the level of human comfort. This comfort factor can be described in terms of either the apparent temperature and relative humidity. When the apparent temperature is above 32 degrees, about half the population feels hot and sticky, and by the time it reaches 41 degrees most people feel uncomfortable. Summer heat waves with sustained above 41 degrees are dangerous and can increase the mortality rate.

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