Wind chill

Wind chill is the apparent temperature felt on the exposed human (or animal) body due to the combination of air temperature and wind speed. The wind chill temperature is always lower than the air temperature, even when the air is hotter than the body, because the wind increases the rate at which moisture evaporates from the skin and carries heat away from the body.

The concept is of particular significance in very cold climates such as the Arctic and Antarctic, at high altitude, at high speeds, or in very high winds. It is of great importance to the survival of humans and animals, and can even affect machinery and heating systems.

The official definition of windchill in meteorology was originally based on measurements taken at a distance above the ground. The exact definition of windchill has been controversial because it is a composite index, because animate and inanimate bodies behave differently, and because windchill reports have a major impact on winter tourism.

The first wind chill formulae and tables were developed by the United States military during World War II, initially by Siple and Passel working in the Antarctic, and were made available by the National Weather Service by the 1970s. In 2001 the formulae were revised to reflect more accurate theories and testing than those done by the military. These formulae are designed specifically for the human body, or even more specifically for the human face. Wind chill also affects animals, and wet, inanimate objects, but different formulae apply to them.

It has generally been conceded that the original model for windchill was not necessarily the best possible for all purposes. The physical basis for the calculation of windchill is now the relationship.