WINDCHILL

also spelled Wind Chill, also called Windchill Factor, measure of the cooling power of the air on bare skin in relation to temperature and wind speed. Windchill can be expressed by various formulas, one of which is: wherein K is the heat (in kilogram calories) lost by one square metre of skin in one hour, v is the wind speed (in metres per second), t is the air temperature (in degrees Celsius), and it is assumed that normal bare skin temperature is 33 C (91.4 F). Many other variables that significantly affect heat loss, such as humidity and individual metabolism, are not considered. For example, sweating and rapid movements such as downhill skiing increase the cooling power, whereas bright sunshine decreases it. Windchill can be used to derive a windchill equivalent temperature Tei.e., the air temperature at a standard wind speed that would produce the same heat loss as the given temperature and wind speed. For example, 1.79 m/s (4 mile/h)about the speed of the wind generated by a person walking brisklyis a common standard wind speed. Then, for wind speeds above 1.79 m/s and less than about 20 m/s (45 mile/h), Te = 33 - (K/22.04). Thus, an air temperature of 0 C (32 F) would feel like -9 C (16 F) if the wind speed were 5 m/s (11 mile/h), -15 C (5 F) if the wind speed were 10 m/s (22 mile/h), -18 C (-0.4 F) if the wind speed were 15 m/s (34 mile/h), and -20 C (-4 F) if the wind speed were 20 m/s. Higher wind speeds do not produce significant additional windchill.