Loss of heat from exposure of skin to wind. Heat loss is proportional to the speed of the wind. Thus, skin exposed to a wind velocity of 20 mph (32 km/hr) when the temperature is 0°F (— 17.8°C) is cooled at the same rate as in still air at — 46°F (-43.3°C). Similarly, when the temperature is 20°F (-6.7°C) and the wind is 10, 20, or 35 mph (16.1, 32.2, or 56.3 km/hr), the equivalent skin temperature is —4°, -18°, or — 28°F (-20°, -27.8°, or— 33.3°C), respectively.