Why do we have a ‘wind chill fac­tor’?

BBC Earth (Asia) - - Q&A -

On cold, windy days, weather fore­cast­ers often warn that the stated tem­per­a­tures are mis­lead­ing, as it will feel much colder due to ‘wind chill’. First de­vised in the 1940s, the wind chill fac­tor was based on the ef­fect of wind speed on heat-loss from cylin­ders of wa­ter. By the early 2000s, this had be­come the more ac­ces­si­ble con­cept of the dif­fer­ence in tem­per­a­ture re­sult­ing from ex­po­sure to the wind. So, for ex­am­ple, 4°C above freez­ing is said to feel more like -2°C in a 40km/h breeze. But the idea of wind chill can be mis­lead­ing. No mat­ter how hard the wind blows, it can’t chill things be­low air tem­per­a­ture – it sim­ply in­creases the rate of heat loss. Plus wind chill cal­cu­la­tions leave out key fac­tors such as the con­stancy of the wind and whether the Sun is shin­ing. RM

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