Heat index

The heat index (HI) is a measure of temperature as perceived by humans, combining actual air temperature and relative humidity, in shaded areas; it takes into account that elevated humidity makes hot ambient temperature feel higher than the same temperature with lower humidity, as evaporative cooling of sweat is less effective. For example, when the temperature is 32 °C (90 °F) but relative humidity is high at 70% it feels as hot as 41 °C (106 °F) at low humidity. The heat index relates to sensed temperatures in the shade without taking into account heating by direct sunlight and physical activity, or cooling by wind.

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Source: Wikipedia · Image: Wikimedia Commons · CC BY-SA 4.0

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