Heat index facts for kids
The heat index (also known as humiture) tells us how hot it actually feels outside. It combines the air temperature with the amount of moisture in the air, called relative humidity. For example, if it's 32°C (90°F) with high humidity, it might feel like 41°C (105°F).
Your body normally cools itself by sweating. When sweat evaporates from your skin, it takes heat away. But when the air is very humid, sweat can't evaporate as easily. This means your body keeps more heat, making you feel hotter than the actual temperature.
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How the Heat Index Was Created
The heat index was first developed in 1978 by George Winterling. He called it "humiture." The National Weather Service started using it a year later. The idea came from earlier work by Robert G. Steadman.
The heat index uses some assumptions about people. These include things like body size, what clothes you are wearing, and how much you are moving. It also considers sunlight and wind speed. If these conditions are very different, the heat index might not perfectly show how hot it feels.
Heat Index vs. Humidex
In Canada, they use something similar called the humidex. The humidex is a bit different from the heat index. It uses the dew point instead of the relative humidity to calculate how hot it feels.
When is the Heat Index Used?
The heat index is usually calculated when the air temperature is above 27°C (80°F). It also needs the dew point temperature to be higher than 12°C (54°F). And the relative humidity must be higher than 40%.
It's important to know that heat index numbers are based on temperatures measured in the shade. If you are in direct sunlight, it will feel even hotter. Always take extra care when you are out in the sun.
Sometimes, the heat index and the wind chill are both called "apparent temperature." This term describes how hot or cold it feels outside.
Related pages
See also
In Spanish: Temperatura de bochorno para niños
