Felt Air Temperature

When you're outside in the summer or in the winter, sometimes it may feel warmer or colder than it really is because of either the humidity or the wind. If it is the summer, it is due mostly to the humidity, and in the winter, it is mostly the wind. The heat index is an attempt to combine the actual temperature and the humidity to a degree that the body perceives the temperature to be. Similarly in the winter, the wind chill is used to attempt to combine the actual temperature and wind speed to a degree that the body perceives the temperature to be.

Both of these are called Felt Air Temperature. It isn't how hot or cold the temperature is, but instead how it feels. The actual measurement is very scientific with a very long equation. However, both the wind chill and heat index make assumptions about the averages for people, including height, weight, clothing, body mass, amount of physical activity, thickness of blood, and sunlight and ultraviolet radiation exposure. The interesting thing about the heat index is that the higher the temperature goes, the less amount of humidity is needed to raise the heat index. For example, if it is 80°F, then the humidity has to be over 45% to raise the heat index above 80°F. But if the temperature is 110 °F, then the humidty needs to be over only 17% to raise the heat index over 110 °F. Similarly with wind chill, the colder the outside temperature is, the more the wind will affect the results.

Some other interesting facts about Felt Air Temperatures:

Because of the way humidity interacts with temperatures, haze then clouds would develop which reduces the amount of direct sunlight, so there was a maximum heat index that scientists thought would be possible on earth. This was 160 °F. However, on July 8, 2003, in Saudi Arabia, the dewpoint reached 95 °F and the actual temperature was 108 °F, which combined to be a heat index of 172 °F.

The coldest recorded wind chill varies, but the place doesn't. Vostok, Russia, in 2004: between -184°F to -192°F.

Canada doesn't use the heat index based on temperature and humidity. They use temperature and dew point, and they call it the humidex.

The wind chill had been used before World War II, but the heat index wasn't used until the late 1970's.

Bet you didn't know that!