by Caleb, KE0FOE
The heat index is a value that combines air temperature and dew point in shaded areas as an attempt to determine the equivalent temperature felt by humans.
Heat is normally removed from the body by the evaporation of perspiration. Higher dew points reduce the rate of evaporation thus slowing the body’s ability to cool itself.
Because heat index values are measured in the shade, activity in direct sunlight can often yield even higher perceived values.
Heat indices here in Missouri this weekend have reached as high as 113 degrees. The highest calculated heat index in the world happened in Saudi Arabia in 2003. That’s when a temperature of 108 degrees along with a dew point of 95 degrees yielded an astounding heat index of 178 degrees!
Below is a chart allowing you to calculate the Heat Index when both air temperature and relative humidity are known.