The heat index is an invention of weatherman George Winterling, used to describe what the ambient temperature "feels like" based on a number of assumptions. Liberals use these inflated temperatures to push their global warming agenda.
The heat index was adopted for use by the government run National Weather Service. It relies on a number of assumptions about clothing, height, weight, health and UV exposure which are not always applicable. The heat index does not factor in the cooling effects of wind.
The heat index has been used in an attempt to obfuscate the evidence against global warming. The lamestream media often reports the heat index "temperature" as if it were the real temperature.