The Heat Index has been abused by media sources from its' intended purpose of helping prevent heat/cold injuries in order to sensationalize their news. Using the heat index by itself is not that great at preventing these injuries either as it is only one part of an equation.

This abuse has grown worse because of the global warming hoax, as the Al-Goreites are trying to use this to make it seem hotter then it really is.

Our Military has been quite sensitive to heat/cold stress injuries for decades, and in fact they (USN/USMC) are the ones that first came up with the forumla  in the mid 1950's at Parris Island MCRD.

In the military it is referred to as the WBGT for wet bulb globe temp. and is figured by using the actual air temp, wet bulb temp aka heat index, and the radiant temp (the temp reflected back from an object like concrete sidewalks etc etc etc).

Those of you that served may remember various colored flags being used at Boot camp to alert to possiblity of heat injuries and what actions are needed to prevent them.

There are other factors involved too, but I won't bore you anymore, but I spent many an hour crawling around engine rooms or on a grinder figuring out this little formula.

I will say though that heat warnings issued by local weather programs are done using the WBGT, but they all report the heat index.