According to the National Weather Service in Des Moines, the HOTTEST day of this current heat wave will be Wednesday as the temps will hover around the mid-90s and heat index readings could be as high as 105*.

But WHAT exactly is a 'Heat Index?" How is it measured? According to the National Weather Service:

The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature.

When the humidity is high, evaporation of sweat from the body decreases, making your body feel warmer in humid conditions. (see chart below)

Credit: NWS Des Moines via Twitter