The heat index, or apparent temperature, combines air temperature and humidity to indicate how hot it feels to the body. High humidity slows sweating, the body's natural cooling system, making ...

Add Yahoo as a preferred source to see more of our stories on Google. "It's not the heat, it's the humidity." Actually, it's both, and that's where the National Weather Service's heat index comes in.

The heat index is a measure of how hot it really feels on your body when relative humidity is factored in with the actual air temperature. Since heat index values were devised for shady, light wind ...