This chart shows you the Heat Index…which is the temperature your body is reacting to regardless of the actual air temperature. Obviously the drier the air, the easier it is on your body to handle the heat. Depending on your physical condition & level of hydration, the indices in the white range can be tolerated well if you pace yourself. The beige, yellow, orange, and red indices are where even the most physically fit and well hydrated people can get into trouble very, very fast. If you’re in doubt, pace yourself, stay very well hydrated, and don’t forget the sunscreen. Those UV rays will wreck havoc on your skin.