The apparent temperature is a measure of relative
discomfort due to combined heat and high humidity. It was developed by R.G. Steadman
(1979) and is based on physiological studies of evaporative skin cooling for various
combinations of ambient temperature and humidity. The apparent temperature equals the
actual air temperature when the dew-point temperature is 57.2F (14C). At higher
dew-points, the apparent temperature exceeds the actual temperature and measures the
increased physiological heat stress and discomfort associated with higher than comfortable
humidities. When the dew-point is less than 57.2F, on the other hand, the apparent
temperature is less than the actual air temperature and measures the reduced stress and
increased comfort associated with lower humidities and greater evaporative skin cooling.
Apparent temperatures greater than 80F are generally associated with some discomfort.
Values approaching or exceeding 105F are considered life-threatening, with severe heat
exhaustion or heatstroke possible if exposure is prolonged or physical activity high. The
degree of heat stress may vary with age, health, and body characteristics.