Humidex

The humidex (short for humidity index) is an index number used by Canadian meteorologists to describe how hot the weather feels to the average person, by combining the effect of heat and humidity.

[1] The humidex is a nominally dimensionless quantity (though generally recognized by the public as equivalent to the degree Celsius) based on the dew point.

Range of humidex: Scale of comfort:[2][3] The current formula for determining the humidex was developed by J. M. Masterton and F. A. Richardson of Canada's Atmospheric Environment Service in 1979.

Humidex differs from the heat index used in the United States in being derived from the dew point rather than the relative humidity, though both dew point and relative humidity (when used in conjunction with air temperature) are directly related to atmospheric moisture.

The humidex is higher than the U.S. heat index at equal temperature and relative humidity.

The 1979 reformulation, which added the 0.5555 factor (from the relation 1 °F = ⁠5/9⁠ °C), was largely to address metrication in Canada as the country switched to the Celsius scale.