Humidex Information
The humidex is an index used by Canadian meteorologists to describe how hot the weather feels to the average person, by combining the effect of heat and humidity. For example, if the temperature is 30° C and the calculated humidex is 40, that indicates that the humid heat feels approximately like a dry temperature of 40°. The index is widely used in Canadian weather reports during summer.
According to the Meteorological Service of Canada, a humidex of at least 30 causes "some discomfort", at least 40 causes "great discomfort" and above 45 is "dangerous." When the humidex hits 54, heat stroke is imminent.
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 dew point rather than relative humidity.
The record humidex in Canada occurred on July 25, 2007, when Carman, Manitoba hit 53.0.[1] This breaks the previous record of 52.1 set in 1953 in Windsor, Ontario (The residents of Windsor would not have known this at the time, since the humidex had yet to be invented).
Contents |
Humidex formula
When the temperature is 30 °C (86 °F) and the dew point is 15 °C (59 °F), the humidex is 34 (note that humidex is a dimensionless number, but that the number indicates an approximate temperature in °C). If the temperature remains 30 °C and the dew point rises to 25 °C (77 °F), the humidex rises to 42. The humidex tends to be higher than the U.S. heat index at equal temperature and relative humidity.
The humidex formula is as follows:
- humidex = (air temperature in Celsius) + h
- h = (0.5555)*(e - 10.0)
- e = 6.11 * exp [5417.7530 * ((1/273.16) - (1/dewpoint in kelvins))]
Complete:
See also
References
External links
- "Frequently Asked Questions", MSC, 2004.
- Wind Chill and Humidex Criticism about the use of Wind chill and humidex
- More Humidex info
Categories: Atmospheric thermodynamics | 1979 establishments | Climate of Canada
|