**** Info via Environment Canada
Humidex: the “unbearable heat” index
It’s not the heat, as they say, it’s the humidity. In fact, humidity changes our perception of how hot or cold it is. The higher the mercury rises, the more moisture in the air and the hotter it can feel. The humidex measures the combined effects of heat and humidity regarding our comfort (or discomfort). A humidex number of over 40 is considered extremely high, with serious risks of heat stroke and sunstroke.
The humidex is a Canadian innovation that was first used in 1965. It describes how hot, humid weather feels to the average person. The humidex combines the temperature and humidity into one number to reflect the perceived temperature. Because it takes into account the two most important factors that affect summer comfort, it can be a better measure of how stifling the air feels than either temperature or humidity alone.
While the humidex is widely used in Canada, extremely high readings are more common in the southern regions of the Prairies, Ontario, and Quebec. The humidex usually decreases as latitude increases. Of all Canadian cities, Carman, Manitoba, holds the highest recorded Humidex level at 53 on July 25, 2007.
A guide to summer comfort
An extremely high humidex is any reading over 40. In such conditions, you should reduce all unnecessary physical activity. If the reading is in the mid to high 30s, you should tone down or modify certain types of outdoor exercise, depending on the individual age and health, physical shape, clothes worn, and other weather conditions.
If working outdoors is absolutely necessary, drink plenty of liquids and take frequent rest breaks. There is a considerable risk of heat stroke and sunstroke in hot, humid conditions.
To learn more: How to protect yourself from the health effects of extreme heat.
