So it only took me 5 years of living in the US to realize that the “humidex” reading I grew up hearing on the radio was a Canadian invention and more importantly isn’t used here. Other countries have adopted or adapted it for their own use since Canadian meteorologists came up with it in 1965. The US uses a “heat index” which was developed in 1978 and takes more factors into consideration and uses a lower dew point. Countries with hotter climates love to scoff at our silly reading apparently according to the Ottawa Citizen. At some point there was an attempt to come up with a standard to be used in both countries but the group was disbanded. I think there is some validity to the higher Canadian readings, not that it couldn’t be updated but when you’re used to cooler weather heat causes much more discomfort. I spent the first winter here in NC wearing shorts every single day and spent the summers in front of the A/C vent. Five years later I find myself wearing long sleeves into May’s 20C days and coping with temperatures into the low 90′s with no problem. Maybe what they need is to factor the USDA’s Plant Hardiness Zones and elevation into the equation.
Strangely I still relate cold temperatures in Celsius but hotter temperatures in Fahrenheit. I find myself switching back and forth around 30C/85F (that’s about as hot as it got back home in New Brunswick so I can’t seem to process or relate what a Centigrade temperature over that feels like.)
The calculation used in Canada is Humidex = Temperature + (0.5555 x (vapor pressure – 10)) *vapor pressure in millibars (mb) Or you can use this calculator.