It’s been a pretty hot summer here, compared to recent ones, and I just got back from a Heritage Day event at Prince’s Island Park (I had some superb tacos, tinga and al pastor, delicious) where it was hotter than it’s been in recent memory, so after I biked home I looked up the temperature. What I found was very interesting: According to a US site, our “heat index” was actually LOWER than our air temperature. But according to a Canadian site, our “humidex,” which most people take to be equivalent to “heat index,” was as one would expect higher than our air temperature.
Humidex and Heat Index might reference the same phenomenon- “apparent temperature”- but they aren’t calculated the same way and don’t report the same result at all. At 2pm, the air temperature in Calgary was 31c (about 88f). The Weather Network, a Canadian TV channel, app and website, reported the “humidex” as 33. The BeWeather app on my phone reported the “feels like” temperature, in the case since BeWeather is a US-based app, the “heat index,” as 29- COOLER than the air temperature since humidity is so low in Calgary. The Canadian “humidex,” which uses dewpoint and not relative humidity in its calculation, from the US perspective, exaggerates the apparent temp. “Heat index” relies on relative humidity, not dewpoint, and underestimates it (from the Canadian perspective).
There has to be a lesson here.