The forecast in London is hot, Hot and HOTTER this week. Summer has arrived on a heat wave that sports our first Humidex advisory. In Canada, a humidex advisory is issued when temperatures reach 30°C or higher. The humidex is really a combination of heat and humidity though, which is a better gauge of comfort levels. As all folks that have lived in Southwestern Ontario can tell you, humidity is the amount of moisture in the air. So a high temperature might be hot, but when you factor in that saturating humidity, the result can be stifling.

Environment Canada doesn’t announce humidex advisories just for fun. When the humidex rating inches higher, your body has a harder time keeping up. All that moisture in the air means that your body can’t properly perspire and regulate its internal temperature. You should increase water intake, reduce physical exertions, and seek cooler conditions when possible. Wear loose-fitting clothes, sunglasses, hats, and sunscreen. The elderly, young children, people with compromised immune systems, and pets are all more vulnerable, so require more attention. If you have spent any time outdoors in the heat of one of our heat waves, you know how miserable they can be. Air like sludge isn’t fun for anyone, and that goes for the fit and feeble anywhere. It’s a wonder that it took until 1965 for Canadians to come up with the humidex scale!

Here is the Humidex Table and Humidex for Relative Humidity Scales from 100% to 65% from the Environment Canada website. As you can see, it doesn’t take much to go from fine to fried.

Humidex Degree of Comfort
20 – 29 No discomfort
30 – 39 Some discomfort
40 – 45 Great discomfort; avoid exertion
46 and over Dangerous; possible heat stroke

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Relative Humidity (%)
Temperature (°C)
100% 95% 90% 85% 80% 75% 70% 65%
21 °C 29 29 28 27 27 26 26 24
22 °C 31 29 29 28 28 27 26 26
23 °C 33 32 32 31 30 29 28 27
24 °C 35 34 33 33 32 31 30 29
25 °C 37 36 35 34 33 33 32 31
26 °C 39 38 37 36 35 34 33 32
27 °C 41 40 39 38 37 36 35 34
28 °C 43 42 41 41 39 38 37 36
29 °C 46 45 44 43 42 41 39 38
30 °C 48 47 46 44 43 42 41 40
31 °C 50 49 48 46 45 44 43 41
32 °C 52 51 50 49 47 46 45 43
33 °C 55 54 52 51 50 48 47 46
34 °C 58 57 55 53 52 51 49 48
35 °C   58 57 56 54 52 51 49
36 °C     58 57 56 54 53 51
37 °C         58 57 55 53
38 °C             57 56

So how do you combat the heat in Southwestern Ontario? It’s time to dine after dark, ditch the oven for the grille, and take up swimming versus sun worshipping. Remember to drink plenty of fluids (water or other salt-replenishing drinks), and think about joining your kids in the sprinkler (on your water days – If your street address ends with a 0, 2, 4, 6 or 8 you may use water outdoors on EVEN numbered calendar days only. If your street address ends with a 1, 3, 5, 7 or 9 you may use water outdoors on ODD numbered calendar days only). If it’s your off day, head to one of London’s many splash pads or pools. Plenty of them are free, while others host days with reduced admission throughout the summer. Most libraries and community centres have air-conditioned facilities as well. Heck, even a trip to the movie theatre is a great way to entertain the family in a cool environment for a couple of hours! It is well worth the gamble of heat stroke, heat exhaustion, or any of the other uncomfortable aspects that come with our summer humidity.

Keep cool this summer Londoners!

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