![]() "Within half a minute, it was up to 45 degrees." "It rose to 37 degrees within a minute," he says." To illustrate how variable even temperature can be, David Phillips conducted his own little experiment.įirst, he took a reading the standard way: in the shade. ![]() The winter equivalent to the humidex is wind chill - an index ironically invented by Americans instead of by someone north of the 49th parallel. In the past century, there have been numerous attempts in North America to try to calculate how uncomfortable people feel in the sticky heat.Īmong them are the discomfort index, humiture index and even the aptly named humisery index. Above 45 is considered dangerous since it brings the possibility of heatstroke. That rises to "great discomfort" from 40 to 45, when residents are told to avoid exertion. When the humidex reaches 30 to 39, Canada's weather agency suggests those outside may feel "some discomfort." But it really is kind of an imperfect index by science's standards, and it is one of several ways of trying to sound the misery alarm about summertime heat. Providing the public with a way to assess the danger of the sweltering outdoors is the reason for the development of the humidex in the first place. The humidex "gives you a measure of how effectively your body can cool down," "The issue really is a health issue," says Peter Taylor, a professor of atmospheric science at Toronto's York University. That's when a person's body temperature rises and they can suffer a slew of heat-related problems, from a minor heat rash to a potentially deadly heatstroke. In summer, sweat helps cool you down.īut when the humidity is high and the air is already nearly saturated with moisture, sweat evaporation stops. "The way it air conditions is when we perspire, that moisture in our skin evaporates into the air and that takes away some of the heat from our body."īodies try to maintain a temperature of 37 C. The index is based on a calculation of heat and humidity by using current air temperature and the dew point (the temperature and barometric pressure at which water vapour condenses into liquid). It matters because humidity can wreak havoc on a body's internal cooling systems. If the forecast cites a humidex of 40, for example, it means that the temperature might be 35 C but, with the humidity, the discomfort feels like it would at a dry temperature of 40 C. The humidex - short for humidity index - is a Canadian innovation first used in 1965, according to Environment Canada. ![]() Carman, a rural farming town in southern Manitoba, hit a humidex level of 53 on July 25, 2007. "That has been surpassed by an unlikely place," said Phillips. It held the record of a humidex of 52.1 from Jfor more than half a century. So there's not nearly as much tossing and turning."įor years, the southern Ontario city of Windsor earned the reputation as the humidex capital of Canada. ![]() Those calls are because the typically dry Prairie provinces are experiencing higher humidity levels due to increased air flows from the south these days, and these are adding to the high moisture levels caused by the "feverishly" growing crops, says Phillips.īut he also notes that, for most Westerners, the higher humidity "is not nearly as debilitating because they cool down at night. "I get more calls in Saskatchewan and Manitoba now: 'What is this thing called humidex? Is it something that Toronto manufactured?'" says David Phillips, Environment Canada's senior climatologist. The term - a Canadian innovation - is one used most often by southern Ontarians and Quebecers, though Canada's weather guru says that's changing. If you're not quite sure what the humidex is, you're not alone.
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