The wind whips up the hair of a pedestrian on a chilly winter day. (Crystal Schick/Yukon News)

Everything you need to know about wind chill

An Environment Canada warning preparedness meteorologist breaks down the winter value

It’s a value that almost all Canadians become intimately familiar with in the winter months: wind chill, the mysterious force that can (allegedly) make -37 C somehow feel even colder than it actually is.

The News spoke to Armel Castellan, Environment Canada warning preparedness meteorologist, to get a better understanding of that other number that’s tacked on to weather forecasts and reports.

What is it?

Wind chill, essentially, is meant to illustrate how much colder the wind blowing makes it feel on your face, the area of your body most likely to be exposed to the elements when you’re outside. It’s calculated with a formula that factors in the true temperature (i.e. the value measured by a thermometer), wind speed, and studies that involved placing volunteers in chilled wind tunnels.

Although expressed in the equivalent of degrees Celsius, when reporting windchill value, Environment Canada doesn’t add a “C” to the end of the number unlike when its reporting actual temperature because windchill can’t actually be measured.

“If you have a room or an outside temperature and it’s -10 C, say, no amount of wind is going to actually change that temperature. The temperature isn’t actually reducing, it’s just that the impact on a sentient being, like a human, is going to be compromised, and therefore the sensation of cold is going to be impacted,” Castellan said. “So we talk about the Celsius … for the actual degree measured by a thermometer, but the windchill is going to be in those same values so that it’s sort of appreciable by the average person, but it’s not going to come with the degree associated with it. So it’s always going to be, it’s -10 C outside, and with a wind of say, 20, 25 kilometres an hour, it’s going to feel like -20.”

In theory, being outside when it’s -10 C with a wind chill of -20 should feel about the same as standing outside when it’s -20 C with no wind, although, Castellan pointed out, it’s rare to ever have conditions where wind is non-existent. Variables like how sunny it is or if exposed skin is dry or wet can also impact how cold someone feels.

A (partly) Canadian invention

Being a country with mid-latitude and northern climates, it’s no surprise that Canadian research has played a significant role in developing the wind chill index as it exists today, Castellan said.

According to the Environment Canada website, the agency hosted the “first global internet workshop” on wind chill in 2000 that saw more than 400 participants from 35 countries attend. Almost all participants agreed that there needed to be an international standard for reporting wind chill, the website says, and, in 2001, a team of Canadian and American scientists and medical experts worked together to create the wind chill index as we know it today.

Volunteers from the Department of National Defence also lent their faces to the cause, Castellan said.

“(We exposed) them to different conditions and had them wear different types of clothing (and) put them in a refrigerated wind tunnel,” he said. “Some of them were dressed in proper winter clothing, others had different levels of activity within that wind tunnel … so, you know, someone walking on treadmills and others had wet clothing, wet faces, to simulate kind of a real-world example where if you’re caught in a blizzard, you are going to have snow being kicked up and it’s going to melt on your body so you are going to have that melted component or moisture, so those are pretty important parts of establishing how cold that wind chill should be for a given temperature and wind strength.”

Public surveys done by Environment Canada show that 82 per cent of Canadians now use the wind chill value when planning on how to dress for going outside, Castellan said. It’s also become a valuable tool for schools, public health agencies and sports clubs to determine when to cancel outdoor activities. In general, it’s recommended to cover as much skin as possible before going outside in the cold, especially when the wind chill drops below -27 — that’s when the risk of frostbite increases significantly.

A different impact on everyone

Much like the humidex, which happens to be another Canadian invention, wind chill’s impact on any particular person will vary based on someone’s age, weight, body size and body shape.

“A tall, slim person is going to be impacted by the cold much quicker than a shorter, stockier or sturdier person because they have more exposure for their muscle mass, and that’s also true for elderly and children because they don’t have as much muscle, so their metabolism can’t generate as much heat per kilogram of body mass,” Castellan said.

Contact Jackie Hong at jackie.hong@yukon-news.com

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