How does wind chill work?

We need to talk about wind chill and get one thing straight: Temperature and wind chill are not the same thing!

They are not interchangeable. I can’t tell you the number of times I have heard that it was -40 C this morning or that it is going to get down to -40 C this weekend. It has never been -40 C in Toronto.

The coldest temperature that has ever been recorded at the Toronto Pearson Airport is -31.3 C on January 4, 1981. On that day, we also saw our lowest wind chill value of -45 and that was only for one hour.

One of the other common mistakes I notice floating around on social media is the usage of the degree symbol when someone is talking about the wind chill.

Wind chill is a calculated value and does not have the same units of measurement as the temperatures scale. Therefore, when stating what the wind chill is, it is merely the numerical value without a symbol.

How does wind chill work?

Wind chill is a calculation that combines air temperatures, the wind speed and how these together will affect your body’s ability to keep warm.

We use wind chill as a tool to gauge health risks on people and pets, instead of it being a true observed measurement.

Wind chill doesn’t impact buildings or your car’s battery, but it does impact you and your family.

On a calmer day, the heat produced by your body will create a small bubble of warm air around you that acts as a barrier between the cold air and your skin. When it is windy that layer is blown away from your body and you feel accelerated effects from the cold on your body’s temperature.

If you are wet or wearing wet clothing or shoes, you will be even colder, even faster. Your body then has to spend more energy to try and warm yourself and the core body temperatures can start to drop.

Stronger wind passing over exposed skin can cause cold-related health issues to settle in faster. This mainly is an issue for exposed skin on humans, but pets too can feel the effects. So make sure you are taking precautions to ensure that the heat is not escaping off of them too.

Wind chill risks

Frost Bite

Frost bite can occur in a matter of minutes on some of the most extreme wind chill days that we see here in Toronto. This is basically when your skin and the tissue below it freeze, and can be permanently damaged. Your ears, nose, fingers and toes are the most likely spots to get frost bite.

See the chart below for how quickly unprotected skin can freeze:

Hypothermia

There are a few signs of hypothermia and it is something that can be incredibly dangerous if you don’t seek medical attention quickly enough. Your body can shut down after working too hard to keep your core temperature up.

The chart below shows some of the signs for hypothermia:

The stats

The coldest wind chill ever recorded in Canada is -78 in Kugaaruk, Nunavut on January 13, 1975. The air temperature at the time was -51 Degrees and the winds were howling at 56 km/h.

In Toronto, we will average roughly 23 days each year where we hit wind chill values below -20. Of those 23 days, three will be below -30 and almost one of them hit will hit -40. There are only three months out of the year that there hasn’t ever been a wind chill value reported. Those are obviously June, July and August.

Wind chill extremes by month

Sep: -8

Oct: -14

Nov: -25

Dec: -38

Jan: -45

Feb: -39

Mar: -36

Apr: -25

May: -10

Cold weather alert

The city of Toronto’s extreme cold weather alert program uses the wind chill calculation to decide on when they are going to open warming centres in the city.

They will issue an extreme cold weather alert when wind chill values are expected to reach or exceed -20 or the air temperatures is expected to hit -15°.