Wind chill in Canada: how it's calculated
Canada uses the North American wind chill index to express how cold the air feels on exposed skin. Here is the formula, the science, and the frostbite risk it flags.
Wind chill is a number that expresses how cold the air actually feels on exposed skin once wind is factored in, because moving air strips away the thin layer of warmth your body maintains. Canada uses the North American wind chill index, adopted by Environment and Climate Change Canada in 2001, which combines air temperature and wind speed into a single temperature-like figure. It is reported in degrees but is technically dimensionless — a wind chill of -30 means the cooling effect on your skin is equivalent to a calm -30 °C.
How is wind chill calculated in Canada?
The Canadian wind chill index is derived from a formula developed jointly by scientists in Canada and the United States and validated with human trials at Defence Research and Development Canada in Toronto, where volunteers had temperature sensors on their faces while walking in a refrigerated wind tunnel. The equation is:
W = 13.12 + 0.6215 T − 11.37 V0.16 + 0.3965 T V0.16
Here W is the wind chill index, T is the air temperature in degrees Celsius, and V is the wind speed in kilometres per hour measured at the standard 10-metre anemometer height. The result is rounded to the nearest whole number. Because it is based on real physiology rather than the old 1940s "watts per square metre" heat-loss model, the modern index gives a far more realistic sense of frostbite risk.
Why does wind make it feel colder?
Your body constantly warms a razor-thin boundary layer of air against your skin. On a calm day that layer acts as insulation. Wind blows it away as fast as you can rebuild it, so heat drains from your skin much faster — the stronger the wind, the faster the loss. Crucially, wind chill only describes how quickly exposed skin loses heat; it cannot make anything colder than the actual air temperature. Water in a puddle will not freeze faster because of wind chill, and a car engine will not cool below the true air temperature. The index is about living tissue, which is why it is expressed in terms of frostbite risk.
What wind chill is dangerous?
ECCC pairs each wind chill range with a frostbite risk so the number means something practical.
| Wind chill | Risk to exposed skin |
|---|---|
| 0 to −9 | Uncomfortable; low risk. |
| −10 to −27 | Increasing discomfort; risk of frostbite with prolonged exposure. Dress warmly. |
| −28 to −39 | Exposed skin can freeze in 10 to 30 minutes. Cover up. |
| −40 to −47 | Exposed skin can freeze in 5 to 10 minutes. Check for numbness. |
| −48 to −54 | Skin can freeze in 2 to 5 minutes. Outdoor conditions hazardous. |
| −55 and colder | Skin can freeze in under 2 minutes. Stay indoors. |
ECCC issues an extreme cold warning when the temperature or wind chill is expected to reach a regional threshold — commonly around −40 to −50 in much of the country — because that is when the danger of frostbite and hypothermia becomes acute for anyone caught outside.
Is wind chill the same as the "feels like" temperature?
Not quite. Wind chill only applies in cold conditions, generally when the air temperature is at or below 10 °C and the wind is above about 5 km/h. In warm weather Canada uses a separate index, the Humidex, which combines temperature and humidity to describe how hot it feels. A phone app's single "feels like" figure typically switches between wind chill in winter and Humidex in summer under the bonnet. The two indices are computed differently and are never used at the same time.
What are the limits of the wind chill index?
The formula assumes an adult walking at roughly 5 km/h into the wind, with a bare, dry face at night (to remove any warming from sunshine). It does not account for sunshine, which can make you feel several degrees warmer, nor for wet skin, which loses heat far faster, nor for individual factors such as age, fitness, or clothing. It also uses the wind speed at 10 metres, so gusts at street level or in exposed spots may bite harder than the reported figure suggests. Treat the number as a well-calibrated guide, not a precise measurement of your personal experience.
How reliable is a forecast wind chill?
A forecast wind chill is only as good as the two forecasts feeding it — temperature and wind — and wind speed in particular is one of the harder variables to nail down, especially in complex terrain or near coastlines. Forecast models such as ECCC's GEM, the ECMWF, and the GFS can disagree on how strong the wind will be, which shifts the wind chill by several degrees. At checkweather.io we compare those models directly and express their agreement as a forecast-confidence score, then track how the predicted wind chill held up against observations on our accuracy scoreboard, so you know whether tomorrow's dramatic-looking number is well supported or a single model's outlier.
The bottom line
Wind chill turns two numbers — air temperature and wind speed — into one that tells you how fast your skin will lose heat and how quickly it could freeze. It cannot cool objects below the true air temperature and it does not apply in warm weather, where Humidex takes over. When ECCC posts a wind chill of −35 or an extreme cold warning, treat it as a countdown clock for exposed skin and dress accordingly.