Wind chill and the Wind Chill Index
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- Estimate the wind chill with our calculator
- About extreme cold events and cold warnings
About wind chill
The weather outside feels colder when it is windy, and we call this the wind chill. We use wind chill in our forecast to show how cold it will feel outside to help you make decisions to stay safe from cold weather.
How wind affects your body in cold weather
On cold days with no wind, your body makes a thin layer of warm air around your skin. When the wind blows, this thin layer blows away, dries the moisture off your skin, and makes you feel colder.
When this layer evaporates, you lose heat faster and your body has to work harder to warm up a new layer of air.
If your skin is wet, it gets cold even quicker as there is more moisture to evaporate.
Strong winds make it easier to get cold injuries like frostbite and hypothermia. If the air temperature is -28°C with no wind, or if the wind chill is -28, the risk of frostbite is the same, but frostbite will occur faster with wind.
How we measure wind chill
Wind chill cannot be measured with a thermometer. It is felt by our skin. Since air temperature is measured in degrees (°) Celsius, we use it to help people understand how cold it feels in the wind.
For example, if the outside temperature is -10ºC, but the wind chill is -20, when you are in the wind it will feel like -20 degrees Celsius on your skin.
How wind chill relates to temperature
Wind chill affects how fast the body and objects lose heat, making it feel colder than the actual temperature. However, wind chill doesn’t make things colder than the real air temperature.
For example, if the air temperature is -20°C and the wind chill is -30, objects outside will only cool to -20°C, not -30°C.
The Wind Chill Index
The wind chill index is how we calculate the feeling of cold from the wind, when temperatures are below zero. We use the wind chill index to help describe the risk of frostbite. This helps show how the cold really feels, so that you can take action to stay safe.
When the temperature is above zero, we don't show the wind chill because there is no risk of frostbite no matter how windy it is. Even so, you can still feel colder due to wind chill.
How we forecast wind chill
When temperatures are zero or below and the wind speed is 5 km/h or higher, we include wind chill in the weather conditions and forecasts. We only send out wind chill forecasts for today, tonight and tomorrow. We do not include wind chill for the full seven-day weather forecast.
If there is a big difference in the morning and afternoon wind chill, we send two wind chill forecasts for the day. If the wind chill is cold enough, we will also include frostbite information in the forecast.
Your safety risk for wind chill exposure
Find out the safety risk with different wind chill values.
Low risk exposure
- 0 to -9 wind chill value
- slight increase in physical discomfort
Moderate risk exposure
- -10 to -27 wind chill value
- physical discomfort
- risk of hypothermia and frostbite if outdoors for long periods of time without adequate protection
High risk exposure
- -28 to -39 wind chill value
- any exposed skin can freeze in 10 to 30 minutes
- high risk of frostnip or frostbite: check your face and extremities for numbness or whiteness
- high risk of hypothermia if you remain outside for long periods without adequate clothing or shelter from wind and cold
Very high risk exposure
- -40 to -47 wind chill value
- any exposed skin can freeze in 5 to 10 minutesFootnote 1
- very high risk of frostbite: check your face and extremities for numbness or whiteness
- very high risk of hypothermia if you are outside for long periods without adequate clothing or shelter from wind and cold
Severe risk exposure
- -48 to -54 wind chill value
- exposed skin can freeze in 2 to 5 minutesFootnote 1
- severe risk of frostbite: check your face and extremities frequently for numbness or whiteness. There is severe risk of hypothermia if you are outside for long periods without adequate clothing or shelter from wind and cold
Extreme risk exposure
- -55 or colder wind chill value
- exposed skin can freeze in less than 2 minutesFootnote 1
- DANGER! outdoor conditions are hazardous
How to estimate the wind chill
The chart below helps you estimate wind chill with wind speed plus the temperature outside. You can estimate wind speed by watching the movement of trees and flags.
You can also use our wind chill calculator to estimate your own wind chill values:
| Wind speed (km/h) | Estimating wind speed - what to look for | 0 | - 5 | -10 | -15 | -20 | -25 | -30 | -35 | -40 | -45 | -50 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10 | Wind felt on face - wind vane begins to move | -3 | - 9 | -15 | -21 | -27 | -33 | -39 | -45 | -51 | -57 | -63 |
| 20 | Small flags extended | -5 | -12 | -18 | -24 | -30 | -37 | -43 | -49 | -56 | -62 | -68 |
| 30 | Wind raises loose paper, large flags flap and small tree branches move | -6 | -13 | -20 | -26 | -33 | -39 | -45 | -52 | -59 | -65 | -72 |
| 40 | Small trees begin to sway and large flags extend and flap strongly | -7 | -14 | -21 | -27 | -34 | -41 | -48 | -54 | -61 | -68 | -74 |
| 50 | Large branches of trees move, telephone wires whistle | -8 | -15 | -22 | -29 | -35 | -42 | -49 | -56 | -63 | -69 | -76 |
| 60 | Trees bend and walking against the wind is hard | -9 | -16 | -23 | -30 | -36 | -43 | -50 | -57 | -64 | -71 | -78 |
How we calculate wind chill
We calculate wind speed and temperature together to give a “feels like temperature” for wind chill. We cannot measure wind chill with a thermometer. For example, see how we would calculate wind chill below:
| Temperature | Wind Speed | Resulting Wind Chill |
|---|---|---|
| -15ºC | 20 km/h | -24 |
| -20ºC | 30 km/h | -33 |
| -30ºC | 40 km/h | -48 |
Try the Wind chill calculator to estimate your own wind chill values.