Wind Chill and Frostbite Time Calculator
An aurora night usually means standing still in the cold for hours, often on open ground or by the sea where the wind has nothing to stop it. Type the temperature and wind from your forecast below. You get the wind chill, how soon bare skin can freeze, and Environment Canada's advice for that level, so you know what has to be covered before you go out.
Wind chill and frostbite time
Type in the temperature and wind from your forecast. You get the wind chill, how soon exposed skin can freeze, and Environment Canada's advice for that level.
- Exposed skin can freeze in
- Wind on your face
- In the other units
Wind chill around your numbers
What wind chill is
Environment and Climate Change Canada explains it simply. On a still day your body keeps a thin layer of warm air next to your skin. Wind blows that layer away and dries your skin, so you lose heat faster and feel colder. Wet skin cools quicker still. The wind chill is a "feels like" temperature for that. If the air is -10°C and the wind chill is -20, your skin in the wind feels as it would at -20°C on a calm day.
It does not make things colder than the air. ECCC and the US National Weather Service both make the point: a car or a water pipe only cools to the air temperature, just faster. Wind chill is about people and animals. The NWS adds that you can only get frostbite if the air itself is below freezing, however low the wind chill reads. Above freezing, you can still become hypothermic.
The formula
Canada and the United States have used the same index since 2001. The NWS gives it in Fahrenheit: wind chill = 35.74 + 0.6215T − 35.75V0.16 + 0.4275TV0.16, with T the air temperature in °F and V the wind in mph. Environment Canada's Celsius form is 13.12 + 0.6215T − 11.37V0.16 + 0.3965TV0.16, with V in km/h. The calculator uses the one that matches the units you pick. Our test runs every cell of ECCC's published chart through it. 65 of the 66 cells match exactly. The 66th, -30°C at 30 km/h, works out at -45.6, which ECCC prints as -45.
The NWS says the index:
- takes the wind from the standard 33 ft (10 m) anemometer height of a forecast and works it down to 5 ft, the height of an adult face;
- is based on a model of the human face and on heat lost from the body on cold, windy days;
- assumes no sun, a clear night sky, which is exactly an aurora night. In bright sunshine, the NWS says, the wind chill can be 10°F to 18°F warmer;
- leaves humidity out, because in tests on 12 people it changed the result by less than a degree.
The NWS defines it only at or below 50°F (10°C) and for wind above 3 mph (5 km/h). Outside those limits, the calculator shows the air temperature. ECCC only puts wind chill in its forecasts at 0°C or colder with wind of 5 km/h or more.
The risk bands and how fast skin freezes
These are Environment Canada's bands, word for word. The calculator colours its answer and chart by them.
| Wind chill | Risk | What ECCC says |
|---|---|---|
| 0 to -9 | Low | Slight increase in physical discomfort. |
| -10 to -27 | Moderate | Physical discomfort; risk of hypothermia and frostbite if outdoors for long periods of time without adequate protection. |
| -28 to -39 | High | 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. |
| -40 to -47 | Very high | Any exposed skin can freeze in 5 to 10 minutes. Very high risk of frostbite and of hypothermia. |
| -48 to -54 | Severe | Exposed skin can freeze in 2 to 5 minutes. Check your face and extremities frequently for numbness or whiteness. Severe risk of hypothermia. |
| -55 or colder | Extreme | Exposed skin can freeze in less than 2 minutes. DANGER! Outdoor conditions are hazardous. |
ECCC adds a footnote: in sustained winds over 50 km/h (31 mph), frostbite can happen faster than the band says. It also says the frostbite risk is the same at -28°C with no wind as at a wind chill of -28. The difference is that frostbite comes faster with the wind. The bands are in Celsius. If you work in Fahrenheit, the calculator converts for you. The NWS notes that the index was tested on adults, so be even more careful with children, older people and anyone in poor health.
The signs to watch for, and what to do about them, are in frostbite and hypothermia signs to know.
Moving makes it colder
Wind chill is about the air moving past your face, and it makes no difference whether the air moves or you do. On a snowmobile safari, a dog sled or skis, your own speed adds to the wind when you head into it. The calculator adds the speed you type to the forecast wind. That is our own step, not part of either weather service's index, and it is the worst case: with the wind behind you, it would partly cancel. Your own speed is at face height already, so adding it to a wind measured 10 m up overstates things a little. Take the answer as a ceiling.
Aurora nights, worked through
The calculator's own output for some typical nights:
| Air | Wind | Your speed | Wind chill | Risk | Exposed skin can freeze in |
|---|---|---|---|---|---|
| -15°C (5°F) | 10 km/h | standing | -21 (-6°F) | Moderate | not within 30 min |
| -15°C (5°F) | 10 km/h | 30 km/h snowmobile | -27 (-17°F) | Moderate | not within 30 min |
| -25°C (-13°F) | 5 km/h | standing | -30 (-22°F) | High | 10 to 30 min |
| -25°C (-13°F) | 15 km/h | standing | -35 (-31°F) | High | 10 to 30 min |
| -30°C (-22°F) | 5 km/h | 40 km/h snowmobile | -48 (-55°F) | Severe | 2 to 5 min |
| -35°C (-31°F) | 10 km/h | standing | -45 (-49°F) | Very high | 5 to 10 min |
| -40°C (-40°F) | 20 km/h | standing | -56 (-68°F) | Extreme | under 2 min |
Look at the fifth row. A still -30°C night is high risk standing by the cabin, but on the snowmobile ride out to the viewing spot it becomes severe, with bare skin freezing in minutes. Cover your face before you set off, not when you arrive. Even a light breeze makes a big difference at the cold end: -25°C goes from -30 to -35 between 5 and 15 km/h.
How cold it gets during the northern lights gives the temperatures to expect at the main destinations. For what to wear, see merino or synthetic base layers, gloves you can work a camera in, hand warmers and heated jackets. You can also rent the heavy kit when you arrive. For when things go wrong, gear to survive an Arctic night emergency covers it. To pick the night itself, the aurora visibility tool gives the Kp you need and the dark hours.
General information from the weather services, not medical advice. Frostbite and hypothermia need medical care; in an emergency, call your local emergency number.
Sources: Environment and Climate Change Canada, Wind chill and the Wind Chill Index (page dated 16 December 2025); US National Weather Service, Wind Chill Chart and FAQ.