How cold or hot does it really feel outside?
The feels-like temperature: wind chill in the cold, heat index in the heat.
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Feels like
0 °F
Wind chill · Moderate risk: cover up for long stays outside
WC = 35.74 + 0.6215 T − 35.75 V^0.16 + 0.4275 T V^0.16 (T in °F, V in mph)
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The feels-like temperature: wind chill in the cold, heat index in the heat.
How to use
- Type the air temperature and the wind speed from a forecast or a weather station.
- For hot weather, open More options and type the relative humidity; °C, km/h and mph are there too.
- Read how warm or cold it feels, with the frostbite risk or heat danger level.
Wind chill at an air temperature of −10 °C
How it works
Your body loses heat faster in the wind, because moving air keeps carrying away the warm layer next to your skin. Wind chill tells which still-air temperature would cool bare skin as fast. In the heat the problem turns round: humid air slows the evaporation of sweat, so the body cannot cool itself, and the heat index says how hot that feels.
Wind chill uses the 2001 index of the US and Canadian weather services: WC = 35.74 + 0.6215 T − 35.75 V^0.16 + 0.4275 T V^0.16, with T in °F and V the wind in mph at 10 m, as forecasts give it. It applies at 10 °C (50 °F) or colder with wind above 4.8 km/h (3 mph). For example, −10 °C in a 20 km/h wind feels like −18 °C. The heat index is the US National Weather Service's Rothfusz regression of temperature and humidity and applies from about 27 °C (80 °F): 32 °C at 60 % humidity feels like 37 °C.
Outside those ranges the indices are not defined, so the tool shows the air temperature. The heat index is for shade, so direct sun feels hotter, and wind chill never makes objects colder than the air.
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Frequently asked questions
Can wind chill freeze water above 0 °C?
No. Wind makes things cool faster, but never below the air temperature, so water, pipes and car radiators do not freeze above 0 °C.
When is wind chill dangerous?
Environment Canada says exposed skin can freeze in 10 to 30 minutes from a wind chill of −28, and in under 2 minutes at −55 or colder.
Why is there no wind chill in summer?
The index was built for cold weather, at 10 °C or colder. In the heat, humidity matters more than wind, so the heat index is used.
Does humidity affect the wind-chill result?
No. Humidity is used for the heat index, not for the cold-weather wind-chill formula.
Does the result include direct sunshine?
No. The indices assume shade; sunlight, clothing and activity are not modelled.
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