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# Wind Chill Index

This online calculator computes Wind Chill Index using Wind Chill Formula from Environment Canada

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You can read about wind chill in wikipedia but, in short, wind chill, or wind chill index, or wind chill factor, is the felt air temperature on exposed skin due to wind. The wind chill temperature is never higher than the air temperature, and the windchill is undefined at higher temperatures (above 10 °C).

The first wind chill formulae were developed by Paul Allman Siple and Charles Passel working in the Antarctic before the Second World War. Then formulae envolved, and this calculator uses the one from U.S. National Weather Service

$T_{wc}=13.12 + 0.6215 T_a-11.37 V^{+0.16} + 0.3965 T_a V^{+0.16}$
where Twc is wind chill index, in Celsius, Ta is air temperature, V is wind speed in km per hour

Windchill Temperature is only defined for temperatures at or below 10 °C (50 °F) and wind speeds above 4.8 kilometers per hour (about 1.3 meters per second)
This calculator outputs wind chill index for given air temperature and wind speed and also plots the chart for given temperature where wind speed changes from 2 to 35 meters per second. Thus you can see how wind speed effects wind child. For those curious, 35 meters per second is Beaufort number 12 - Hurricane with other values as follows

Wind speed: 1-2 knots (0.3-1.5 m/s) - Beaufort number 1 - Light air
Wind speed: 3-6 knots (1.5-3.3 m/s) - Beaufort number 2 - Light breeze
Wind speed: 7-10 knots (3.3-5.5 m/s) - Beaufort number 3 - Gentle breeze
Wind speed: 11-15 knots (5.5-8.0 m/s) - Beaufort number 4 - Moderate breeze
Wind speed: 16-20 knots (8.0-10.8 m/s) - Beaufort number 5 - Fresh breeze
Wind speed: 21-26 knots (10.8-13.9 m/s) - Beaufort number 6 - Strong breeze
Wind speed: 27-33 knots (13.9-17.2 m/s) - Beaufort number 7 - Near gale
Wind speed: 34-40 knots (17.2-20.7 m/s) - Beaufort number 8 - Fresh gale
Wind speed: 41-47 knots (20.7-24.5 m/s) - Beaufort number 9 - Strong gale
Wind speed: 48-55 knots (24.5-28.4 m/s) - Beaufort number 10 - Storm
Wind speed: 56-63 knots (28.4-32.6 m/s) - Beaufort number 11 - Violent storm
Wind speed: ≥64 knots (≥32.6 m/s) - Beaufort number 12 - Hurricane

### Wind Chill Index

Digits after the decimal point: 1
Wind Chill Index, Celsius

Wind chill dependency on wind speed
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So, why do we need to know wind chill? According to Environment Canada these are the meanings of wind chill index

Wind Chill 0 to -9
Low risk, slight increase in discomfort
Dress warmly, stay dry

Wind Chill -10 to -27
Uncomfortable, risk of hypothermia if outside for long periods without adequate protection.
Dress in layers of warm clothing, with an outer layer that is wind-resistant. Wear a hat, mittens or insulated gloves, a scarf and insulated, waterproof footwear. Stay dry. Keep active

Wind Chill -28 to -39
Exposed skin can freeze in 10 to 30 minutes, Risk of frostnip or frostbite: Check face and extremities for numbness or whiteness. Risk of hypothermia if outside for long periods without adequate clothing or shelter from wind and cold.
Dress in layers of warm clothing, with an outer layer that is wind-resistant. Cover exposed skin. Wear a hat, mittens or insulated gloves, a scarf, neck tube or face mask and insulated, waterproof footwear. Stay dry. Keep active

Wind Chill -40 to -47
Exposed skin can freeze in 5 to 10 minutes. High Risk of frostbite: Check face and extremities for numbness or whiteness. Risk of hypothermia if outside for long periods without adequate clothing or shelter from wind and cold.
Dress in layers of warm clothing, with an outer layer that is wind-resistant. Cover all exposed skin. Wear a hat, mittens or insulated gloves, a scarf, neck tube or face mask and insulated, waterproof footwear. Stay dry. Keep active.

Wind Chill -48 to -54
Exposed skin can freeze in 2 to 5 minutes. Very High Risk of frostbite: Check face and extremities frequently for numbness or whiteness. Serious risk of hypothermia if outside for long periods without adequate clothing or shelter from wind and cold.
Be careful. Dress very warmly in layers of clothing, with an outer layer that is wind-resistant. Cover all exposed skin. Wear a hat, mittens or insulated gloves, a scarf, neck tube or face mask and insulated, waterproof footwear. Be ready to cut short or cancel outdoor activities. Stay dry. Keep active.

Wind Chill -55 and colder
Extremely High risk: exposed skin can freeze in less than 2 minutes. DANGER! Outdoor conditions are hazardous. Stay indoors.