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Wind Chill Temperature Measurement

Quick Tips #295 

On blustery winter days, it's not uncommon to see two temperature readings given on your local weather report. That's because the air temperature taken alone doesn't always tell the whole story. Some seemingly moderate days will feel much colder, simply because the wind is blowing. This effect is known as the wind chill factor. The wind chill index is a method that compensates for the wind chill factor using wind speed to calculate a measurement called the wind chill temperature (WCT). The wind chill temperature measurement is a more realistic number in terms of how the cold feels to human skin. This is essential information for anyone gearing up to work or play outdoors. For additional safety, the method also includes a frostbite danger index.

The wind chill index used in the U.S. and Canada was developed using the latest advances in science, computer modeling and technology. The index is based on:

  • Wind speed measured at average face height of 5 feet off the ground, where the face is the most likely part of the body to be exposed to the wind
  • A consistent standard for skin tissue resistance
  • Heat transfer theory (heat loss from the body to surroundings during cold windy periods)
  • A calm wind threshold of 3 mph
  • A standard consistent with skin tissue resistance
  • Assumes no heat impact from the sun (clear night sky conditions)

Referring to the chart below, we see that a temperature of 10°F with a wind speed of 20 mph, results in a wind chill temperature of -9°F. This variation could make a big difference in the type of clothing you'd choose to wear when spending time outdoors.

 

Wind Chill Chart

If you know the air temperature and wind speed, the wind chill temperature and frostbite risk can easily be determined using this reference chart. The information is also incorporated into the latest software available on the National Weather Service's Advanced Weather Interactive Prediction System.

Commonly Asked Questions

Q.   What is the wind chill temperature?
A.   Wind chill temperature is the temperature it feels like outside to people and animals. Wind chill is based on the rate of heat loss from exposed skin caused by combined effects of wind and cold.
 
Q.   What is frostbite?
A.   Frostbite is the result of the body tissue freezing and most frequently affects the extremities such as fingers, nose and toes. Symptoms include a pale white appearance and loss of feeling in these extremities.
 
Q.   What is an anemometer?
A.   An anemometer is a device for measuring wind speed.
 
Q.   What is hypothermia?
A.   Hypothermia occurs when the body temperature falls below 95°F. Hypothermia is caused by exposure to cold and is aggravated by wet, wind and exhaustion. Warning signs include uncontrollable shivering, disorientation, memory loss, slurred speech, incoherence, drowsiness and exhaustion.

 

Source

NOAA-National Oceanic and Atmospheric Administration

(Rev. 1/2012)

 

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at www.grainger.com/quicktips.

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Please Note:
The content in this newsletter is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific compliance questions should refer to the cited regulation or consult with an attorney.

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