Glossary

Wednesday, 8 Oct 2008

Wind Chill

Wind chill is the cooling our body feels when the impact of temperature and wind are combined. Normally, on a relatively calm day our body is able to provide some protection from the outside temperature by heating up a thin layer of air that lies close to the skin. This added insulation is known as a boundary layer. On windy days, however, this insulating layer gets taken away, leaving our skin more exposed to the outside temperature. It takes time and energy for our body to warm up another layer of air, and if this layer continually gets blown away, eventually our skin's temperature will fall and our body will feel colder.

The wind can also make our body feel colder through the evaporation of any existing moisture from our skin. Through this process more heat is drawn from our body.

The Evolution of the Wind Chill Index

The first wind chill formula was based on experiments conducted in 1939 by two Antarctic explorers. Over time this formula was modified, but stayed based on the original experiments. In the year 2000, Canada decided to head a committee to develop a New Wind Chill formula. Spear headed by the Environment Canada branch of the federal government, more than 35 countries participated. It was agreed by all parties involved that the new formula and reporting methods for wind chill would be more accurate, easier to understand, and incorporate new scientific knowledge.

The new wind chill index is based on the loss of heat from the face only - the area of the body that is most exposed to severe winter weather conditions. After conducting some additional research it was decided that wind chill readings would be expressed in temperature like units so that it would be easier to comprehend. The new wind chill index has been adopted by the United States as well ensuring that information will be consistent throughout the majority of North America.

Wind Chill Range	Rating	Impact
0 to -9	Low	Minor increase in discomfort
-10 to -24	Moderate	Uncomfortable Bared skin feels cold Danger of hypothermia if outdoors for extended periods
-25 to -44	Cold	Danger of skin freezing (frostbite) Remember that the average person's skin begins to freeze at a wind chill of -25 Examine face, fingers, toes, ears and nose for numbness or whiteness Threat of hypothermia if outdoors for extended periods
-45 to -59	Extreme	Exposed skin may freeze in mere minutes Examine face, fingers, toes, ears and nose for numbness or whiteness Severe danger of hypothermia if outdoors for long periods Be prepared to end outdoor activities early or cancel them completely
-60 or colder	DANGER! HIGH RISK!	Conditions outside are hazardous Skin left uncovered may freeze in under 2 minutes If possible stay indoors

To learn more about wind chill, please click on the links below: