Wind Chill Program

Wind Chill Fact Sheet

Wind Chill Hazards and Thresholds
Cold Injuries
Factoids and Quiz

Canada's new wind chill index!

Canada now has a new wind chill index! The new index is more accurate, easy to understand and reflects the needs of Canadians. It is based on new research, using human volunteers and advanced computer technology, combined with recent medical advances in the understanding of how the body loses heat when exposed to cold. As a result, the wind chill forecasts you hear will now be much closer to what you actually feel.

The new index is expressed in temperature-like units, the format preferred by most Canadians. The index likens the way your skin feels to the temperature on a calm day. For example, if the outside temperature is -10°C and the wind chill is -20, it means that your face will feel as cold as it would on a calm day when the temperature is -20°C.

The new wind chill index enables Canadians to take action to avoid injuries from the cold, such as dressing warmly to avoid frostbite, and to make good decisions based on accurate information, such as whether school children should be let outdoors for recess.

On cold and blustery winter days, listen for the new wind chill index in your local weather forecast!

What is Wind Chill?

Anyone who has ever waited at a bus stop or taken a walk on a blustery winter day knows that you feel colder when the wind blows. We call the cooling sensation caused by the combined effect of temperature and wind the wind chill.

On a calm day, our bodies insulate us somewhat from the outside temperature by warming up a thin layer of air close to our skin, known as the boundary layer. When the wind blows, it takes this protective layer away-exposing our skin to the outside air. It takes energy for our bodies to warm up a new layer, and if each one keeps getting blown away, our skin temperature will drop, and we will feel colder.

Wind also makes you feel colder by evaporating any moisture on your skin-a process that draws more heat away from your body. Studies show that when your skin is wet, it loses heat much faster than when it is dry.

How Wind Chill Affects You

Living in a cold country can be hazardous to your health. Each year, in Canada, more than 80 people die from over-exposure to the cold, and many more suffer injuries from hypothermia and frostbite. Wind chill can play a major role in such health hazards because it speeds up the rate at which your body loses heat.

How much heat you lose depends not only on the wind chill, but on other factors as well. Good quality clothing with high insulating properties traps air, creating a thicker boundary layer around the body which keeps in the heat. Wet clothing or footwear loses its insulated value, resulting in body-heat loss nearly equal to that of exposed skin. Your body type also determines how quickly you lose heat-- people with a tall slim build become cold much faster than those that are shorter and heavier.

In addition, we can also gain heat by increasing our metabolism or soaking up the sun. Physical activity, such as walking or skiing, increases our metabolism and generates more body heat. Age and physical condition also play a part: elderly people and children have less muscle mass, so they generate less body heat. Sunshine, even on a cold winter day, can also make a difference. Bright sunshine can make you feel as much as ten degrees warmer.

Over time, our bodies can also adapt to the cold. People who live in a cold climate are often able to withstand cold better than those from warmer climes.

Beating the Chill

The best way to avoid the hazards of wind chill is to check the weather forecast before going outside, and be prepared by dressing warmly. As a guideline, keep in mind that the average person's skin begins to freeze at a wind chill of -25, and freezes in minutes at -35.

A simple way to avoid wind chill is to get out of the wind. Environment Canada's wind chill forecasts are based on the wind you would experience on open ground. Taking shelter from the wind can reduce or even eliminate the wind chill factor. However, you would still feel cold from the outside temperature alone.

A recent survey indicated that 82 per cent of Canadians use wind chill information to decide how to dress before going outside in the winter. Many groups and organizations also use the system to regulate their outdoor activities. Schools use wind chill information to decide whether it is safe for children to go outdoors at recess. Hockey clubs cancel outdoor practices when the wind chill is too cold. People who work outside for a living, such as construction workers and ski-lift operators, are required to take indoor breaks to warm up when the wind chill is very cold.

Towards a Better Wind Chill

Wind chill describes a sensation, the way we feel as a result of the combined cooling effect of temperature and wind. This feeling can't be measured using an instrument, so scientists have developed a mathematical formula that relates air temperature and wind speed to the cooling sensation we feel on our skin.

The original wind chill formula was derived from experiments conducted in 1939 by Antarctic explorers, Paul Siple and Charles Passel. These hardy scientists measured how long it took for water to freeze in a small plastic cylinder when it was placed outside in the wind. Over the years, the formula was modified somewhat, but remained based on the Antarctic experiments.

The original formula was useful, but there was a need for improvement. There is a considerable difference between a human body and a plastic cylinder filled with water, most notably the fact that people produce body heat. As well, the wind speed used in the formula is measured ten metres above the ground, usually at airport weather stations. At this height, the winds are faster than those at 1.5 metres, the height of an average person. As a result, the method produced a colder wind chill than people actually experienced.

New Science and a New Standard

Canada took the lead in an international effort to develop a new wind chill formula. In April 2000, Environment Canada held the first global Internet workshop on wind chill, with more than 400 participants from 35 countries. Almost all agreed on the need for a new international standard for measuring and reporting wind chill that was more accurate, easy to understand, and incorporated recent advances in scientific knowledge.

During 2001, a team of scientists and medical experts from Canada and the U.S. worked together to develop a new wind chill index. The research agency of the Canadian Department of National Defence, with its knowledge of how troops are affected by cold weather, contributed to the effort by conducting experiments using human volunteers.

The new index is based on the loss of heat from the face-the part of the body that is most exposed to severe winter weather. Volunteers were exposed to a variety of temperatures and wind speeds inside a refrigerated wind tunnel. They were dressed in winter clothing, with only their faces exposed directly to the cold. To simulate other factors affecting heat loss, they also walked on treadmills and were tested with both dry and wet faces.

To ensure the new wind chill index meets the needs of Canadians, Environment Canada conducted public surveys across the country. The new index is expressed in temperature-like units, the format preferred by most Canadians.

However, since the wind chill index represents the feeling of cold on your skin, it is not actually a real temperature, so it is given without the degree sign. For example, "Today the temperature is -10°C, and the wind chill is -20."

The new index is also being used in the U.S., so travelers will hear consistent information in both countries (although the U.S. Index will be provided on a Fahrenheit scale).

Listen for Forecasts and Warnings

Listen for the new wind chill index in Environment Canada's weather forecasts. In most of southern Canada, wind chill is included in the forecast when it reaches -25, the point where frostbite becomes a risk. A wind chill warning is issued when conditions become hazardous.

Weather forecasts are available through radio and TV broadcasts, as well as on Environment Canada's Weatheradio, recorded telephone messages, and on our web site at www.ec.gc.ca.

Further information

Environment Canada, Inquiry Centre
Ottawa K1A OH3
email: enviroinfo@ec.gc.ca
tel: 1-800-668-6767
Web sites:
  weather forecasts: www.weatheroffice.ec.gc.ca
  wind chill site: www.windchill.ec.gc.ca

Wind Chill Hazards and Thresholds
Cold Injuries
Factoids and Quiz

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