WeatherWise

Wind chill adds to our winter misery

For people living in Canada or the northern tier of the United States, winter can bring miserable weather.

Snow as well as bone-chilling cold air can take up residence and never seem to leave. Then there is the “wind-chill factor,” an expression that frequently pops up on weather maps and is referred to quite often in weathercasts during winter.

So, exactly what are the “chilling facts” about wind chill? What is it and what kind of effect does it have on our lives?

Wind chill can be explained as a combination of winds and cold temperatures. It is how cold the air appears to be when the wind is blowing. Even though the wind chill is given as a temperature, it’s not really a different kind of temperature.

What it means in practical terms is that if the antifreeze in your car’s radiator is good to minus-12 degrees Celsius and the temperature drops to minus-6 degrees Celsius, you do not have to worry, even if your car is out in a 20 mph wind that drops the wind chill to minus-23 degrees. As long as the actual temperature does not fall below minus-12 degrees, the fluid in your car’s radiator will not cool below minus-12 degrees, no matter how hard the wind blows.

The term “wind chill” was coined by Antarctic explorers Paul Siple and Charles Passel after conducting experiments on the time needed to freeze water in a plastic cylinder exposed to the elements.

They found out that the time needed to freeze water, was dependent on how warm the water was, the outside temperature and wind speed. The reason for this experiment, theoretically, was to eventually determine at what rate the body loses heat when exposed to the cold and the wind so that the public would be able to protect itself from hypothermia, frostbite and other cold-related ailments.

A wind-chill index was created in the 1940s and had been used until closer inspection of the numbers revealed that the WCI was too cold and thereby wrong. The problem with the WCI was caused by the fact that human skin freezes at a different rate than water.

One person who recognized how wrong the WCI was Maurice Bluestein, a mechanical engineer. While shoveling snow on a day that saw a temperature of minus-32 degrees Celsius and a minus-75 degree WCI, Bluestein noticed that his exposed skin was not freezing in 15 seconds, as it should have done if the wind and the cold were the equivalent of minus-75 degrees Celsius.

After years of tinkering around with how to improve the index, it was not until the fall of 2000 that improvements finally took place on the old formula and in the fall of 2001 both Canada and the United States had incorporated the new WCI by posting them on their respective weather service Web sites.

The current formula uses advances in science, technology and computer modeling in order to provide a more accurate and useful formula in calculating winds and temperatures.

Here are some of the specifics:

*The new WCI calculates wind speed at an average height of five feet above ground (typical height of an adult human face) instead of a height of 33 feet above the ground;
*It is based on a human face model (how fast does human skin freeze instead of water?);
*It incorporates modern heat transfer theory (heat loss from the body to its surroundings, during cold and windy days).

As one can see, the science of meteorology gradually reshapes itself to keep up with the times. By improved computer modeling, the WCI now gives you the most accurate of information in order to protect yourself from the winter’s wrath.

So, the next time you are about to step out into the cold, turn on the television, watch the weather report and feel comfort in knowing that your local weatherman is not just blowing hot air.  

Scott Sumner is a member of the American Meteorological Society.