Wind Chill: What Is It, and How Is It Different from Normal Temperatures?

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WindChillChart

Often in the winter time, many meteorologists talk not just about temperature, but also the “wind chill”. It may seem that the wind chill is a made-up term, but contrary to popular belief (and as hilariously described by Bill Engvall — I just love his album Dorkfish), the wind chill factor has its roots in science.

History of the Wind Chill

2pm Monday Temperatures

2pm Monday Temperatures

This winter weather staple would not be well-known if it weren’t for an Antarctic Expedition that spanned from 1939 to 1940. During that time, Charles Passel and Paul Siple observed that water contained within a pyrene container would take a longer time to freeze during calm winds, but it would freeze in a short amount of time during periods of swifter wind speeds.

 

The scientists continued to observe various temperature and wind speeds as well as water-freezing times, and through the results they developed the “wind chill factor” that indicated the amount of time needed to freeze water given a set temperature and wind speed. This was an important application to develop, given that the human body consists of approximately 60% water.

 

2pm Monday Wind Chill

2pm Monday Wind Chill

For decades, the wind chill “equation” developed by Passel and Siple was used, though people began to notice that the conversions were flawed. For example, a day in which above freezing temperatures but higher winds produced sub-freezing wind chills would certainly be less impactful on the body than a day in which the weather consisted of sub-freezing temperatures but little to no wind.

Additional research was needed, and in July/August 2001, twelve volunteers agreed to serve as subjects within the new study. They were hooked up to bio-sensors that measured everything from their internal temperatures to the heat flow from their noses, foreheads and cheeks as they walked on a treadmill for 90 minutes, during which they were subjected to cold air blowing on them at various wind speeds. From this research, the current wind chill equation was developed.

(Side note: Check out Popular Mechanics’ more detailed but “easy to read” historical account of this research. For die-hard scientists, the complete report is available from NOAA’s Office of the Federal Coordinator for Meteorological Services and Supporting Research. Be sure to scroll to page 36 to get to the meat of the research.)

Wind Chill and Winter Weather Safety

Keep in mind that the human body maintains a temperature of roughly 98.6 degrees Fahrenheit, and the body is emitting this heat to the air that surrounds it at all times.

On cooler days with no wind, the body will produce a layer of warmer air around it, effectively producing a temperature buffer from human warmth and the ambient cold. Once the wind begins to blow, that buffer of warmer air blows away from the body; it then has to work harder to stay at its 98.6 degree temperature level, or else it begins to cool — which is a dangerous situation for humans. In fact, two life-threatening conditions can develop during cold, windy days: hypothermia (which is a dangerously low body temperature, usually 95 degrees or below) and frostbite (which occurs when the water within the cells in your skin and other tissues literally freeze).

Essentially, the wind chill is a function of temperature and wind speed, and it serves to provide information as to how “cold” it is outside, especially regarding the amount of time it takes water to freeze. Interestingly enough, the terms “wind chill” and “feels like temperature” are different and not interchangeable. The “feels like” method also takes into account the changes in “feel” due to humidity.

Keep this in mind the next time you hear a meteorologist talk about the “wind chill”!

– Christina Edwards

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