How does wind chill work? Strong gusts can create deadly conditions, weather expert says

On Oct. 26, hurricane-force northeasterly winds tore over California’s Sierra Nevada mountaintops and through the higher-elevation mountain passes toward the Pacific Ocean.

The Chair 6 Ridge anemometer, on top of Kirkwood Mountain with an elevation of 9,186 feet, south of Lake Tahoe, reported sustained northeasterly winds of 110 mph with 140 mph gusts at 9:15 a.m.

Sustained winds of 96 to 110 mph are classified as Category 2 hurricane on the Saffir–Simpson wind scale.

At the time of these wind measurements, the air temperature was a frigid 22 degrees Fahrenheit. After I posted these wind speeds on Twitter and Facebook, a couple of readers asked what the wind chill temperature would be with conditions like these.

Winds like these would rapidly take your body’s heat away, and here is why.

As warm-blooded mammals, we are continually transferring thermal energy to the atmosphere through conduction, convection, and thermal radiation.

Conduction is the transfer of heat through the material in direct contact with another body, like a cast-iron skillet on an electric stove.

Air is a wonderful insulator from the cold. In fact, it is one of the better ones we know of because it is a gas.

In a gas, molecules and atoms are spread out considerably farther than a substance in a solid or liquid phase such as water. Hence, gases reduce heat transfer due to conduction.

Swimming offers an excellent example of this physical property. If submerged in 70-degree water, most of us would feel cold after a few hours. In fact, some of us would become hypothermic within an hour!

On a frigid and blustery day, the thin boundary layer of heated air in contact with your skin and the thermal energy it contains is whisked away by the wind replaced with colder air. We call this process convection, which simply means “movement.”

Theoretically, you could be on top of a snow-covered mountain on a sunny and dead-calm day, absorbing the sun’s heat through thermal radiation. Without any wind to take your thermal energy away, you would probably feel entirely comfortable in shorts and a T-shirt despite well below freezing temperatures.

On Oct. 26, it was an entirely different story on the top of Kirkwood Mountain as the fierce winds blew.

To calculate wind chill, the National Weather Service has an online Wind Chill/Temperature Index calculator at www.weather.gov/oun/safety-winter-windchill.

When you enter 22 degrees Fahrenheit with 110 mph sustained winds, the wind chill temperature is 6 degrees below 0.

Both the heat and wind chill indexes are an apparent or perceived temperature.

The heat index measure is how hot air feels against your skin due to lack of evaporation; it can be much higher than the actual air temperature.

On the other side of the comfort scale is the wind chill index, and it is based primarily on wind speed versus relative humidity for the heat index.

Winds combined with cold temperatures can lead to potentially dangerous consequences such as hypothermia, frostbite and even death.

When your body becomes cold, it has mechanisms to maintain its core temperature.

For example, shivering activates muscles and generates heat. Goosebumps cause the hair on your skin to extend upward and partially block the wind.

In extreme hypothermia cases, your body restricts blood flow to extremities to maintain 98.6 degrees Fahrenheit in its core.

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