When we’re outdoors, temperature means everything. Not just the temperature that our thermometers read and the weather forecasters say, but the temperature we actually feel. So, what is really going on when a strong gust of wind picks up out of nowhere and makes it feel like the the temperature dropped 10 degrees — even though the reading on the thermometer has not changed?
The sensation that the temperature in the presence of wind is colder than the temperature without wind is called wind chill. We are not just talking about “weather wind” because the air rushing over our skin during activities such as skiing or snowboarding, for example, can drop the felt temperature, too. Wind chill can put us at risk for frostbite or hypothermia more easily, so knowing about it can make a huge difference!
The intensity of the wind chill phenomenon really depends on two things:
- The “still-air” temperature (i.e., the temperature without considering the effect of wind)
- The wind velocity (i.e., how fast the wind is blowing)
Because our human bodies constantly give off heat, our skin heats the air around it. Consequently, the air right around our skin becomes warm and forms something similar to an invisible, heated “air jacket.” When wind blows, however, this warmer air around our skin gets quickly blown away and is replaced by the colder moving air of the wind. The faster the wind blows, the less of a chance we get to heat the air just around our skin. So, the colder we feel!
The National Weather Service chart to the right shows how given a “still-air” temperature and a wind velocity, you can estimate the temperature that you’re actually feeling because of the wind chill effect.
Fortunately, you can predict the temperature-dropping effects of wind chill pretty accurately by making your own “wind chill-o-meter” or, more formally, a wet-bulb thermometer. Here is what you need:
- A regular dry-bulb thermometer (e.g. mercury in glass)
- A hollow cotton shoelace
- A rubber band
INSTRUCTIONS: Cut off the plastic tip ends of the shoelace and spread apart the lace to create a narrow cotton tube. Put just the bulb of the thermometer into the tube of a shoelace, and secure it with a rubber band. Now, take the free end of the shoelace and place at least 3 in. of that end in a container of water. With the moisture contained and absorbed by the shoelace, this thermometer now models how we humans experience wind chill.
Try it out! Turn on a fan or swing your wind chill-o-meter around and notice how the temperature reading drops!