It’s an sunny February morning and you turn on the TV to watch the local weather report. The meteorologist’s forecast says 30 degrees Fahrenheit, which doesn’t seem too bad. It’s winter after all! But then, you notice that the “feels-like” temperature is closer to 20 degrees. Suddenly, that extra cup of warm coffee and a fuzzy hat sound really nice.
That feels-like temperature can come in the form of wind chill or heat index, so similar scenes can play out during the dog days of summer. The amount of moisture in the air–or humidity–can make 80 degrees feel closer to 90.
“It’s basically just how the temperature feels different to our skin,” meteorologist Cyrena Arnold tells Popular Science. “We have sensors in our skin and our skin is made up of water. So our skin actually behaves differently based upon the evaporation of that water.”
Feels-like: wind chill
When the air temperature itself is cold and the winds are moving at a higher speed, it can pull more heat away from the body and cause the water on our skin to evaporate faster.
“In order for moisture to evaporate off of your skin, it takes heat. It has to absorb heat in order for those little water molecules on your skin to go from liquid to a gas,” says Arnold. “So when there’s a wind chill, it doesn’t take a lot of energy because of that wind and that cold for the liquid to go into the gas form.”
This increased evaporation speed and energy expenditure is also why hikers, skiers, first responders, or anyone staying outside in the cold for extended periods of time should avoid cotton clothing.
“Cotton is known for causing quick evaporation,” explains Arnold. “It’s a breathable fabric where wools and synthetics prevent some of that evaporation and help keep you warmer when it’s cold.”
While meteorologists u….
