Earlier this summer, I wrote one of our first ‘weather why’ pieces on the heat index. Now that Eric has written the obituary for Summer 2016 (RIP), we can discuss the heat index’s winter cousin—the wind chill. Since regional wind chill temperatures could fall into the upper teens tonight, it’s important to understand how wind chill works.
What is wind chill?
Wind chill describes how cold the air feels against your skin, not the actual air temperature. Our bodies radiate heat out at all times, which is why we wear layers to trap our body heat in the cold. Without any layers to trap that heat, it radiates into the surrounding air. However, if the air is calm, that heat will hang out near your body, creating a thin, warm insulating layer near your skin.
When the wind begins to blow, it immediately draws that thin warm layer of air away–just like when you blow on hot soup to cool it down. Your body cools off more quickly, and in response, it generates more heat to stay warm. This process—your body working more to create heat, only to have that heat immediately blown away by the wind—will act to lower your skin and body temperature, and the air ‘feels’ colder.
How do we measure wind chill?
The wind chill is influenced by two factors, wind and temperature. As wind speed increases, the wind chill temperature decreases. For example, if tonight’s forecast low is 36°F, and the forecast wind speed is 12 mph, the calculated wind chill would be around 28°F. In this situation, keep in mind that as long as the actual air temperature is above 32°F, things won’t actually freeze. When temperatures are below freezing, however, wind chill can expedite the time it takes for hypothermia and frostbite to take effect.
We use the chart below to quickly calculate the wind chill (and note the formula the NWS uses to calculate these values, at the bottom of the graphic);
Preparing for the chill
When wind chills drop below freezing, you should prepare for outdoor activities just as you would for actual freezing temperatures. Your body will feel the same as if it were actually freezing, so dress in layers and cover up to prevent heat loss, stay dry, and stay inside. Don’t forget your pets, either!