Wind Chill

The "New" Wind Chill chart (2001). NOAA NWS

Definition: Wind chill is how cold it feels outside when wind speed is factored in with the actual air temperature. It is expressed as a temperature, and will always be lower than the actual air temperature.

The wind chill doesn't always exist. It only comes into play when air temperatures are 40°F (4°C) or less, and wind speeds are 3 mph or more. 

  • At a wind chill of -18 F, frostbite can occur in 30 minutes or less.
  • At a wind chill of -32 F, frostbite can occur in 10 minutes or less.
  • At a wind chill of -48 F, frostbite can occur in 5 minutes or less.

During the winter months, our bodies heat (through convection) a thin layer of air just next to our skin. This layer of warm air helps insulate us from the surrounding cold. But when the cold winter wind blows across our exposed skin or clothes, it carries this warmth away from our bodies. The faster the wind blows, the faster the heat is carried away. If the skin or clothes are wet, the wind will lower the temperature even more quickly, since moving air evaporates the moisture at a quicker rate than still air would.

Also known as: Windchill, Wind chill factor, 

MORE: What does sticking your finger in the air tell you about wind?