Windchill is a measure of how cold people and animals feel based on heat loss due to wind and evaporation. In cold and windy weather conditions, the skin loses heat through evaporation much more quickly than if the wind were not blowing. Therefore, it feels much cooler when it’s cold outside and the wind is blowing. The faster the wind blows, the greater the evaporation and thus, the greater the chilling affect. This is called windchill, “real feel”, or apparent temperature.
There are a few misconceptions about windchill. The first is humidity does not noticeably affect a windchill reading. In fact, in the newest formula used by the National Weather Service, the humidity reading was left out.
The second misconception is inanimate objects such as metal, steel, wood and plastics experience windchill just like we humans do. This isn’t true. The only affect a cold wind has on these objects is that they cool off faster than had there been no wind. So as an example, if it’s -10°F outside with a -35°F windchill, the metal flag pole will only cool to -10°F, but it will do so more quickly than had the wind not been blowing. The flag pole will not get any colder than the air temperature, no matter how fast the wind blows.
Lastly, windchill only applies when it’s 50°F or colder outside and when the wind is blowing greater than 3 mph. If it’s warmer than that, or the wind is blowing slower than 3 mph, there is not windchill factor.
For us humans and animals, the windchill can greatly decrease the time for which frostbite and hypothermia kick in. If your skin happens to be damp or worse yet wet, the times decrease much more quickly. This is why it is extremely important not to overexert yourself and sweat when it is very cold outside, and you don’t want to run around excessively trying to stay warm. The sweat on your skin can make you cool off much more quickly and you may find yourself in big trouble.
There is no clear cut temperature verse time relationship for frostbite as it varies on many different factors. But in order for one to suffer from frostbite, the temperature must be below 32°F (freezing). That’s because frostbite is what happens when skin freezes, and eventually dies. Strangely, if the temperature is above freezing, but the windchill is below freezing, frostbite can occur. As a general rule, the below values can be followed:
- Wind chill of -20°F means frostbite in 30 minutes.
- Wind chill of -35°F means frostbite in 10 minutes.
- Wind chill of -55°F means frostbite in 5 minutes.
Hypothermia sets in when the core body temperature drops below 95°F and can occur at temperatures much greater than freezing. Wind chill will cause a person to loose body heat at an accelerated rate and as a result, can cause the core body temperature to drop very quickly.
A windchill calculator can be found here: NOAA