Measuring wind chill
11th February, 2015
There is a good chance, especially during winter months, that you will have seen a weather forecast in which the forecaster predicts the temperature and then goes on to talk about the ‘wind chill factor’. This is because the temperatures we see on TV and published in newspapers represent the temperature of the air, but do not take into account how we actually experience the temperature.
When a forecaster goes on to talk about wind chill, or the ‘feels like’ temperature as it is also commonly known, they are referring to the temperature felt by the body on exposed skin. This is calculated by taking into account a number of factors, including:
- Relative humidity
- Wind speed at 5 feet (average human head height)
- How the body loses heat on a cold day
As an example, the air temperature here at our offices in Saxmundham in Suffolk this morning is currently 4°C. However, if we were to step outside, the temperature we would feel on our skin would be closer to 2°C.
Did you know? Kugaaruk in Canada is the location of the coldest ever recorded wind chill. On 13th January 1975 a wind chill of -92°C (-134°F) was calculated based on an air temperature of -51°C and a 35mph wind speed.
How Is Wind Chill Measured?
How Does It Impact Upon Us?
The core temperature of the human body is approximately 37°C and the air around us is usually below 37°C. This means that we will lose heat from anywhere not covered by clothing. On a windy day the speed at which moisture evaporates from our skin increases, moving heat away from our body and making it feel colder than it actually is.
The way in which wind chill is measured is a controversial topic. Some experts believe that it should be calculated based on whole body cooling whilst either naked or wearing appropriate clothing; while others believe it should be based on local cooling of the most exposed skin, such as the face. In 2008 the UK adopted a new system, known as the Joint Action Group for Temp Indices (JAG/IT). This system measures the wind chill based on how much heat is lost from a person's bare face whilst they are walking at 3mph.
So the next time you go outside and it feels colder than you were expecting, it is likely to be the result of wind chill!