What is Apparent temperature or felt temperature?

National meteorological services and the principle of "perceived temperature"

In 2008, the national meteorological services institute introduced the principle of "apparent temperature" to go a step further than the measured air temperature and include other weather elements. The aim was to be more precise about the notion of temperature.

The purpose of this temperature measurement is to gain a better understanding of the human body's temperature concerning various climatic factors. Highly publicised especially during periods of extreme cold or heatwave the principle of felt temperature only concerns the temperature that the human body feels outside and in a place not protected from the wind.

In North America, and in particular, in Canada, apparent temperature also exists, but it is called "Wind Chill". Indeed, the cold is much stronger there than in France during the winter!
Humidex and wind chill: when air temperature is not enough
To calculate the temperature, national meteorological services and the weather measuring devices take into account the air temperature and add other elements, such as the humidity level or the wind speed.
This is called humidex the index integrating the combined effects of heat and humidity, and the wind chill, which takes into account the impact of the wind on the apparent temperature.

The humidex index combines air temperature and relative humidity

As you may have noticed, heat is more aggressive to the body when humidity is high. This climate is known as 'tropical' and causes a feeling of unease: this is often what happens during heatwaves, which occurred in France in 2018 and 2019. Temperatures are high (often over 30 degrees) and high humidity makes the air suffocating.
The humidex index was created and is used by Canadian meteorologists and takes into account 2 factors: the temperature in degrees and the relative humidity.
To illustrate the humidex index with a concrete example, let us take the case of a temperature of 30 degrees and relative humidity of 70%. In this weather configuration, the humidex index would be 41. Careful, it's not a temperature in degrees! This is a hint.

Wind chill combines the effects of wind with ambient temperature

As for the cold, it becomes more acute for the body because of a phenomenon that accentuates it: the wind. The wind chill is also an indication. This is also often the scientific phenomenon behind the term "apparent temperature" in everyday language. The temperature felt in France is often lower than the actual temperature.
Wind chill is therefore used to express the cold sensation produced by wind on the heat-producing human body. If it feels like the temperature is dropping, it's just the wind producing that effect. The "real" temperature" remains the same.
Let's take an example: with an air temperature of -10 degrees and a wind speed of 30 km/h, the wind index will be -20. But we are not talking about degrees here, it is only a number without a unit of measurement, an index. This however gives an idea of the temperature in degrees.

Humidex and wind chill: when air temperature is not enough

To calculate the temperature, national meteorological services and the weather measuring devices take into account the air temperature and add other elements, such as the humidity level or the wind speed.
This is called humidex the index integrating the combined effects of heat and humidity, and the wind chill, which takes into account the impact of the wind on the apparent temperature.

The humidex index combines air temperature and relative humidity

As you may have noticed, heat is more aggressive to the body when humidity is high. This climate is known as 'tropical' and causes a feeling of unease: this is often what happens during heatwaves, which occurred in France in 2018 and 2019. Temperatures are high (often over 30 degrees) and high humidity makes the air suffocating.
The humidex index was created and is used by Canadian meteorologists and takes into account 2 factors: the temperature in degrees and the relative humidity.
To illustrate the humidex index with a concrete example, let us take the case of a temperature of 30 degrees and relative humidity of 70%. In this weather configuration, the humidex index would be 41. Careful, it's not a temperature in degrees! This is a hint.

Wind chill combines the effects of wind with ambient temperature

As for the cold, it becomes more acute for the body because of a phenomenon that accentuates it: the wind. The wind chill is also an indication. This is also often the scientific phenomenon behind the term "apparent temperature" in everyday language. The temperature felt in France is often lower than the actual temperature.
Wind chill is therefore used to express the cold sensation produced by wind on the heat-producing human body. If it feels like the temperature is dropping, it's just the wind producing that effect. The "real" temperature" remains the same.
Let's take an example: with an air temperature of -10 degrees and a wind speed of 30 km/h, the wind index will be -20. But we are not talking about degrees here, it is only a number without a unit of measurement, an index. This however gives an idea of the temperature in degrees.

How reliable is the temperature you feel?

However, the principle of apparent temperature is questioned by some meteorologists, who believe that it is not a reliable index. So what is it?
While the classic temperature expressed in degrees is perfectly reliable, this is not necessarily the case for felt temperatures. Indeed, being calculated on an index basis, they include a degree of variability and can be measured differently in different cases.
By measuring the data (humidity, wind, and temperature) at slightly spaced locations, the perceived temperature can easily vary.
It is an interesting index that provides high-quality information. But it is not as accurate as other weather data!