Many times, we look at the weather forecast and decide that it is a perfect day to go to the field, but afterwards we have much warmer than the meteorologist or the consulted application predicted. In these cases, the information we have seen does not have to be wrong. It is simply that the temperature in the prediction is not always what it actually feels.
On a regular basis, with the arrival of the internet and applications specialized in smartphones Y tablets, when it comes to knowing the weather in the next few days, we see another value other than the temperature that many people do not recognize or do not know how to identify. This represents the thermal sensation that, depending on various factors such as weather, altitude, time of day, season of the year or humidity, it can vary by a few degrees compared to the value that it marks. But what changes in the wind chill and what does each value affect? We see it.
What is temperature?
To better understand this topic, we must first understand the more fundamental concept of temperature. Basically it is the measure of heat and cold, that is, it is the degree of heat present in a substance that gives us that same sensation. At the molecular level, it is the average kinetic energy possessed by the atoms of a material. The larger it is in an object, the greater its kinetic energy. There are many units attributed to its measurement, but the most famous are Celsius, Fahrenheit, which is used mostly in the United States, and Kelvin, which is used mostly in Physics and Chemistry.
Temperature is measured with a thermometer and is based on the basic principle that liquids expand when heated and contract when cooled. Therefore, when this increases, the mercury expands and rises in the tube, and when it decreases, it contracts and does the opposite. These movements are compared to a reference point to obtain the value of the temperature readings.
What is the wind chill?
If measuring it consists of record air temperature From a thermometer that has been kept within a Stevenson screen or through the use of any other appropriate instrument, wind chill, on the other hand, is a calculated figure that considers several different factors other than air temperature. This value gives people a rough idea of how they will really feel if they go outside where the temperature has been recorded.
The other factors taken into account by wind chill are wind speed and strength, air temperature, area relative humidity, and the rate of heat loss from a human body when covered in clothing. When we combine all these factors and the average temperature of the surrounding area, the end result is the so-called thermal sensation, which in some applications is reflected with the Anglicism «Real Feel». So how do these factors change our perception of heat and cold?
Why does the wind make us feel colder than it really does?
For a moment, consider a gust of wind moving rapidly through the environment. Humans are warm-blooded living beings, and as a result, our bodies stay within a fixed range: 37 degrees Celsius. Now that heat that flows into the body is also transferred to the skin, which in turn warms the air around it. As the temperature difference between the body and the air is reduced, we feel warmer. What the wind does is blow away this layer of hot air, leaving our skin exposed to the colder air that surrounds us.
Why does humidity raise the temperature around us?
Humidity, another factor that changes our perception of temperature, operates in the complete opposite way. On a warm sunny day our body uses a very special process to cool our body: sweat. And sweat, that is, salty water with some minerals and ions, absorbs the heat from the surrounding air and evaporates from our skin, providing a refreshing sensation. This process is known as evaporative cooling. However, this is greatly reduced if the air around us is humid, as it already carries water. As a result, warm air and sweat remain on our skin, making us feel even warmer.
To measure wind chill, meteorologists use something called Heat index (HI), which combines air temperature and dew point or relative humidity to determine the equivalent human-perceived temperature. At 30 degrees Celsius, with 10% humidity, we feel closer to 26 degrees, but at 90% humidity, it will feel closer to 38.