In the summer months it is not unusual for thermometers to exceed 50ÂşC. However, can we really trust these readings? Is this temperature really accurate? The temperature gauges found on our nation's streets cannot be trusted as an accurate indicator of the day's temperature. When exposed to prolonged sun exposure, they register temperatures significantly higher than the actual measurement.
Do street thermometers measure temperature well?
Temperature readings provided by various thermometers located throughout the city, including classic free-standing ones as well as those found on bus stop shelters or in vehicles, are known to give inaccurate temperature values.
Besides direct sunlight, cities introduce another element that contributes to the heat: the heat emitted by asphalt and buildings. Can street thermometers be trusted?
As these urban thermometers absorb solar energy, they continue to accumulate heat until they reach their maximum capacity. At this point, a reverse process occurs, causing the buildings and asphalt to emit heat. This additional heat contributes to amplifying the temperatures detected by the urban thermometers' sensors.
It is important to note that thermometers placed in the sun in urban areas do not serve as accurate temperature reference points. For the most accurate readings, thermometers should be placed in shaded areas and open spaces free of buildings or asphalt, which will allow for better adjustment to the actual temperature.
Street thermometers, due to technical limitations, do not meet the standards set by the World Meteorological Organization. In contrast, mobile weather apps rely on sources that comply with these regulations.
What is the proper method to measure outdoor temperature?
The measurement of temperature in the street is carried out according to a set of standards established by the World Meteorological Organization (WMO), also known as WMO in English. To ensure accuracy, temperature is measured inside weather boxes, which are wooden structures painted in a waterproof matte white. These boxes are designed with walls arranged in the form of blinds.
The goal is to protect the thermometer from direct sunlight and measure the temperature of the surrounding air , rather than the thermometer itself. By implementing this configuration, the thermometer avoids absorbing moisture during rain while still allowing unrestricted airflow.
To ensure proper placement, the stand must be located at a minimum height of 1,20 meters above ground level, with a clear radius of at least 20 meters free of any obstructions . Furthermore, it is essential that the stand be located outside urban areas, with its entrance facing north.
The temperatures indicated by street thermometers cannot be considered reliable since they do not meet any of the necessary requirements.
How does the AEMET measure temperature?
The State Meteorological Agency (AEMET) of Spain measures temperature using a network of meteorological stations distributed throughout the country. These stations are equipped with specialized sensors that capture temperature data accurately and continuously.
The primary instrument used to measure temperature is the mercury or alcohol thermometer, housed in a weather station. However, these have now been largely replaced by electronic sensors due to their greater accuracy and ability to transmit data in real time . These sensors are resistance temperature detectors (RTDs) or thermistors, which measure temperature based on changes in electrical resistance as the temperature varies.
To ensure that temperature measurements are representative and not influenced by external factors, the sensors are placed inside a weather shelter. This shelter is a small, white structure that protects the sensor from sun, rain, and wind, while still allowing air circulation. The shelter is typically located 1,5 meters above ground level, an international standard height for air temperature measurement.
The AEMET weather stations record the temperature at regular intervals, which can vary between every 10 minutes and an hour, depending on the season. This data is automatically transmitted to AEMET processing centers, where it is analyzed and validated to ensure its accuracy. If anomalous data is detected, it is manually reviewed to confirm its veracity.
The collected temperature data is used for various purposes, such as making weather forecasts, monitoring extreme weather conditions, and studying long-term weather patterns. This data is also made available to the public, researchers and other institutions for analysis and decision making.
Thermal sensation and street thermometers
In the end, what really matters is the thermal sensation we have and not the number on a street thermometer. While actual temperature reflects the amount of heat in the air, wind chill takes into account other factors that influence our perception of that temperature, such as wind, humidity, and solar radiation.
Understanding wind chill is essential for correctly interpreting weather conditions and making informed decisions about what to wear or how to plan outdoor activities . For example, a temperature of 10°C on a sunny, windless day might feel comfortable, while the same temperature on a windy day could require warmer clothing.
In winter, low wind chill can increase the risk of hypothermia and frostbite, while in summer, high wind chill can lead to heat stroke or dehydration. For this reason, meteorological services such as the AEMET regularly provide information on thermal sensation along with actual temperatures and this is more important than looking at street thermometers.
I hope that with this information you can know if the street thermometers measure the temperature well or not.