How is the weather temperature measured?

I agree with upstairs that there are two concepts of temperature: dry bulb temperature and wet bulb temperature.

A pair of thermometers with the same shape are used in the parallel device, one is used to measure the temperature, which is called a dry bulb thermometer, and the other is wrapped with absorbent gauze soaked in distilled water, which is called a wet bulb thermometer. When the air is not saturated, the wet bulb needs to consume heat due to surface evaporation, thus reducing the temperature of the wet bulb. At the same time, the wet ball continuously gets heat supply from the air flowing through the wet ball. When the heat consumed by evaporation of the wet bulb is in balance with the heat obtained from the surrounding air, the temperature of the wet bulb will not continue to drop, resulting in the temperature difference between the dry bulb and the wet bulb. The temperature difference between dry bulb and wet bulb is mainly related to the air humidity at that time. The smaller the air humidity is, the faster the water on the surface of wet bulb evaporates, the more the temperature of wet bulb drops, and the greater the temperature difference between dry bulb and wet bulb. On the contrary, the greater the air humidity, the slower the evaporation of water on the surface of wet bulb, the smaller the temperature drop of wet bulb and the smaller the temperature difference between dry bulb and wet bulb. Of course, the temperature difference between wet and dry balls is also related to other factors, such as ventilation speed, air pressure, wet ball size, wet ball wetting mode and so on. According to the temperature values of dry and wet bulbs and considering other factors, the air humidity at that time can be calculated theoretically. Dry wet bulb thermometer is the main instrument for measuring humidity at present, but it is not suitable for low temperature (below-10℃).

This is why the predicted temperature always feels lower than the actual temperature.