Why is it that sometimes the weather forecast is wrong and it says it will rain, but it doesn't rain at all?

Because the weather system is a very complex system, the principle of prediction is that, for example, if we know the initial state of a system and how it changes, we can infer its change at a certain moment by using a corresponding change quantity.

For example, if you know that a person is on the runway 100 meters and runs 10 meters every second, then he should be at 200 meters after 10 seconds. This is the weather forecast.

But the weather system is not static. There is a word called butterfly effect, which is about the complexity of weather system. If you are interested, you can go to Wikipedia to see the meaning of this word. In a word, the weather system is a nonlinear system, and the influencing factors are so complex that it is completely beyond the computing power of large computers. Therefore, in the actual forecast, only some factors can be considered or simplified in the calculation, so the forecast is not absolutely accurate.

The weather forecast of the meteorological station is divided into regions. There are many counties, districts, townships, towns and villages in this area. It is predicted that there will be rain in this area, maybe it will rain in the whole area, maybe it will rain in some places, and it will not rain in some places. So it's not that the weather forecast is inaccurate, but that the area is too large. In addition, climate change is changing rapidly.

Weather forecast is to collect data through various devices, such as radar and satellites. Then use a supercomputer to analyze and calculate the future weather trend with a certain algorithm.

Because it is calculated, according to the nonlinear relationship, a little error can make a huge difference, so the weather forecast can only predict the short-term weather situation, and the long-term weather forecast may be completely inaccurate. There is a physics book "Chaos" about the related things caused by this phase.

The prediction of temperature is to predict the high-altitude temperature 200 meters above the surface. So the general temperature is not allowed.