The weather forecast in Zhangye 15 days is accurate. Will there be frost tomorrow?

Therefore, the various predictions made by the weather forecast can only be a kind of "probability". For example, under a certain temperature, pressure and humidity, it rains 20% of the time in history, and the meteorological observatory will think that the probability of rain is 2% and it is unlikely to rain. Combined with other data, when the weather forecast is broadcast, it may be said to be cloudy for people's convenience, but whether it will rain in the end depends on God's mood.

So what factors will affect the accuracy of weather forecast? According to the summary of meteorologists, there are generally the following four points:

First of all, human understanding of the mechanism of atmospheric motion is still limited. Cloudy days, cold days, rain and snow, wind and frost, all kinds of weather are caused by the constant movement of the atmosphere. Because of the complexity of atmospheric motion, scientists can't really describe the fine structure of atmospheric motion.

Secondly, the meteorological observation network cannot be "sparse but not leaking". Meteorological exploration has developed into a three-dimensional observation system covering the ground, air and space. Ground observation stations, high-altitude observation stations, automatic weather stations, radar observation stations and weather stars form an observation network to continuously monitor atmospheric movements and changes.

But this net will miss small and medium-scale weather systems, just like catching small fish in a big net, it is easy to miss. Moreover, there may be errors in the observation data. For example, the observation results of wind direction and speed are all 2 minutes average, and there may be errors.

Thirdly, the numerical weather forecast model can't fully simulate the atmospheric evolution. The change of weather is the result of the change of atmospheric motion around the earth, which should conform to some laws of fluid mechanics and thermodynamics in physics. These laws can be written into mathematical equations in mathematical language.

People use high-performance computers to turn the problem of weather forecast into the problem of understanding mathematical equations. This method is called numerical weather forecast, which is the core of modern weather forecast. However, at present, any set of models can not truly simulate the evolution of the atmosphere, but only approximate, and there must be errors.

Fourth, there will be differences in experience and level between forecasters. The forecast results calculated by the numerical model cannot be directly used as the forecast conclusion, and forecasters have to interpret, apply and correct them according to local conditions. For example, there is Yanshan Mountain in the north and Taihang Mountain in the west of Beijing, so the weather forecast must consider the influence of topography. The personal experience of forecasters also plays an important role in the prediction and comprehensive decision-making of complex weather.