How is the precipitation probability calculated in weather forecast?

Scientists are only 70% sure about precipitation. Probability is a mathematical term, and its intuitive meaning refers to the possibility of a thing happening. The prediction published in the form of probability is called probability prediction. On the days when the probability forecast is not released, if the certainty of precipitation is 70%, tell the citizens that there is precipitation in this city today, and say that only 70% of the probability is 100%. Therefore, it shows that the release of precipitation probability forecast is an improvement of precipitation forecast. In other words, the release of probability prediction is beneficial to public decision-making.

Popular understanding: under certain conditions (temperature, air pressure, humidity, etc. ), the probability of precipitation in history is 30%, so now meet these conditions, it can be said that the probability of precipitation is 30%. Of course, the coordination of meteorological conditions is very complicated, and it is impossible to have exactly the same conditions as in history. The general situation of precipitation probability forecast is sunny, and the probability of 0% is impossible to precipitation; Sunny to cloudy, the probability of precipitation is between 10%-20%, and the possibility of precipitation is very small; Cloudy, sporadic or local precipitation, when the probability is between 30% and 50%, there is a chance of precipitation; The probability of precipitation is between 60% and 70%, and the possibility of precipitation is relatively large; When the probability of precipitation is greater than or equal to 80%, the possibility of precipitation is great; If the probability of precipitation is 100%, precipitation will definitely occur. Speaking of precipitation, there is also a concept of precipitation. The meteorological department calls it rain and snow precipitation, and precipitation is called precipitation. The unit of precipitation is usually millimeters. 1mm precipitation refers to the water depth per unit area1mm. 1mm How much precipitation has fallen into the fields? As we know, the area per mu is 666.7m2, so the precipitation of 1mm is equivalent to an increase of 0.667m3 of water per mu. Every cubic meter of water is 1000 kg, so the precipitation of 1 mm is equivalent to watering about 650 kg of water per mu.

The calculation of precipitation probability forecast is actually whether it is precipitation or not, which is related to the variation law of precipitation itself and the characteristics of meteorological elements. By analyzing the data of various meteorological elements and using the principle of statistical calculation, scientists have obtained many equations for predicting precipitation probability, such as the method of predicting precipitation probability with precipitation data and the equation of predicting precipitation probability the next day with pressure, temperature and humidity of the day. When constructing these equations, we can also use the products of numerical weather forecast. Of course, there are some more complicated forecasting methods. Because the probability forecast only means that there is a certain possibility of a certain weather, and the probability of forecasting precipitation is 30%, when arranging activities, it is necessary to give priority to no rain and make proper preparations for rain; The probability of forecasting precipitation is 60%, and the activities are mainly rainy, supplemented by no rain; The probability of forecasting precipitation is 80%, so be prepared for rain.