What does the weather forecast mean by 10%?

Weather forecast is to predict the weather conditions in a certain period in the future by applying the law of atmospheric change and according to the current and recent weather situation. It is based on the analysis of satellite cloud images and weather maps, combined with the comprehensive study of meteorological data, terrain and seasonal characteristics, and mass experience.

If the weather forecast is rain or snow, a percentage number will appear next to the raindrop or snowflake icon, representing the probability of rain or snow. If the weather is sunny or cloudy, there is no such percentage. Usually, this forecasting form can better meet the decision-making needs in economic and social activities. But it only predicts the probability of rainfall or snowfall, and it cannot guarantee 100%.

numerical weather forecast

The so-called numerical weather forecast is to calculate the weather with a computer and let the computer tell us the changing situation. Because the atmospheric motion follows some known physical laws, the state of atmospheric motion can be written as a set of mathematical equations. Given the initial value of this set of equations, that is, the current state of the atmosphere, the variable values of this set of equations that change with time can be solved, and the future state of the atmosphere can be obtained.

From Copernicus, Kepler to Newton, the celestial mechanics method for predicting astronomical phenomena was gradually formed, based on Newton's discovery of gravity. Under the action of this force, celestial bodies follow Newton's law of motion-force equals mass times acceleration, which is the basic physical law that we all learned in middle school. Firstly, the gravitational force is calculated according to the mutual position of celestial bodies, so that the acceleration of celestial body movement can be calculated and obtained. Then, according to the observed current position and current moving speed of the celestial body, the new position and moving speed of the celestial body at any time in the future are calculated, so as to calculate the spatial trajectory of the celestial body movement step by step. It is assumed that the trajectory of air particles can be calculated by a method similar to the trajectory of celestial bodies, and the future atmospheric state can be determined by the trajectory of these particles, thus predicting the future "weather". This is the basic idea of numerical weather forecast.

The atmosphere surrounds the earth and changes every day. Although the movement of the atmosphere changes rapidly, it also has certain regularity. All weather changes are generally the result of energy accumulation, release and transformation in atmospheric movement. It follows a series of laws of natural physics, and can solve the equation by mathematical method according to the atmospheric state observed at a certain moment, so as to get the atmospheric state at a certain moment in the future, that is, the state of "weather".