On August 11, a message that “there will be heavy rain in the city from the morning to the night of the 12th, it is suggested to work at home” was brushed on the screen of Beijing People’s mobile phone circle of friends. < p > < p > on the 12th, the whole of Beijing was watching the clouds and chasing the rain. At noon, the rainstorm in some parts of Beijing came late, but there was a gap with the original imagination. Some experts said that the rain at noon was not the main force. In the evening, the rain in Beijing arrived as scheduled. As of the press release, the average rainfall in the whole city has reached the moderate rainfall level, and local heavy rain or rainstorm. Experts from Beijing Meteorological Bureau said that due to the complexity and variability of the atmospheric system and the uncertainty of numerical prediction itself, with the current forecasting ability, it is often only possible to forecast the possible range of local severe weather in advance, but not the exact location of its occurrence in advance. “Local” in weather forecast is not a specific location, but to a certain extent, expresses the uncertainty of forecast and the possible extreme. Lan Yu, deputy director of the severe weather forecast center of the central meteorological station, told China Science Daily that the production of severe convective weather forecast is based on the physical mechanism of its formation, which is very complex, so comprehensive research and judgment based on various factors are needed. < p > < p > “severe convective weather has the characteristics of sudden and local, and the convective system often develops violently, which is easy to cause extreme disastrous weather in a short time.” Lan Yu pointed out that the triggering and evolution of severe convective system will be affected by many factors, such as background weather system, regional environmental conditions and their changes, which are closely related to local topography and geomorphology. As a result, the precise forecast of severe convective weather is still the field that meteorological experts all over the world are committed to tackling, and the accurate prediction of disastrous severe convective weather is still a huge problem Lan Yu said. Fu Jiaolan, a senior engineer at the central meteorological station, told China science news that “at present, it is basically possible to accurately forecast the area and intensity of strong precipitation about three days in advance, and the accuracy rate of 24-hour rainstorm warning in China can reach 89%.” According to Lan Yu, modern observation network, high resolution numerical model forecast and its interpretation technology, as well as forecasters’ first-line experience are the main technical means for severe convective weather forecast. The precise forecast of the intensity and time of severe convective weather depends on the joint application of the above support means. “< p > < p >” among them, the impact forecast especially needs to consider the special terrain, geological environment and urban economic and population distribution and other factors, which greatly depends on the organic combination of modern objective technology and forecaster’s subjective experience. ” Lan Yu explained. According to Lan Yu, strong convective weather forecast has distinct scientific and technological elements. First of all, the modern observation means of air ground integration, such as dense ground automatic station network, new generation Doppler weather radar observation network, and the application of China’s Fengyun series meteorological satellite data. Secondly, with the support of powerful computing resources (supercomputers), the kilometer scale high-resolution numerical model prediction and its interpretation and application are discussed. In addition, there are also objective analysis and forecast technology based on the understanding of severe convective weather mechanism and the application of artificial intelligence technology. According to Fu Jiaolan, the grapes-3km mesoscale model independently developed by China has provided technical support for heavy rainfall forecast. At the same time, the precision spatial resolution of the refined intelligent grid precipitation forecast developed by the central meteorological station can reach the resolution of 5km, and the time interval is hour by hour. At the same time, the precision of precipitation forecast can be continuously improved by rolling update according to the actual situation. Zhang Tao, chief forecaster of the central meteorological station, said that the heavy rainfall in the north is in the midsummer season, and the biggest feature is that the wind direction in the South China Sea in summer can reach the strongest force in the north. “This means that the influence range of the South low-level warm and humid air flow can reach the northernmost and the intensity can reach the maximum, which is a basic material condition for this rainfall.” In addition, due to the influence of Mongolia cyclone and high-altitude cold vortex, the cold air in the north is also relatively active. When the active cold air goes southward, it will encounter the northward monsoon and cause rainfall. In addition, the Western Pacific subtropical high moved westward and northward since November 12. “The three complement each other, that is, the subtropical high moves westward and northward, the South China Sea summer monsoon surges northward at low altitude, and the cold air from the north moves southward, which together result in large-scale precipitation in the north.” Zhang Tao said. It is estimated that there will be a precipitation process in northern China from 15th to 17th. Zhang Tao said that it is still difficult to judge whether the intensity of the precipitation process from 15 to 17 is equivalent to this one. Zhang Tao said that this year’s rainfall performance is more extreme, and compared with the annual average, it tends to be abnormal, mainly in the Yangtze River Basin during the Meiyu flood season. After that, the precipitation process in northern China may be more extreme.