Weather system types of extreme precipitation in the middle reaches of the Yangtze river

Based on the conventional observation data, physical data and mesoscale observation data of 60 cases of extreme precipitation in Hubei province from May to September during 2008-2015, the mechanism of weather system evolution, the thermal and dynamic characteristics of the systems, and the reason for formation and maintenance of heavy rainfall are studied by means of weather diagnosis. Five types for weather systems of extreme precipitation are summarized: the frontal cyclone type, the southwest vortex and shear type, the southwest vortex-northeast cyclone type, the warm low pressure inverse trough type and the landing typhoon low-pressure type. The first two are the most important types of extreme precipitation. At the same time, the key points of weather forecast under different weather types are pointed out: (1) For the frontal cyclone type, the development of the Jiang-huai cyclone is an important disturbance system in Meiyu front. But it is not strong because the cold air force is weak, so the Jiang-huai cyclone can be easily ignored in routine weather analysis during Meiyu period. (2)For the southwest vortex and shear type, the southwest vortex, the nascent vortex and the low-level jet are important disturbances in the Meiyu front, and the difference of the precipitation area is related to the influence of the different disturbance systems. (3) The precipitation area of the southwest vortex-northeast cyclone type is generally located at the junction of two systems, and most of the extreme precipitation occurs only in the western part of Meiyu front. (4)The warm low pressure inverse trough type mainly produces local extreme precipitation. And the precipitation mostly falls in the transition zone from the western Hubei mountains to the west of Jianghan plain. (5) Landing typhoon interacts with subtropical high and forms a stable favorable situation, coupled with special terrain, which is the main reason for the development and maintenance of extreme precipitation.