In order to learn more about the performance of convective-scale ensemble forecast system for precipitation prediction in the Sichuan-Chongqing region, the control forecast (CNTL), the ensemble mean (MEAN) and the probability-matched ensemble mean (PM) of convective-scale ensemble prediction system are comprehensively analyzed based on daily precipitation data collected at 7 213 stations in the Sichuan-Chongqing region in warm season (from May to September) from 2020 to 2021, and differences between rainfall forecasts starting at 08:00 and 20:00 are compared. Results are as follows: (1) The forecast performance of PM and MEAN is better than that of CNTL. MEAN is skillful at forecasting moderate rain and heavy rain, and PM has obvious advantages for large rainfall. (2) Positive forecast deviations of light rainfall frequency are obvious in the whole research region, while for moderate rain and above, positive deviations are concentrated in high-altitude mountains such as the Daba Mountain, the Huaying Mountain and the Wuling Mountain, and negative deviations are mainly located in the Sichuan Basin and hilly areas. Positive (negative) deviations of light rain and moderate rain (heavy rain and rainstorm) predicted by MEAN are more obvious than those predicted by CNTL and PM. (3) The critical success index (CSI) and probability of detection (POD) scores with lead time of 36 h for the forecasts starting at 08:00 are higher than those with lead time of 48 h for the forecasts starting at 20:00, but the overestimation of rainfall frequency starting at 08:00 is more obvious in high-altitude mountains. (4) Compared with CNTL, PM and MEAN are better for the rainfall area of the heavy rain process from September 4 to 7, 2021 in the Sichuan Basin, which is related to the fact that ensemble forecast can better capture the position and morphology of the weather system.

Based on the conventional observation data, NCEP reanalysis data, satellite and Doppler radar data, a southwest vortex rainstorm process in Sichuan-Chongqing region from August 16 to 18 in 2015 was analyzed. The results indicate that the Tibetan Plateau vortices moving eastward and the cold air invading into Sichuan Basin contributed to the development of southwest vortex, and finally led to the heavy rainfall occurring under the relatively stable circulation background at middle-high latitude and low latitude in Asia. At the primary formation stage of southwest vortex, a cold front intruded on the northeast side of the surface thermal low pressure, a warm front formed on the north side of the center and the Southwest vortex was close to the positive pressure. At the stage of stable and sustainable development, the south part of the cold front moved to the south side of the low pressure, and the north part combined with the warm front to form a quasi-stationary front. The baroclinic property of the low vortex was obvious and nearly circular, and the continuous rainstorm mainly appeared near the warm shear line of the southwest vortex and the east side of the cold trough. At the weakening stage of southwest vortex moving eastward, the cold air invaded again, the cold front continued to strengthen, and the southwest vortex moving eastward deformed and weakened. The convergence at low-level, divergence at high-level, abundant water vapor transmission and accumulation of unstable energy played an important role in the deepening and development of southwest vortex and the maintenance of heavy precipitation. The convective clouds which developed near the warm shear line and the cold trough on the south side of low vortex led to the rainstorm. The heavy precipitation mainly occurred in the region with relatively large TBB gradient on the windward side of the cloud cluster. The local circulation of the heavy precipitation was composed of low level jet and shear lines or convergence lines. The wind vector of  wind inversion based on VVP (velocity volume processing) could more intuitively judge wind direction and speed, development stage of weather system, convergence line and shear line. The evolution of low-altitude convergence line, shear line and the intensity and direction of low level jet had important guiding significance for the dynamic conditions, maintenance time and echo extrapolation prediction of heavy rainfall weather.