Abstract:In the early morning of 7 July 2016, due to the influence of mesoscale convective system (MCS), a sudden local rainstorm occurred in Nanjing. Development of the MCS including convection triggering, quasi-stationary backward propagation, heavy rainfall supercell and cold pool driving lasted for nearly 8 hours, resulting in serious waterlogging. The synoptic background and MCS evolution characteristics of this heavy rainfall process are analyzed in detail by using multi-source datasets from Doppler radar, automatic stations, wind profile, China regional reanalysis (CNRR), Jiangsu merged assimilation analysis and so forth. The results show that a mesoscale forward-tilting trough induced low pressure at the surface, strengthening convergence, forming an uplifting movement and triggering linear convective storms. The warm and humid southwesterly flow between 3 km and 6 km was significantly enhanced. The favorable configuration of the uplifted left side of meso-β scale secondary circulation, the meso-γ scale low-level low pressure and the southwesterly flow made the MCS over Nanjing exhibit a quasi-stationary feature of backward propagation, eventually leading to a heavy precipitation supercell in eight consecutive radar volume scans. The drag effect of heavy precipitation formed a downdraft, which led to the outflow near the surface and stimulated a new convection on the south side, causing the MCS to move slowly to the south. As the downdraft strengthened in the MCS, a cold pool appeared on the ground. The strong divergence accelerated the movement of the MCS, and then the heavy precipitation process ended.