Abstract:Using the precipitation data of dense automatic weather stations, ERA5 reanalysis data and radar data, we analyze a local rainstorm process influenced by the parallel ridge-valley topography in western Chongqing from 16 to 17 June 2020. The results show that the rainstorm process happened under the combined influence of the stable low vortex shear formed by the southwest warm and humid low-level airflow around the subtropical high and the northward air flow intruding into the Sichuan Basin under the guidance of the high trough in western Chongqing, and the maintaining mesoscale convergence line under the influence of the parallel ridge-valley topography. From 00 UTC to 03 UTC 17 June 2020, there existed obvious moisture convergence, ascending motion and strong instability center in the boundary layer below 850 hPa in the ridge-valley region, which triggered the localized severe heavy rainfall. Due to the ridge-valley topography, the cold front and the convergence center moving northward along the convergence line lifted on the windward slope, strengthening the vertical ascending motion that enhanced the vertical circulation wind speed ahead of the front. This is an important cause for the rainstorm amplification in the southern end of Huaying Mountain and the eastern transition area of wide valleys and hills. The development and evolution of the mesoscale convective systems were closely related to the postion change of the surface convergence line. The convergence uplift of the parallel ridge-valley made the mesoscale convective systems stagnate near the Huaying Mountain and strengthen twice at its southern end.