Abstract:One squall line influenced by the southwest vortex occurred in the eastern part of Sichuan Basin from the night of 4 June to the day of 5 June 2019. Using multi source observation data and ECMWF Reanalysis data, the characteristics and formation of the squall line are analyzed. The results show that convective heavy rainfall before the occurrence of the squall line was formed in the central Sichuan Basin under the background of the high altitude trough and the warm southwest vortex, combined with troposphere atmospheric environment of the deep wet layer and certain convective available potential energy (CAPE). The squall line occurred during the prominent frontogenesis process of cold front which surmounted the Qinling Mountains and entered the rear of the southwest vortex. With the joint influence of the high altitude trough, southwest vortex and strong cold front, the cold front vertical circulation merged with the southwest vortex vertical circulation, and the combined vertical circulation circle significantly strengthened the uplift mechanism of the frontal zone, which provided favorable dynamic lifting conditions for the formation of the squall line in western Chongqing. The atmospheric environment in western Chongqing was conducive to the formation of the squall line. There was dry air in the middle troposphere, large vertical temperature lapse rate in the lower and middle troposphere layers, significant CAPE, and large deep vertical wind shear. The formation process of the squall line observed by radar was characterized by the combined development of linear convection with the cold shear line and strong rainfall convection in the southwest vortex frontogenesis region, forming the “herringbone” echo in the west of Chongqing. The cold front behind the “herringbone” echo moved southward, and combined with the evaporation and cooling of raindrops in the dry environment behind the front, cooled down the cold area formed by the rainstorm to the cold pool outflow in the boundary layer, promoting the formation of the squall line. The arc shaped squall line maintained for about 1.5 h after its formation. The southward and downward transport of low level horizontal kinetic energy at the rear of the front area and the enhancing of the potential temperature gradient between the surface cold and warm air during the formation of the squall line all contributed to the formation of the surface gales.