Using conventional observations, satellite and radar observations, and ERA5 reanalysis data, this study analyzed the heavy precipitation characteristics, environmental conditions, and mesoscale system evolution associated with the localized extreme torrential rainfall event in the western Sichuan Basin on 11 July 2023. Furthermore, through analyses of orographic lifting velocity, mesoscale dynamical diagnostics, and latent heating effects, it explored the possible physical mechanisms responsible for convective initiation, organization, and maintenance. This rainstorm was a warm-sector event on the plateau slope under weak large-scale synoptic forcing, caused by a meso-β-scale convective system originating from a multi-cell linear storm. It differs from large-scale basin-wide rainstorms driven by significant synoptic-scale forcing. The precipitation featured a narrow, quasi-stationary band with a notable train echo effect. Short-duration heavy rainfall lasted for 8-9 hours, with a maximum hourly rainfall intensity of 83.7 mm·h-1 and a 12 h accumulated rainfall of 371.9 mm. Heavy precipitation was concentrated in the canyon terrain and steep windward slopes of the northern Longmen Mountain, highlighting the prominent role of topography. After nightfall, mountain breezes accumulated at the valley bottom, forming a cold pool. The warm and moist southeasterly flow within the boundary layer rides up over this cold pool, initially triggering localized weak convection.At midnight, the establishment of the southeasterly low-level jet enhances the orographically forced lifting rate on the windward slopes, resulting in intensified convection. Simultaneously, influenced by topographic blocking, a northeasterly diverted flow develops in front of the mountains, forming a shear line with the ambient southeasterly wind, which facilitates the organized development of convection along the terrain. On the other hand, the nocturnal thermal contrast between the plateau and the basin generates a pronounced horizontal temperature gradient that reinforces the low-level vertical wind shear in the piedmont region. That is, the orographic thermal forcing favors the acceleration of the boundary-layer southeasterly flow in the foothill area, thereby further promoting the organized development of convection. The synergy of three processes—a positive feedback between convective latent heat release and vorticity development that enhanced upward motion, cold/warm advection at upper/lower levels that amplified instability, and continuous moisture supply by the southeasterly.