Genesis of Successive Quasi-Linear Convective Systems over North China: Dynamical and Thermodynamic Forcing by a Cold Vortex, Complex Terrain, and Surface Boundaries

Quasi-linear convective systems (QLCSs) frequently produce severe weather in North China, with multiple QLCSs often forming successively within a short period. However, their formation mechanisms under such conditions remain unclear. This study investigated the formation mechanisms of three successive QLCSs that affected Beijing and its vicinity from the afternoon to evening on 12 June 2022, using in-situ and remote sensing observations as well as high-resolution Weather Research and Forecasting model simulations with a 9-, 3-, 1-km nested grid. The event occurred within the trough of a mature cold vortex, which induced dry westerlies over the western mountainous areas and moist southerlies over the eastern plains of North China. Diurnal solar heating further intensified the zonal thermal and moisture contrasts between the eastern and western domains. Therefore, a southwest–northeast-oriented dryline with a dynamical confluence persisted along the eastern Taihang Mountains. To the west of the dryline, sustained boundary layer turbulent activities eliminated convective inhibition. Meanwhile, episodic weak cold advections induced by the cold vortex modestly increased the convective available potential energy over the northern mountains, providing energy for the generation of convective cell clusters (CCs). These sequentially initiated CCs propagated southeastward under the steering airflow, with distinct outflow boundaries forming at their leading edges. Crucially, the continuous merging between the southeastward-moving CC outflow boundaries and the quasi-stationary dryline strengthened the low-level convergence both in depth and intensity along segments of the dryline zone. The intensified dynamical lifting ultimately triggered convection along these segments, corresponding to the successive formation of three QLCSs. This paper highlights the synergistic effects of cold-vortex forcing, complex-terrain modulation, and dryline–outflow boundary interactions on the formation of organized convection over mountainous areas. The findings benefit the forecasting and early warning of similar severe convective events in North China.