Abstract:Guangxi encountered a double convective bands process from 20:00 BT 25 March to 08:00 BT 26 March 2023, which are significantly different from that of the double traditional rain belts, resulting in a significant deviation in the subjective forecast. Based on multi-source observation data and ERA5 reanalysis data, the Rossby wave energy dispersion, moist potential vorticity and horizontal frontogenic forcing were diagnosis and analyzed in this process. The results show that the process occurred under the background of large-scale circulation adjustment. The two Rossby wave trains originated from the polar vortex and the Black Sea in the middle and high-latitude jointly promoted the gradual vertical rotation of the northeast transversal trough, and guided the mid and high latitude cold air further southward. During this period, the south branch trough in the low latitude gradually moved eastward, which provided the dynamic lifting above the cold cushion in Guangxi, and also promoted the convergence of cold and warm air in the low level in Guangxi. With the addition of cold air to the south and southerly winds advance northward under the inertial oscillation, the convergence of warm and cold air in Guangxi was enhanced, and the enhancement of atmospheric moist baroclinicity leads to the development of moist potential vorticity, resulting in conditional symmetric instability of stratification. Warm and moist air climbed from south to north to the conditional symmetric instability area near 700 hPa, and then combined with the positive vorticity advection in front of the upper level trough to trigger elevated convection, resulting in the development of the northern branch convective band. Influenced by the special topography of Guangxi, the favorable configuration of the θse isoline and the flow formed a tensile deformation effect, resulting in frontogenic forcing, which triggered the initial convection in the south branch of Northeast Vietnam. The large θse latitudinal gradient and strong vertical wind shear in the low level of the central Beibu Gulf resulted in strong moist baroclinicity, which promoted the organization development of the southern branch convective system when it passed through, and formed bow echo due to the mid-level dry air ensnagging.