Based on ground conventional observation data and intensive observation data from automatic weather stations, cloud images of FY-2G satellite, Doppler radar data and ERA5 reanalysis data, the mesoscale synoptic characteristics of a extremely rainstorm process caused by convergence line frontogenesis in eastern and northern Guizhou on 10 May 2021 were analyzed, and the formation mechanism was preliminary discussed. The results show that the extremely rainstorm process occurred under the background of low vortex shear, and the strong southerly wind at low level transported abundant water vapor and unstable energy for the occurrence and development of the mesoscale convective system, the surface convergence line and its frontogenesis provided triggerring condition for the rainstorm. The rainstorm areas mainly occurred in the large gradient areas of temperature black body (TBB), in which were located on the west or south side of the low value center of cloud cluster TBB, and they appeared a strip-shaped distribution in east-west direction along the surface convergence line. The strongest precipitation occurred at the merging stage of convective cloud cluster. The frontogenesis caused by the convergence line frequently triggered convective cells on the west side of the convergence line, and the new convective cells moved and developed eastward along the surface convergence line, which continuously affected the eastern and northern regions of Guizhou Province. At two stages of the strongest precipitation, the warm cloud and overhang structure characteristics of radar echo were obvious. The surface convergence line and its frontogenesis, the cooling and increasing pressure generated by the upstream precipitation and continuously strengthening southerly wind were conducive to the enhancement of water vapor convergence in rainstorm areas. In the vertical direction, the ascending branches of meridional and zonal mesoscale secondary circulation were located near the extremely rainstorm center, which was conducive to the maintenance and enhancement of mesoscale convective system.

By using meteorological observation data from eight weather stations in Southwest Guizhou and Micpas data and NCEP reanalysis data in recent five years， the spatial and temporal distribution of fog weather in Southwest Guizhou was analyzed in this paper． The results show that the main synoptic patterns resulted to fog weather here were the westerly flow in front of the southern trough and the northwest flow behind the upper trough，and physical quantity fields analysis indicated that the low － level air was wet when frontal fog appeared，and the atmosphere structure was relatively stable，there was a temperature inversion layer in lower level，and a weak upward motion nearby frontal area．