Abstract:Based on the routine observation data and the Doppler weather radar data, the large scale hail in the northwest of Guangxi is analyzed. The results show that: (1) The systems csusing hail are upper airvortex and low level shear line. Although the CAPE was moderate before the hail, it has necessary conditions for the severe convection potential occurrence such as the stratification of upper dry and lower wet, strong environmental wind shear and the strong clockwise curvature at low levels. (2) The low level reflectivity on the right front of the supercell shows a typical hook echo and it is a typical feature of supercells. Along the inflow direction and through the strongest echo, the reflectivity shows typical BWER (Boundary Weak Echo Region), overhang echo and echo wall. The strongest echo is within a vertical narrow region along the echo wall and can be more than 65 dBz. The corresponding radial velocity in the lower atmosphere has a moderate meso scale vortex street and its rotation speed can be 22 m·s-1. Meanwhile the VIL exceeds 70 kg·m-2 and its density exceeds 5 g·m-3. (3) The positive vorticity at upper levels, high CAPE value, convergence line on the ground stranding in the Youjiang Valley and the special terrain are the main causes for many convection cells moving along similar paths.