Abstract: The radar features and environmental background during a regional severe thunderstorm on June 5,2014 in Guangxi Zhuang Autonomous Region were investigated using methods of a synoptic meteorology and a diagnostic analysis with conventional meteorological data,observations from regional automatic weather stations and Doppler radar,as well as the NCEP reanalysis data with resolution of 1.0°×1.0ånd 2.5°×2.5°.The results indicate that the severe thunderstorm is caused by two bow echoes according to the radar detection.The forward-tilting trough at 500 hPa and quasi-stationary front at the surface provide favorable conditions for the formation of the thunderstorms.The intensity of the bow echo in the northern Guangxi Zhuang Autonomous Region is weak and it moves slowly,with a low barycenter and vertical upward structure,which causes repeatedly short-time heavy rainfall and ultimately leads to a large-scale rainstorm.However,the intensity of the bow echo in the southern Guangxi Zhuang Autonomous Region is relatively stronger and it moves faster,with typical characteristics of thunderstorm gale,such as front and rear inflows,inclined structure and mid-altitude radial convergence (MARC).This bow echo causes the regional gale and local short-time heavy rainfall.Mid-level humidity and vertical wind shear are background reasons for the different weather types in the northern and southern Guangxi Zhuang Autonomous Region,respectively.The dry air,controlled by the subtropical high,moves to the north along southwesterly jet,and makes dry air advection over the southern Guangxi Zhuang Autonomous Region.The 500 hPa trough moves rapidly toward the area of the subtropical high,which leads to a greater pressure gradient and generates southwesterly jet between 850 and 500 hPa as well as strong vertical wind shear.

Key words: Thunderstorm feature, Bow echo, Mid-level dry air area, Vertical wind shear