Synthetic discussion on the causes and early-warnings of the first wind-hail strong convection weather over Hunan in 2018

Based on the conventionally observed data, NCEP 6 hourly reanalyzed data, FY-2G satellite TBB data and Doppler weather radar data, we analyze the causes of the first wind-hail strong convection weather process over Hunan on 4 March 2018, and then explore the early warning focus and predictability for strong hail and thunderstorm gale. The results show:1) The process of wind-hail is divided into two stages, i.e., the "low-level warm advection forced" and the "baroclinic frontogenesis". In the "low-level warm advection forced" stage, under the southwest warm and humid flow, wind-hail weather is triggered by the ground mesoscale convergence line and consists of stratified mixed precipitation echoes which is moving to northeast. Line-storm has developed in front of echoes. In the "baroclinic frontogenesis" stage, the radar echo is triggered by cold front and consists of accumulated clouds, moving to southeast. Multiple supercell storms occur at this stage. 2) The apparently low SI and high CAPE, DCAPE, and vertical wind shear make the windy weather extreme. Comparing the two stages, in the first one the range of DCAPE is wider and strength is stronger, and dry layer in the middle layer is obvious, which tends to the emergence of thunderstorm gales. In the second stage, vapor and dynamic factors are stronger and more concentrated in southern Hunan. With the cold front moving, the height of 0℃ and -20℃ isotherms are decreased, which is beneficial to the occurrence of hail. 3) The large radial velocity at low elevation, MVT and sustaining mesocyclone are the key points for early-warning of thunderstorms.