Synthetic discussion on the causes of the first severe convective weather causing disaster over Hunan in 2013

Using data from various radars in Hunan and radiosonde data, meso-and micro-scale observations of automatic weather stations,meteorological records at the Nanyue Mountain station and LAPS data, this paper analyzes the causes of the first severe convective weather process causing disaster over Hunan on 19 March 2013, and then explores the early warning focus and predictability for strong hail and thunderstormgale. The results show that before the process, intense warming near the ground by sky radiation, instable convection stratification,strong vertical wind shear, strong temperature gradient lapse rate and abundant water vapor near the ground provide good potential conditions for the occurrence and development of the severe convective storm. All the factors including cold advection in the mid- and low-level, surface mesoscale convergence line, energy front and dew point front as well as the dynamical coupling of weak divergence near the ground, strong convergence in the mid- and low-level and divergence in the upper level form the main trigger mechanism of the severe convection. The prophaseof this severe convective storm is characterized by supercell storms and multi-cell storms. While moving eastwards and jumping northwards,the supercell storm combines with convective echo generating continuously in western Hunan and develops into a squall line; at the same time, while the maintenance and development of squall line, bow-shaped echo, middle-level radial convergence, low-level divergence and great value zone of velocity are seen in the radar chart. In the nowcasting services, the obvious hook-shaped echo structure in the mid and low-level, continued high reflectivity factor and vertical integrated liquid (VIL) provide an effective basis for the early warning issue of heavy hail in Jingzhou, but the great value zone of radial velocity (>20 m·s-1) at low angle (within 1 km from the surface) provides important reference for the early warning issue of thunderstorm gale in Daoxian.