Abstract: Lower-middle-level wind data between 0.5 and 5.0 km retrieved using the Doppler radar data 4DVAR,as well as observation data from ground-level,upper-air and regional automatic weather station (AWS) were used to comprehensively analyze the formation and development of the windstorm during a disaster-causing severe convective process occurring on June 8,2016 over Qinhuangdao.The impending early-warning on multi-cell windstorm was discussed as well.The results show that the stratification conditions with cold and dry air at upper levels and wet and warm air at lower levels favor the formation of severe convective weather.The trigger mechanisms of the process were ground-level convergence lines and dew point fronts,and the sudden changes of wind and temperature data from AWS had a good implication for determining the gust front of the storm cell.When the storm cell strengthens into a supercell and is near to the gust fronts,convergence ascending motions caused by outflow and inflow are mainly located on the edge of the regions where the echo intensities are 15-30 dBz between lower and middle levels in the supercell.Downward airflows always appear in relatively strong echo regions at lower levels,whereas the separations of the ascending and descending motions ensure the long-time development and propagation of the supercell.When the outflow gust fronts are far away from the back of the mature storm,a new convective storm is triggered to form at a distance of about 15.0-20.0 km,leading to the backward propagation of the convective system.Through the estimations on the propagation vector motion directions,one can find out the development regions of the windstorm in advance,with the early-warning time of 30 min.Persistent values of vertically integrated liquid density (VILd)above 4 g·m^-3 are important indicators for the forecast of large hails with the sizes of 2-5 cm.

Key words: 4DVAR, Supercell, Gust front, Backward propagation, VILd (vertically integrated ligqid density)