Abstract:

Using Liaoning province automatic station observational data, upper-air observation data, Doppler Radar data, and ECMWF reanalysis data, weather characteristics and predictability of the urban local short-term heavy rain process were analyzed under the background of cold vortex weather in Shenyang on June 30, 2016.The results show that the weather process is a typical afternoon strong convective weather.During the day, solar radiation heating results in the urban temperature higher than the surrounding areas and there is significant unstable energy in the middle and low-level with a high humidity environment.Southwest airflows from the ground to 300 hPa height have increased continuously since 2 hours before the rainstorm, meanwhile, the exit area of the low-level jet is depressurized, leading to intensifying the vertical movement and the ascending movement reaching the tropopause, which is beneficial to trigger and strengthen convection.Southwesterly wind pulsation and the weakening and disappearance of jets at heights from 1.5 km to 3.0 km and with the speed of 16 m·s^-1 have a good indication of the occurrence and end of precipitation.The unstable stratification resulting from low-level convergence and high-level divergence in the afternoon is also established 2 hours before the heavy precipitation, and the maximum divergence corresponds well to the heavy precipitation.Radar observations indicate that the precipitation is dominated by low-centroid warm clouds with high precipitation efficiency.The surface convergence line triggers convection, which gradually develops into a belt-shaped convective system.Judging from the results of the numerical forecast, the model failed to report the impact of the city's underlying surface on meteorological elements, and the forecasting surface convergence line was lagging and weak, leading to the forecasting difficulties of heavy precipitation.

Key words: Heavy precipitation, Urban underlying surface, Surface convergence line, Predictability