Numerical Simulation Analysis on the Generation and Evolution of the Dynamic and Thermodynamic Processes of an Extreme Rainfall in Jilin Province

The analysis of circulation background and trigger mechanism of an extreme precipitation weather process was carried out in the Jilin area on July 13−14, 2017 using the ERA-Interim reanalysis data, conventional meteorological observation data, CMORPH (CPC MORPHing technique) fusion precipitation data, and high-resolution numerical simulation results of WRF (Weather Research and Forecasting). The observed results are as follows: (1) The large-scale circulation background of precipitation was found in the northward movement of the subtropical high- and cold vortex over Northeast China and mid-latitude front zone. Precipitation occurred between the bottom of the cold vortex and the subtropical high in the straight zonal circulation. Clod trough, low-level shear line, upper-level jet stream, and low-level jet stream are all critical weather systems that influence precipitation. (2) Extreme water vapor transport, blocking, and forced uplift of the low west and east high terrain in the Jilin area are the factors that cause extreme precipitation in the context of high-level divergence and low-level convergence. (3) Dry and cold air intruded into the middle and upper levels, and high-level momentum was transmitted to the low altitude. Thus, the low-level jet was strengthened, which generated an ultra-low-level jet near the surface, enhancing the vertical ascent movement. The intersection of north-south meridional momentum transport strengthened low-level wind convergence shear. The development of convection along the shear line and the uplift of nearby small terrain led to extreme precipitation in Yongji County.