[Objective] The aim was to discuss the heavy rainfall formation mechanism and to reveal the causes of rainstorm. [Method] Based on the conventional observational data, a numerical simulation and diagnosis analyses have been carried on heavy rainfall event over Jiangxi province from 16 June to 20 June 2010, with a meso-scale REM model. The results showed that this rare rainstorm was a typical heavy rainfall over Meiyu front. The cold air flow behind the 500 hPa East Asia trough and 700 hPa North China vortex joined up the southwestern flow located in the northwest part of the strong and stable subtropical high, thus the cold air and warm air converged and maintained over the northern part of Hunan and Jiangxi province. Since the area that cold air and warm air joined up was stable and the southwestern warm and wet flow was abnormally strong, the vapor, dynamical, and thermodynamic conditions was leading to the trigger development of meso-scale convection systems. The extraordinary rainstorm was caused by the interaction of many factors such as strong vapor and convergence ascending motion, weak cold air activities in middle-levels, the strengthening of southwestern low-level jet, the formation and maintenance of southwestern vortexes, etc. The simulated precipitation of the high resolution model was very similar with the observational rainfall. The model had a good predictive skill for the location, intensity and center of heavy rainfall. By diagnosing the physical variables, it found that the distribution characteristic of the physical variables had an obvious indication for precipitation forecast. [Conclusion] The study provided reference to improve rainstorm forecast.
