Abstract:The capacity of global model in forecasting of warm sector heavy rainfall is still very limited at present, especially for warm sector rainfall in northern China, which is one of the most difficult problems in operational forecasting. A severe regional torrential rainfall case which consisted of both warm sector and frontal precipitation attacked Hebei Province and Tianjin during 1-2 July 2013. As for the severe rainstorm ［409 mm·(24 h)-1］ in the middle part of Hebei Province, the ratio of warm sector rainfall accounted for more than 60% of total precipitation. The heavy rainfall of this event was seriously underestimated in the subjective quantitative precipitation forecast in NMC (National Meteorological Centre) with obvious missing forecast on rainstorm and severe rainstorm. Moreover, none of the numerical weather prediction (NWP) models can provide enough useful information to weather forecasters, which further increased the forecasting difficulty and caused the failure of QPF (quantitative precipitation forecast). In this paper, operational numerical model forecast products, automatic weather station observation, conventional surface and radiosonde observation, and Doppler radar data are employed to investigate the cause of the failure forecast of this warm sector torrential rainfall case. The results show that failure of capturing the sub synoptic and mesoscale small disturbances, such as surface convergence line, gust front, cold pool, and mesoscale vortex, as well as their effects on heavy rainfall under a high temperature and high humidity conditions was one of the important factors leading to the underestimation of the rainfall intensity. Furthermore, insufficient fine analysis on the environment condition in triggering mesoscale convection systems like low level jet and the evolution of jet core also played important roles. Therefore, in terms of forecasting the warm sector rainfall within a very thick warm wet air mass, the triggering caused by interaction of surface convergence line, cold pool and mesoscale vortex and organizational development of local and convective precipitation in the high temperature and high humidity environment must be considered. Short time forecast and nowcasting based on surface automatic weather station observation and weather radar data could effectively compensate the lack of ability in finding mesoscale and small scale systems by global NWP models, which may improve the accuracy of forecasting warm sector rainfalls.