分析了2010年5月21日长沙地区大暴雨天气过程的形势,应用NECP资料分析该过程中水汽条件、热力不稳定、上升运动、动力条件等,同时对EC中低层风场、T639物理量、RJ降水预报进行了检验.结果表明,西太平洋副高在华南及沿海发生震荡,高空低槽、中低层西南低涡切变、地面倒槽与气旋波等共同活动,是形成大暴雨的主要原因.中层低空西南急流活动与暴雨有很好的对应关系;暴雨发生在有利的湿度条件下,充足的水汽输送和水汽辐合保证了暴雨所需的水汽条件.由于低层冷空气的嵌入,水汽通量和水汽通量的辐合区有随时间由低层各自往高层发展的趋势；深厚的弱散合层,有利于形成大暴雨.EC各时次风场预报对急流、低涡切变预报较好,预报有强降水理由充足；T639垂直运动预报与实况吻合不好,而水汽通量与实况吻合性好；日本降水预报强度与落区有指示意义.%By using NCEP reanalysis data, an extremely heavy rainstorm process occurred in Changsha on May 21, 2010 was made, which contain the analysis of vapor condition, unstable condition of thermal, ascending motion, dynamical condition etc. And the test of medium-low layer wind field, physical quantities of T639, precipitation forecast of RJ model. The study results show that the main causes that forming heavy rainfall is the oscillation of West Pacific Subtropical High( WPSH) occurred in South China and South China Sea and the collective activity of high trough, southwest vortex shear in medium-low level, surface inverted trough and cyclonic wave. The low southwest jet lying on medium layer is well corresponding to heavy rainfall. The good moisture condition including enough moisture transportation and moisture convergence condition reflect on heavy rainfall. With embedding of cold air, the water vapor flux and its divergence have a development trend from low level to high level. The profound mixed-level of infirm divergence and thin convergence is used to forming rainstorm. The forecast of EC real-time wind field, jet and low vortex shear is relatively exact. It is just that forecast heavy precipitation. The vertical motion forecast is inaccurate, but moisture flux is in good accordance with real. The RJ model is a good forecast index in the rainfall area and intensity.
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