Abstract:By employing the NCEP/NCAR reanalysis data and routine observation data, the causes of heavy rainfall in Weihai on 19 and on 24 July 2008 are analyzed. It is shown that the establishment and the maintenance of the blocking anticyclone over Northern Asia lead to the southward movement of the westerly frontal zone and the dry cold air. The changes of the general circulation enhance the torrential rain over Weihai. The rainstorm processes are the result of the joint action of the high-level cold vortex and the low-level shear line or low pressure. It is also revealed that once the dry cold air meets the moist warm air over Shandong Peninsula, the heavy rainfall develops. The vapor comes from the East Sea and Yellow Sea. The vapor convergence comes into existence in Shandong Peninsula and plays a crucial role in the maintenance of the strong precipitation. In the period of rainstorms, the convergence in the underlying bed and the divergence in a high-level are characteristic of a divergence distribution. The convective ascending movement and the strong updraft found over 800 hPa and below 400 hPa provide a favorable dynamic condition for the rainstorms. The sufficient high energy of the potential pseudo-equivalent temperature θse in the rainfall region, the energy frontal zone in the northwest of the high energy area and the moisture provide the thermal condition for the formation of heavy rainfall.