| Based upon observational data and satellite images, feature analysis of the regional rainstorm occurring in July 18-19, 2007 in Shandong is made firstly. Secondly, a primary diagnostic analysis of the heavy rain has been done from water vapor, dynamical to thermal conditions by using NCEPl°xl°re-analysis data. Finally ,the Regional Atmospheric Modeling System RAMS6.0 is also used to simulate the heavy rain; then the process and the mechanism of the rainfall are analyzed in more detail.Fact analysis showed that: the main influenced systems are Northeast Vortex, Westerly trough, horse latitude high, Southwest Vortex, the upper level jet and low level jet. The Hetao wave trough development caused the cold air moved south ward, and the low level jet in Southwest Vortex development and horse latitude high development carrying warm and moist air provided for an enabling environment for the rainstorm. The structure of the forward-titled trough increases the atmospheric instability and may one mechanism of causing the severe convective weather.Numerical simulations results show that: (1) The appearance of circulation in the low level and the coupling of the upper level and low level are the main reason of the heavy rainfall of Jinan. (2)The distribution evolves of PV had the good corresponding relations with the precipitation process, the PV carries over forecasts strongly the direction of the fall, the PV increase is corresponding the strong precipitation increase. the upper air cold air invasion diagnosed by PV also is one of convection development triggering mechanisms.The diagnosis of vertical helicity turns out that the vertical helicity level distribution has the very good corresponding relations to the precipitation distribution, honorable value center between 700hPa and the 500hPa corresponds the strong precipitation center, the helicity center intensity is increasing suddenly and reduces has the very good instruction significance to the precipitation appearance and the conclusion.
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