Abstract: Based on the conventionally observational data, meteorological data from automatic weather stations and Doppler radar data and so on, a rainstorm and locally heavy rainstorm event on July 14, 2009 in Dalian area were analyzed. The results show that it is a warm front rainstorm process. The upper-level trough located in Hetao area moves northward and overlays with the tail of the north branch trough. In the middle and low levels, a vortex circulation forms from the northern Bohai Sea to Dalian area. The region of high cyclonic curvature at 700 hPa is located above surface warm front. The top of surface cyclone, i.e. the top of warm front is just in Dalian area. This weather pattern results in the occurrence of heavy precipitation. High humidity area together with low-level convergence centre in front of the warm front and upper-level divergence centre provides favorable moisture and dynamic conditions for heavy rainstorm event. Radar echo analysis shows theβ-middle scale reflectivity area with 45 dBz in front of the warm front and the “single oxeye” characteristics in radial velocity field directly contribute to this rainstorm and short-time strong precipitation. The analysis of VWP data shows the height of shear layer formed by low-level southeasterly jet and upper-level southwesterly jet and the intensity variation of the two jets correspond to warm front and determine the rainfall intensity.

Key words: Rainstorm, Velocity image, Warm front, Single oxeye feature, VWP data