Abstract:Based on Jinan Doppler weather radar data, sounding and automatic weather station data, the radar echo characteristics including the effect of cloudstreets on three heavy rainfalls in Shandong Province were analyzed. The results showed as follows. The cloudstreets appear as narrowband echoes oriented in the direction of mean low level wind in low level base reflectivity, the duration is about 6-7 hours, and the intensity is about 5-20 dBz. The main effects of cloudstreets on three heavy precipitations are as follows. First is the triggering mechanism. Cloudstreets can trigger convection cells. Second is the backward propagation mechanism. The new storms triggered by cloudstreets spread to the southwest in turn along the orientation of cloudstreets. This backward propagation characteristic can lead the convective system to move toward west by south direction and lead the severe precipitation area to the southwest direction. Third is enhancing precipitation intensity and duration. The continuous storms triggered by cloudstreets develop northeastward under the action of the pilot airflow, and merge with the main echoes of convective system. Therefore, the main echoes will be strengthened, generating large rain intensity and lasting for a long time, finally resulting in extreme severe rainfall weather. The cloudstreets play an important role in the maintenance and development of the three convective systems and in the generation of extreme severe rainfall. The frequency of thunderstorm triggered in the 18 July process is significantly higher than that of the other two processes, and the main reason is that the convective inhibition energy (CIN) is significantly smaller than the other two processes. Small CIN and lifting condensation level are easier to trigger the outbreak of thunderstorms.