Analysis on Mesoscale Mechanism of Heavy Rainstorm in Jinan on 18 July 2007

Mesoscale mechanism of the formation of heavy rainstorm in Jinan on 18 July 2007 was studied using the conventional observation data,unconventional observation data,the averaged fields of GFS(Global Forecast System) 0.5°×0.5° analysis data and WRF(Weather Research and Forecasting model) simulation results.The results show that the low-level jet,cold air reflux from Inner Mongolia and dry air on the middle level of the troposphere form the favorable environment to the mesoscale convective system.In addition,mesoscale convective systems develope on the mesoscale convergence line on the westsouth side of low vortex.In mesoscale vortex entering into the sea process,its moving speed is to decelerate,which result in the slowdown of velocity the convergence line passing Jinan,which lead to 3 h heavy rainstorm there.It is convective cells generated ahead of the gust front at distances about 30 km combining with the MCS that contributes to the excessive precipitation.