Abstract: Based on data from the Local Analysis and Prediction System(LAPS),as well as observations from satellite,radar,GPS,and automatic meteorological stations,characteristics of a mesoscale convective system(MCS)were comparatively analyzed during two heavy rainstorms in the northeast region of Hubei province on July 12-13,2012.The results indicate that forcing mechanisms of the two heavy rainstorms are distinctly different.One is forced by warm advection due to thermodynamic factors and the other is forced by the front due to dynamic factors.For the first heavy rainstorm,convective cloud has an asymmetric structure.Intensive echoes extend to the high altitudes.Its strong precipitation mainly locates in the areas with great gradients of TBB(Temperature of Black Body)accompanying with thunder and lightning.While for the second one,convective cloud has a symmetric structure.Intensive echoes only reach the lower altitudes.Its heavy precipitation mainly occurs in the center with a large-TBB value,indicating warm cloud precipitation.Two heavy rainstorms last for a long period of time.One reason is that the cold outflows from cool pool in the boundary layer converge with the southerly inflows in the rear of convective system and form a backward propagation that offsets the movement of heavy rain cells,which favors the maintenance of convective systems.The other one is that the convection system moves to the same direction with the steering flows.Heavy rain cells pass the same place successively,resulting in a strong cumulative precipitation.