Analysis on the Cause and Forecast Deviation of an Extreme Rainstorm in Changsha Urban Area

Using NCEP reanalysis data,high-altitude and ground observation data,numerical model data,satellite and radar data,formation cause and forecast deviation of an extreme rainstorm process in Changsha urban area at night on June 9,2020 were analyzed.The results showed that(1)the extreme rainstorm process developed near the surface convergence line,with strong localization,short duration and large hourly rainfall intensity.(2)Under the high temperature and high humidity environment,the low-level cold advection and the hot low-pressure system interacted,and the potential con-vective unstable energy was released,and a strong convective weather was formed.(3)The convergence of water vapor in the lower layer and the strong upward movement provided sufficient water vapor for the rainstorm.The low-centroid thunderstorm was the main reason for the extreme rainstorm.(4)The forecast deviation of the numerical model to the low-level shear line and the mesoscale convergence line was an important reason for the forecast deviation of the heavy rainfall area.