Abstract:Based on the dense observation data, NCEP reanalysis and infrared TBB data, the system features and the cause for the rainstorm process on the east side of Ailao Mountain on 15 June 2012 have been diagnostically analyzed. The results show that the shear line at 700 hPa becomes the shear line parallel to Ailao Mountain after it moves to the mountain because of Yunnan Burma ridge and terrain. The surface cold front becomes stationary front after it moves to the east side of Ailao Mountain. At the same time, surface cold air is supplied from north, cold air sinks and warm air increases, so strong ascending motion takes place. The mesoscale convective cloud cluster that forms in the convergent cloud belt near the shear line produces “train effect”, guided by the northwest flow and results in convective rainstorm. The vapor from East China Sea and Bay of Bengal converges at the nearby shear line. Deep moisture convergence layer caused by wind convergence nearby Ailao Mountain is main vapor characteristic in this sudden rainstorms weather. The hourly surface automatic station sea level pressure field and CAPE have significant changes before the occurrence of sudden rainstorm along Ailao Mountain, severe precipitation primarily happens near mesoscale surface warm depression and high value area of CAPE. These results would be indicative to the forecasting and warning of this type short time severe precipitation.