A heavy rainfall process in Guangdong Province on 17-18 in June of 2009 was simulated by the mesoscale numerical model MM5 and was analyzed with the synoptic charts and satellite imagine.The results indicated that 500 hPa southern trough and 850 hPa shear line constituted the two systems of causing the weather process of heavy precipitation,whose favorable configuration was the focus of the heavy rain forecast.High-level westerly jet stream played an important role in this heavy rainfall process.With the 'suction effect' of strong upper-level jet divergence at 200 hPa level,the low-level shear line pressed southward,which made low-level warm damp air move upwards along the shear line so as to generate a strong upward motion,providing favorable background conditions for the occurrence and development of heavy precipitation.There was fairly good correspondence between 850 hPa horizontal helicity center and the influence system's development and movement.The distribution of horizontal helicity had a certain relationship with the falling areas of heavy precipitation.
