A Snowstorm occurred on October 18, 2002 in the northeast side of the Qinghai - Xizang Plateau was analyzed by using the
global re - analysis data (1°×1°) ofNCEP. The results show that the p lateau’s shear line generated by the combination of the south2
west warm moist currentmoving northward at 500 hPa and the northwest cold airmoving to east and west in the region near 36°N resul2
ted in this weather event. This snowstorm occurred in an intensive belt of positiveMPV1 at 700 hPa and a negative area ofMPV2. The
increase of the absolute value ofMPV2 and atmospheric moist baroclinicity with the atmospheric convective unstable energy releasing,
and the down - sliding slantwise vorticity developmentwere the important reason for the formation of the snowstorm. It has a good indic2
ative effect for the snowstorm forecast.

This paper analyzed the synop tic system such as the high and low jet, the frontwhich induced the regional rainstorm in the middle - east part of Gansu p rovince during 28 - 29May 2004 by usingMicap s and ECWMF data. Results are as follows: (1) The cold air and the shortwave trough disrup ted from the westly jet at the level of 500 hPa which moved from the UralMountain to the Balkhash Lake, moved along the bottom of the jet to the Hexi Corridor of Gansu and the middle part of Qinghai, which p rovided energy for the rainstorm; (2) The SW flow at the edge of subtrop ical high p rovided abundant vapour for it when subtrop ical high withdrew rap idly eastward and southward; (3) The vertical velocity, the vapor flux and the divergence of vapor flux have good indication to this rainstorm, and the total temperature advection and the differential advection have important contribution to the rainstorm.