A heavy rain occurred in the eastern edge of Tibetan Plateau during August 25 － 26 of 2007 resulted in serious disaster． The
weather system and vapour transportation was analyzed by using NCEP( 1° × 1°) data，and then the PV theory was used to study the
mechanism of the heavy rain． The results show that the strong vapour transportation in the edge of the subtropical high and vapour convergence
over the rainstorm area was the important reason for the rainstorm occurrence． The strong instability before the rainstorm provided
benefit thermal condition． The northwest cold low trough had not obvious sign on the pressure field in the course of the rainstorm，
which only formed a weak wind shear near the rainstorm area，and it had small effect on this heavy rain． But the 325 K isentropic surface
had obvious indicating meaning for the rainstorm occurrence，when the cold air with higher PV value slided down to the low level
along the steep isentropic surface，the vertical vorticity increased rapidly because of the conservation of PV，as a result，the heavy rain occurred．

The app lication of K drought index for droughtmonitor operation in Gansu was introduced in this paper, and the mainly analysiswas as follows: the definition, grades, criterion, app lication of K drought index, and the comparison between monitor results of K drought index and actual drought situation. Results indicate that there is a good effect in droughtmonitorwith K index compared to actual drought situation in sp ring, May, June, July to August, and Sep tember in 2008 in Gansu p rovince.

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.