Based on conventional sounding observation data, ground encryption observation data and EC-interim reanalysis data with high resolution (0.25°×0.25°), the rainstorm process in northern and central part of Shaanxi Province during August 21-22, 2018 was comprehensively analyzed. The precipitation forecast based on the model was tested, and comparison of circulation conditions, water vapor conditions, energy conditions and instability mechanism of the heavy rainfall in the northern Shaanxi and the western part of the Guanzhong plain was focused on. The results show that cold air brought by the plateau trough and warm air brought by the subtropical high met in the central part of Shaanxi, which provided a favorable circulation background for the heavy rainfall. The shear line on 700 hPa provided a dynamic uplift condition for rainfall. The northwest cold front in the Hexi Corridor moved southward. The stable precipitation behind the cold front dominated in  the northern Shaanxi, while the convective precipitation triggered by the cold front dominated in Guanzhong area. During the rainstorm, the water vapor transport was weak, the local water vapor content was high, and the vertical gradient of humidity in western part of the Guanzhong plain was large, which was conducive to enhancement of convection and increase of rainfall intensity. Before the rainstorm, there were obvious convective instability in the middle and lower layers in western and central part of the Guanzhong plain and the convective effective potential energy (CAPE) was larger. Weak cold air triggered release of unstable energy in the Guanzhong plain and produced further convective rainstorm. However, there was a neutral stratification with weak unstable energy in northern Shaanxi. Conditionally symmetrical instability in the middle and lower layers resulted in strong oblique updraft, heavy rain and rainstorm. The frontogenesis of cold and warm air intersection in the Guanzhong plain was the triggering mechanism of convective rainstorm in this area. For large-scale precipitation, the forecast based on the model was stronger, but for convective precipitation, the  forecast  based on the model was weaker.

The NCEP 1° × 1° reanalysis data，FY － 2E satellite images，conventional meteorological data，and the method of combining satellite cloud images with atmospheric dynamic field were used to analyze the dry intrusion characteristics under the influence of cold eddy and the role of the dry intrusion during the short － time strong rainfall which occurred in Yulin of Shaanxi Province on July 15， 2012． The results show that the characteristics of the dry intrusion was significant during the short － time strong rainfall process，the high value area of TBB on satellite water vapor images corresponded to the dry cold area of upper troposphere，while the stretching of the cold dry area made the TBB gradient on convective cloud edge increase，at the same time convective cloud developed． The dry intrusion corresponded to the sinking motion，high value area of potential vorticity and dry cold areas in the upper troposphere，the instability stratification appeared over the heavy rainfall region due to the dry cold air overlaying the warm wet air，which created favorable environmental conditions for the occurrence of the short － term heavy rainfall． In addition，water vapor of the rainfall process mainly concentrated in the lower troposphere，short － term moisture convergence caused by wind convergence created a favorable moisture condition for the short － term heavy rainfall． The lifting of air mass that contained water vapor caused by the trigger mechanism of mesoscale convergence line on the ground led to precipitation．

different level rainy days and its homologous precipitation quantity are obtained by using the daily precipitation data from
May to September ( 1960 － 2004) of 17 stations in the Qilian Mountain area，thus，we know the daily precipitation intensity of light
rainfall and moderate rainfall( and more) at each station． Based on regional mean value of the different level rainy days and rainfall intensity
in Qilian Mountain area，the tendency of the different level rainy days and rainfall intensity was analyzed using linear trend coefficient
and 5 levels main value function． The results show that both precipitation and different level rainy days from May to September
in Qilian Mountain area presented more in the west side and less in the east side in the same latitude area，and more in the east and
less in the west part of Qilian Mountain． In recent 45 years，the light rainfall days was descending，but the moderate rainfall days was
ascending． The precipitation intensity of light rainfall and moderate rainfall ( and more) presented ascending trend too from May to September
in Qilian Mountain area． The morlet wave analysis show that the light rainfall days had a period of five years，but the period of the moderate rainfall ( and more) days was more complex．

The heavy rain process occurred on July 15 in 2003 in Ningqiang of Shaanxi province was analyzed. Results show that the meso-α-scale convective cloud cluster resulting in this heavy rain were elliptic or round and lasted for 17 hours, and the contribution of vapor convergence at the level of 850 hPa was more important than that of southwest jet on 700 hPa to the heavy rain, and the continuous and powerful updraft supplied by the jet sub-circulation was main cause for maintaining of the meso-α-scale convective cloud cluster.