It is difficult to forecast heavy precipitation under complex terrain in mountainous areas， which formation mechanism is complicated， and often brings serious geological disasters. Based on conventional observation data， European Centre for MediumRange Weather Forecasts ERA5 reanalysis data， FY-4A satellite cloud imagery， Doppler radar data and forecast products from various models， the factors contributing and model forecasting performance of local short-time heavy precipitation process in the Hanjiang Basin of southern Shaanxi from the night on 3 to the early morning on 4 June 2022 were examined and analyzed. The results are as follows：（1） This process is a short-time heavy precipitation triggered by the front in the Hanjiang Basin of southern Shaanxi. Due to shallow convection instability and weak vertical wind shear， the heavy precipitation exhibited localized characteristics with significant intensity. The accumulated precipitation in 12 hours exceeds 50 mm in many stations， with a maximum of 104. 8 mm. （2） The two ends of the front are blocked by the topography and move slowly and are difficult to cross the high mountains. Consequently， convection is continuously triggered within the basin， generating heavy precipitation， and the secondary circulation formed in the surface layer of the basin can enhance convective activity. （3） A cold pool formed in the front of front continuously triggers the backward propagation of new convective cells within the basin to form a train effect. Meanwhile， the intense radar reflectivity factor， exceeding 50 dBZ， is located below the 0 ℃ isotherm level， which has high precipitation efficiency and prolonged duration， thus bringing a short-time heavy precipitation with a maximum of 62. 6 mm·h-1 . （4） Global models displayed limited capability in forecasting this process， while mesoscale regional models can reflect the characteristics of frontal convection and precipitation， especially CMA-TRAM and CMA-GD models can reflect the triggering and development trend of local strong convection well. However， the intensity and organization of the convective system induced by the frontal cold pool of the front still have substantial forecast deviations.

In order to get a deeper understanding of the water vapor characteristics and sources of rainstorms in semi-arid areas in Northwest China, and improve the ability of rainstorm forecasting in this area, based on upper-air and surface observation data and European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation global atmospheric reanalysis (ERA5) (0.25 × 0.25),the characteristics of water vapor transport and budget of two large-scale rainstorm processes with different intensities occurring in northern Shaanxi under different circulation on July 11 and August 9, 2022 were analyzed. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to quantitatively analyze the source and contribution rate of water vapor. The results show that the high level trough, low level shear line and vortex and low level jet were the main influence systems of the rainstorm occurring on July 11. 700 hPa cyclonic convergence and 850 hPa low vortex strengthened and moved slowly, causing regional rainstorms. The short-wave trough and low-level shear line were the main influence systems of the rainstorm process on August 9, and the secondary circulation on both sides of the shear line lifted the warm and humid air flow outside the West Pacific Subtropical High (referred to as "West Pacific Sub-high") triggering the release of unstable energy and forming a large-scale convective rainstorm weather. On July 11, the vertically integrated water vapor fluxes from ground to 300 hPa was stronger, 700 hPa southwest jet and the 850 hPa southeast jet formed two obvious water vapor transport belts. The strong convergence lasted longer, the wet layer was deep and the weather process was dominated by stable precipitation. On August 9, under the control of subtropical high, the atmosphere over northern Shaanxi had high temperature and humidity, and the total amount of precipitable water was large. The water vapor transport was weak and the strong convergence maintenance time was short, the wet layer was thinner, but the energy was sufficient, the weather process was dominated by convective precipitation. On July 11, the water vapor net income mainly came from the ground to 500 hPa, of which accounted for 52% during 800-500 hPa. The water vapor income of the eastern boundary below 800 hPa increased rapidly during the precipitation intensification stage and the combination of increased zonal income and strong meridional income keeps the regional net income at a high value, resulting in regional heavy rain. On August 9, almost all of the water vapor net income came from meridional income, and the water vapor net income mainly came from the ground to 800 hPa (accounting for 88%). The 700 hPa shear line moving southward and the convergence in the north of Yulin increased, reduced the outflow of the southerly wind, significantly increased the meridional income of water vapor, and strengthens the rainstorm. Water vapor backward trajectories with HYSPLIT model showed that on July 11, water vapor mainly came from tropical oceans, and the South China Sea contributed the most, the local and surrounding near surface atmosphere with high specific humidity also contributed significantly. On August 9, the water vapor mainly came from the high specific humidity atmosphere in the near-surface layer of the inland, followed by the South China Sea.

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.

Based on the observation data of thunderstorm from 1998 to 2015 and the observation data from automatic weather stations at Changle Airport, daily reanalysis data from NCEP during 2010-2015, the temporal distribution characteristics of thunderstorm weather accompanying with wind shear at Changle Airport were analyzed, and the circulation types were summarized. Results show that the thunderstorm weathers occurred over Changle Airport all the year round, and it was most frequent in summer and its duration was longer. The daily change of thunderstorm weathers was obvious, it mainly occurred from the afternoon to the evening, and the duration was generally less than 2 hours, the majority of thunderstorms lasted less than an hour. The thunderstorm weathers occurred most easily in the westerly direction of Changle Airport. The probability of occurring wind shear from 3 hours before to 3 hours after the thunderstorm was 54%, and the probability of thunderstorms accompanying with wind shear in the westerly direction of Changle Airport was higher than that in other directions. The frequency of weak wind shear was much higher than that of moderate wind shear in Changle Airport, while the frequency of strong wind shear was the least. There were four main types of circulation situation for thunderstorm weathers accompanying with wind shear, they were the southern trough type, subtropical high control type, North China trough type and tropical cyclone type.