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A short-time heavy precipitation process triggered by a cold front in the Hanjiang Basin of southern Shaanxi and its precipitation forecast verification
XIAO Yiqing , MA Yongyong , CHEN Xiaoting , AN Dawei , HUANG Shaoni
Journal of Arid Meteorology    2023, 41 (6): 972-983.   DOI: 10.11755/j.issn.1006-7639(2023)-06-0972
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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.

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