Abstract: Based on the routine upper level and surface meteorological observation data, the temperature of black body(TBB) data from FY-2G satellite and ECWMF dataset with a spatial resolution of 0.125°×0.125°, a regional snowstorm occurring in Shaanxi Province on 3 January 2018 was analyzed. The results show that the regional snowstorm occurred under the background of 500 hPa deep trough caused by cut-off low, 700 hPa southwest jet and 850 hPa easterly air flow. The efficient water vapor from Bay of Bengal and East China Sea was transited by strong low level southwest jet and easterly air flow, respectively, which was one of the main causes of the snowstorm. The intrusion of cold flow in middle level was the main trigger mechanism. Strong upward motion caused by the upper level divergence and low level convergence and the development and maintenance of positive vorticity in middle and low level were the dynamic mechanism of the snowstorm. The meso-β scale convective cloud cluster with minimum TBB  of -50 ℃ developed in the process of eastward moving of convective cloud cluster with the length of 1100 km, the width of 40 km and TBB equal to or less than -40 ℃, which caused the short-time heavy snowfall with precipitation intensity more than or equal to 2 mm·h-1. As an elevated convection case, the updraft increased due to the slantwise convection triggered by conditional symmetric instability. The echo band was parallel to 0-6 km vertical wind shear, and the snow area was consistent with the moving direction of the flow.

Key words: regional snowstorm, cut-off low, low level jet, middle level cold air, slantwise convection

摘要： 利用高空、地面常规观测资料，FY-2G黑体亮度温度TBB资料和ECWMF 0.125°×0.125°高分辨率资料，对2018年1月3日陕西区域性暴雪进行诊断。结果表明：500 hPa切断低压分裂低槽、700 hPa西南急流和850 hPa东风回流是暴雪发生的主要影响系统。700 hPa强西南急流、偏东气流分别携带来自孟加拉湾和东海的充沛水汽是产生区域性暴雪的重要原因之一；中层冷空气的侵入是本次暴雪发生的主要触发机制；高层辐散与低层辐合的有利配置导致的强上升运动和中低层深厚正涡度的发展和维持是暴雪形成的动力机制。长约1100 km、宽约200 km、TBB≤-40 ℃的狭长云带东移过程中发展的TBB最低为-52 ℃、尺度为20～100 km的中-β尺度对流云团是造成小时降雪量超过2.0 mm、产生区域性暴雪的主要原因。本次暴雪属于冷季高架对流，对称条件不稳定导致的倾斜对流使上升运动加强，雷达回波表现为平行于0～6 km垂直风切变的平行带状结构，且雪带随气流移动。

关键词: 区域性暴雪, 切断低压, 低空急流, 中层冷空气, 倾斜对流