The synoptic causes and radar features were analyzed by using conventional meteorological observa-tions and Doppler radar data.The results showed that the stratification was unstable in south China.Mid-level dry air and strong vertical wind shear were the main causes of pre-TC squall line,were also the reasons that more thun-derstorm gale happened in southeast Guangxi.“Rammasun”pre-TC squall line included three short bow echoes. The eastern bow echo showed the typical features of thunderstorm gale in Doppler radar.Taking spatial applicability and time advance as the measurement,descending of reflectivity core was the most practical and optimal feature for thunderstorm gale warning,followed by mid-altitude radial convergence and surface divergence.%用常规气象观测资料和多普勒天气雷达观测资料对“威马逊”台前飑线的天气背景和雷达回波特征做了分析。结果表明：华南区域大气层结不稳定，广西东南部有中层干区和较强垂直风切变是该区域台前飑线发生和雷暴大风多发的主要天气背景成因。“威马逊”台前飑线由三段短弓形回波组成，东部弓形回波具有较典型的雷暴大风回波特征。以空间适用性和时间提前量作为衡量标准进行对比，发现反射率核心下降的实用性和预警效果最好，其次为中层径向辐合和地面辐散。
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