广东“18.8”季风槽极端降水事件对流尺度集合预报分析

受季风槽影响，2018年8月30—31日华南地区出现一次极端暴雨过程，单日站点累计降水量达1?056.7 mm，刷新了广东有历史纪录以来新的极值。对于此次极端降水事件，常用的业务模式包括欧洲中期天气预报中心全球模式（ECMWF）、日本气象厅谱模式（JMA）和中国气象局广东快速更新同化数值预报系统（CMA-GD），都低估了降水强度。利用深圳市气象局业务对流尺度集合预报系统分析了此次特大暴雨过程，结果表明：对流尺度集合预报系统对本次特大暴雨过程具有比较好的预报能力，概率匹配平均最大雨量达348.7 mm·(24 h)-1，集合平均的强降水中心和观测基本一致，观测极值附近区域发生大暴雨（≥150 mm）概率最大值达到80%。选取了较“好”和较“差”集合成员预报进行对比分析，发现较“好”成员预报的强降水中心位置和观测基本一致，而较“差”成员预报的降水中心位置则偏向福建地区。较 “好”成员预报出莲花山南侧地面中尺度辐合线较长时间的维持和缓慢移动，导致强降水雨团在莲花山脉附近不断地触发和维持，同时地形的阻挡作用使得对流系统在地形附近区域持续维持，造成了罕见的特大暴雨；而较“差”成员辐合区位于莲花山以北，对流形成后向东、向北移动，最终导致强降水预报位置偏向福建地区。

Analysis of Storm-scale Ensemble Forecasts for an Extreme Rainfall Event Associated with a Monsoon Trough on 30 August 2018 in Guangdong

On 30 August 2018, an extreme rainfall event occurred in Guangdong Province with a record-breaking 24 h precipitation of 1056.7 mm. Operational forecasts from the ECMWF, JMA and CMA-GD greatly underestimated the precipitation amount. In this study, a storm-scale ensemble forecast system (SSEF) at 4 km grid spacing produced by the Shenzhen Meteorological Bureau was used to study this extreme event. The SSEF produced a high probability of occurrence for this rainfall event. The maximum ensemble probability of precipitation exceeding 150 mm day-1 was over 80%. The predicted maximum probability-matched mean rain rate was 348.7 mm day-1, and the predicted ensemble mean heavy rainfall center matched the observation well. To understand the main causes of forecast biases, the present study also analyzed the members of relatively good and bad performance in predicting the location of heavy rainfall. Close examination showed that the surface mesoscale convergence line predicted by the good member was located on the south side of the Lianhua Mountains. It moved slowly and persisted for a long time due to terrain blocking, causing heavy rainfall near the mountains. In contrast, the surface convergence line of the bad member was located north of the Lianhua Mountains. Without terrain blocking, the precipitation system moved towards the northeast, resulting in the mislocation of the forecasted heavy rainfall center.