广东"18.8"季风槽极端降水事件对流尺度集合预报分析OA北大核心CSTPCD

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.