一次“梅中返春”稳定性持续暴雨过程的预报失误分析

使用NCEP-FNL资料对杭州湾一次稳定性持续暴雨过程进行分析,发现冷暖气流在浙江不断交绥形成持续降雨,低层冷空气和东南暖湿气流的不断增强,使大气斜压扰动发展,锋区降雨增强,暴雨发生。此次过程,由于数值模式预报出现偏差而导致杭州湾24h大雨、暴雨预报出现较大失误。检验结果,GFS模式36h预报时效内对冷暖系统预报较好,但对低层锋区的风场预报有偏差,从而对中低层辐合、水平锋生和水汽输送产生影响,大雨、暴雨落区出现偏差。另外,模式对杭州湾南岸冷空气影响预报偏弱也是暴雨漏报的一个重要因素。稳定性降雨预报中,预报员需重视模式在预报临近时刻的调整,根据实况监测和雨带的移动、演变对冷暖气流影响作甄别,从而及时调整降雨落区和影响时间,对预报做出有益修正。

Analysis of Forecast Error in a Continuous Heavy Rain Event During the Spring Like Plum Rain Season

Using NCEP-FNL data, we analyzed a continuous heavy rain process in Hangzhou Bay, and found that the constant intersection of cold and warm flows in Zhejiang Province caused the continuous rainfall. The increase of low level cold air and southeast warm and humid air resulted in the development of baroclinic atmosphere disturbance, the enhancement of rainfall in the frontal area and the occurrence of heavy rains. Due to the deviation of the numerical model forecast, a large error occurred in the 24 h forecast of heavy rainfall in Hangzhou Bay during this process. The test results showed that the GFS model is better for the prediction of the cold and warm system in 36 h lead time, but has an error for the wind forecast in the low-level front, which affected the convergence, horizontal frontogenesis and the transportation of water vapor in the low middle layer, leading to the deviation of falling area of heavy rain and rainstorm. In addition, it is also an important factor in the rainstorm forecast error that the model is weak in forecasting cold air in the south bank of Hangzhou Bay. Therefore, for rainfall stability forecast, forecasters need to attach importance to model adjustment in the prediction at adjacent time, and judge the influence of cold and warm air flow according to actual monitoring and the movement and evolution of rain belt, so as to timely adjust the rainfall zone and influence time and make an effective correction to forecasts.