贵州西部一次秋季暴雨预报偏差分析

2021年9月16日预报夜间贵州西部将出现暴雨-大暴雨天气,实况以小到中雨、分散暴雨为主,本文利用常规及加密观测资料、NCEP/NCAR再分析资料、ECMWF、CMA-GD、CMA-SH9等模式预报产品,对这次暴雨空报的原因进行探讨,结果如下：(1)本次暴雨-大暴雨空报的主要原因：副高夜间略北推增强,有利下沉气流增强,阻止切变线南下且消弱低层切变的强度;整体动力条件较差,低层辐合厚度、强度不够,且迅速转为辐散,涡度平流由正转负、上升运动较弱。(2)模式出现较明显误差：ECMWF错误预报副高夜间位置,切变线位置预报也有偏差,CMA-GD模式错误预报切变线位置;5家数值模式预报量级均偏大,其中CMA-GD、CMA-SH9及贵州WRF偏大明显,ECMWF的量级及落区预报和实况更为接近。(3)预报员过度相信ECMWF对切变线的位置预报、过度相信CMA-GD对极端降水的把握,忽视副高略北推增强、动力条件差导致的触发难度迅速加大,主观预报的优势没有发挥出来。

Deviation analysis of a rainstorm forecast in autumn in Guizhou

On September 16, 2021, it is predicted that there will be rainstorm heavy rainstorm weather in western Guizhou at night. The actual situation is mainly small to moderate rain and scattered rainstorm. This paper uses conventional and encrypted observation data, ncep/ncar reanalysis data, ECMWF, CMA-GD, CMA-SH9 and other model prediction products to discuss the causes of this rainstorm air report. The results are as follows: (1) the main causes of this rainstorm heavy rainstorm air report: the subtropical high is slightly pushed northward at night, and the favorable downdraft is enhanced, Prevent the shear line from going down to the South and weaken the strength of low-level shear; The overall dynamic conditions are poor, the convergence thickness and intensity in the lower layer are not enough, and it quickly turns to divergence, the vorticity advection turns from positive to negative, and the upward movement is weak. (2) There are obvious errors in the model: ECMWF incorrectly predicts the night position of the subtropical high, and there are also deviations in the prediction of the shear line position, and CMA-GD incorrectly predicts the shear line position; The forecasting magnitude of the five numerical models is relatively large, of which CMA-GD, CMA-SH9 and Guizhou WRF are significantly larger, and the forecasting magnitude and falling area of ECMWF are closer to the actual situation. (3) Forecasters believe too much in ECMWF"s prediction of the location of the shear line and cma-gd"s grasp of extreme precipitation, ignoring the rapid increase in trigger difficulty caused by the slightly northward extension of the sub elevation and poor dynamic conditions, and the advantages of subjective prediction have not been brought into play.