冷空气背景下湘北地区两次预报失误的 暴雨个例分析

利用常规观测资料、FNL再分析资料、探空资料等,对2020年6月7~9日（以下简称“6?8”过程）和7月26~29日（以下简称“7?26”过程）两次冷空气背景下的暴雨预报失误案例进行对比分析。结果表明：1、两次过程环流背景相似,均有冷空气、低涡、切变线配合,且两次过程均未形成强西南急流,但由于冷空气强度、影响时间、厚度不同,造成了暴雨的空报和漏报：“6?8”过程偏东风带动弱冷空气缓慢渗透南下,在迎风坡地形作用和暖倒槽向北强烈发展的背景下有利于局地暴雨的发生和维持;“7?26”冷空气影响时间过早,强度过强,导致地面辐合线位置偏南,实况雨带偏南;且冷空气阻碍了水汽向北输送,是导致湘北地区暴雨出现空报原因之一。2、“6?8”过程大气环境场呈现不稳定状态,具备一定的水汽条件和抬升条件,预测灾害出现的位置和发生时间的潜势条件难以从现有观测资料中体现,使得预报难度加大。3、“7?26”冷空气势力过强还表现在中层冷平流较强,存在一支下沉气流,不利于强对流天气的发生发展。在季节环境背景场下,预报员需根据临近冷空气的强度、路径和影响时间进行预报订正。

Under the background of cold air in northern Hunan twice forecast errors Case analysis of rainstorm

Based on the conventional observation data, FNL reanalysis data and radiosonde data, this paper makes a comparative analysis of the rainstorm forecast errors under the cold air background from June 7 to 9 and From July 26 to 29 in 2020. The results show that: 1. The circulation background of the two processes is similar, with cold air, vortex and shear line coordination, and the strong southwest jet did not form in the two processes. However, due to the difference of cold air intensity, influence time and thickness, the empty or missing report of rainstorm was caused: During the process of "6?8", weak cold air was driven by easterly wind to penetrate southward slowly, which was conducive to the occurrence and maintenance of local heavy rain under the background of the topographic action of windward slope and the strong development of warm trough northward. The cold air of "7?26" affected too early and too strong, resulting in the location of the surface convergence line to the south and the real rain belt to the south. In addition, the cold air obstructs water vapor transportation to the north, which is one of the reasons for the empty forecast of heavy rain in northern Hunan. 2. The atmospheric environment field in the "6?8" process is unstable, and there are certain water vapor conditions and lifting conditions, which are sufficient conditions for the occurrence of disastrous weather. The potential conditions for predicting the location and time of disasters are difficult to be reflected from the existing observation data, making the prediction more difficult. 3. The strong cold air force of "7?26" is also manifested in the strong cold advection in the middle layer and the existence of a downdraft, which is not conducive to the occurrence and development of strong convective weather. Under the seasonal environmental background, forecasters need to make forecast corrections according to the intensity, path and influence time of the adjacent cold air.