2024年桂东北一次大暴雨过程空报原因分析

Analysis of the Reasons for the False Alarm of a Heavy Rainfall Event in Northeastern Guangxi in 2024

摘要:

利用常规气象观测、ERA5再分析、风廓线雷达等资料和ECMWF、CMA-MESO、CMA-GD、CMA-SH9数值模式预报产品，对2024年5月26日夜间桂东北地区大暴雨空报原因进行天气学诊断分析。结果表明：(1)26日夜间桂东北具备强降水天气发生的环流背景和能量条件，但高空短波槽的快速移出导致高空动力抬升条件不足，没有形成深厚的上升运动。(2)850 hPa西南急流中存在风速辐散使低空水汽辐合供应不足，导致分散对流单体无法发展为大范围强对流系统。(3)各家模式的预报效果较差，中尺度模式CMA-MESO、CMA-GD、CMA-SH9对26日夜间桂东北地区的回波强度和降雨量级预报均与实况相差较大，预报员取信ECMWF模式的环流形势预报，导致对高空短波槽强度预报偏强，对低空切变线和边界层锋面南下速度预报偏快。

Abstract:

Conventional meteorological data, ERA5 reanalysis data, wind profile radar data, and forecast products from four numerical models (European Centre for Medium-Range Weather Forecasts, China Meteorological Administration Mesoscale Model, China Meteorological Administration Global Data, and China Meteorological Administration - Southern Region - 9 km resolution) were used to analyze the causes of the false alarm of heavy rainfall in the northeastern Guangxi region on the night of May 26, 2024. Results show that (1) on the night of May 26, the northeastern Guangxi region had the synoptic background and energy conditions for heavy precipitation, but the rapid eastward movement of the upper - level short - wave trough led to insufficient dynamic uplift, with no deep ascending motion formed; (2) the wind speed divergence in the southwestern jet stream at 850 hPa led to insufficient low - level water vapor convergence, preventing the development of discrete convective cells into a large - scale strong convective system; (3) The forecasting performance of various models in this process was poor. The three mesoscale models—CMA-MESO, CMA-GD, and CMA-SH9—all showed significant discrepancies from the actual conditions in their forecasts of echo intensity and rainfall intensity in the northeastern Guangxi region on the night of the 26th. Forecasters relied on the circulation pattern forecasts from the ECMWF model, leading to an overestimation of the depth of the upper-level shortwave trough and an overestimation of the southward movement speed of the low-level shear line and boundary layer front.