Wind Profile Characteristics That Warn of Summertime Flash Heavy Rain Events Over the Middle Reaches of the Yangtze River Basin

Abstract

Forecasting and early warnings for summertime flash heavy rain events (FHREs) in the middle Yangtze River basin (MYRB) pose significant challenges. This study examined variations in lower tropospheric wind profiles hours before these FHREs using reanalysis data and wind profile radar observations. The findings highlight wind accelerations, directional shifts, and associated vertical shears preceding FHREs, providing valuable insight for severe weather warnings. During the summers of 2010–2019, FHREs occurred most frequently and contributed significantly to total precipitation during the Meiyu period, compared to before and after. Meiyu FHREs also exhibit longer durations and nocturnal peaks. Spatially, FHRE frequency increases from northwest to southeast, with higher frequencies in the topographic areas. The discernible moisture influx 4 hr before FHREs primarily comes from southwesterly and easterly winds below 700 hPa. Before FHRE, weaker easterly winds dominated western MYRB, while strong southerly winds prevailed in the east, influenced by mesoscale cyclonic shear and low-level jets. Detailed wind changes below 4 km altitude show that over the southeastern MYRB, accelerated west-southwest winds are observed 3–4 hr before FHREs, while southerly components near the boundary layer top intensified 2 hr earlier. Within 1 hr before FHREs, the wind speeds sharply increase to peak. East of the western mountains, southwesterly winds strengthen 5 hr prior, then weaken as they shift to northerlies just before FHREs, accompanied by reinforced northerlies near the surface. Over the western mountainous area, southeasterly components below 2 km altitude increase 4 hr before FHREs, although at lower speeds.