In order to strengthen the understanding of the low visibility impact events on the navigation meteorological conditions of the Yangtze River trunk line and improve the level of weather forecast for channel impact, using observational data from the National Meteorological Station and ERA5 reanalysis data (the fifth ECMWF reanalysis), we conducted an analysis of the spatiotemporal distribution characteristics of fog days at 51 stations along the Yangtze River, as well as the weather conditions and meteorological element changes during fog occurrences. The main findings are as follows: (1) Most stations along the river experienced a high incidence of fog from November to next January. The Sichuan and Chongqing area exhibited a consistently high fog occurrence throughout the year, while in the Hubei-Anhui Plain region fog incidents are frequent in spring. Thick fog and heavy fog predominantly occurred during the late-night and early morning hours, with strong fog typically occurring about 2 hours later. (2) In winter, fog along the Yangtze River primarily occurred in the Sichuan section (Yibin-Chongqing), the southwest and central sections of Chongqing (Chongqing-Wanzhou), followed by the Anhui section (Anqing-Hexian) and the Jiangsu section (Dantu-Taicang). (3)When fog was present along the river, the average 10-minute wind speed ranged from 0 to 3 m·s^-1, occasionally exceeding 4 m·s^-1. Northerly wind is the main wind, followed by easterly wind and westerly wind.(4) Mountainous areas along the Yangtze River exhibited a high proportion of rain and fog, with a notable frequency of thick fog, which was strongly correlated with precipitation. In contrast, in plain areas, radiation fog in early morning was more prevalent, and the occurrence of thick fog was often not directly linked to precipitation. The proportion of rain and fog in the eastern plain area was similar to that in mountainous areas, with relatively minor station-to-station fluctuations. (5) Strong fog weather events were associated with four primary near-surface weather situations: the low-pressure rear type, low-pressure trough type, weak high-pressure type, and high-pressure bottom type. Among them, the weak high-pressure type had the highest incidence, followed by the low-pressure trough type, while low-pressure rear type and high-pressure bottom type were less common.

Based on the meteorological observation data of 735 stations in the Yangtze River Basin from June to July during 2016-2020, NCEP/NCAR reanalysis data and basin rain information, the regional characteristics, the weather system and causes of main rainstorm processes in the Yangtze River Basin were discussed preliminarily. The results are as follows: (1) The precipitation from June to July during 2016-2020 was mainly affected by the Meiyu front caused by the strengthened west Pacific subtropical high and the eastward movement of the upper low trough in the middle and high troposphere over the Yangtze River Basin. The main influencing systems in the middle and low layers were shear line, vortex and typhoon inverted trough. Half of the precipitation processes in the boundary layer occurred in the warm region or influenced by the static front. (2) The main weather patterns affecting rainstorm processes in the Yangtze River Basin were divided into zonal circulation type, the type between two highs (western Pacific subtropical high and south Asian high), meridional type and easterly flow type. (3) The precipitation difference in the Yangtze River Basin had a good correlation with the subtropical high ridge line location, the northward push process of summer monsoon and the short-term strong precipitation area.