Characteristics and causes of low-temperature rainfall/snowfall and freezing weather event in eastern Guizhou and the middle and low reaches of the Yangtze River in early February 2024

In early February 2024, severe low-temperature rainfall/snowfall and freezing weather events occurred in the eastern parts of Guizhou and the middle and lower reaches of the Yangtze River. Coinciding with the travel period of the Spring Festival, the event caused serious impacts on travel, energy supply guarantees, and people's daily lives. To reveal the exceptional characteristics of the weather event, observation data from the National Meteorological Information Center, NCEP/NCAR reanalysis data, and Huaihua dual-polarization radar data were used to analyze the characteristics and causes of rainfall/snowfall and freezing weather events. The results are as follows: (1) Severe freezing disasters lasting 4-6 days occurred in eastern Guizhou, northern and central parts of Hunan, eastern and southern parts of Hubei, and northern and western parts of Anhui. These disasters were primarily caused by two rounds of low-temperature rain and snow weather. The first round occurred around February 1 to 4, with the most severe period appearing on the 3rd. It was characterized by heavy snowfall and freezing rain, leading to rapid accumulation of snow and ice. The second round occurred from February 5 to 6, with freezing rain predominating in eastern Guizhou and northern and central parts of Hunan, and sleet predominating along the Yangtze River in Hubei and other areas, which sustained or further increased the ice accumulation. (2) The geopotential height anomaly of the mid to high latitudes in Asia showed a distribution of low in the west and high in the east, and the southern trough was active. Both provided important weather conditions for the low-temperature rain and snow weather. The strong southwest jet stream climbs along the front to form a tilted upward airflow, enhancing the precipitation intensity behind the front, and leading to the first round of the weather event. The weakening of the southern trough and the maintenance of the southern front area, the mid-to-low low-level jet, and the surface stationary front resulted in the second round of the weather event. (3) Affected by the formation and maintenance of the South China stationary front and the Yunnan-Guizhou stationary front, the range of inversion was wide, with a significant warm layer in the southern region of the Yangtze River, resulting in different phases of precipitation on the south and north sides of the Yangtze River. Meanwhile, there were significant differences in the vertical direction of the temperature and humidity fields on the north and south sides of the Yangtze River. When heavy snowfall dominated north of the Yangtze River, the temperature and humidity fields exhibited deep cold-wet characteristics, with a typical ice-phrase structure. However, when heavy freezing rain dominated south of the Yangtze River, the temperature and humidity fields exhibited a"strong warm-wet and cold-wet"feature. (4) The rapidly increasing amount of rainwater, ice, and snow formed strong wet snow and severe freezing rain on February 3-4. The low-level supercooled water of both light and heavy rain droplets coexisted in the southern region of the Yangtze River on the night of the 3rd day, while it was dominated by light rain on the night of the 5th day.