Analysis of weather characteristics and sea surface temperature impact on rainfall/snowfall and freezing events in Hubei Province in February 2024

In February 2024, Hubei Province experienced two low temperature, rainfall/snowfall and freezing events. Particularly, the damage caused by freezing rain was especially severe. To analyze the causes of the two rainfall/snowfall and freezing events, the reanalysis, the sea temperature and circulation index, the daily observation data from 82 national meteorological stations in Hubei Province since 1961 were used. Based on the improved composite index of persistent low temperature, rainfall/snowfall and freezing intensity, these two events characteristics were compared with the strongest rainfall/snowfall and freezing weather in 2008. Then the circulation anomalies and the influence of sea surface temperature (SST) of these two events was analyzed. The results are as follows. (1) During the two events in February 2024, the rain and snow phases were more complex, with a larger freezing rain range and stronger extremity compared to those in 2008. But the duration and snow depth were less severe than those in 2008. (2) The 500 hPa geopotential height anomaly was a typical “low in the west and high in the east” distribution, which is favorable for precipitation. The anomaly of the western Pacific subtropical high (WPSH) was enhanced, combined with the cold air from the east, forming persistent low temperature, rainfall/snowfall and freezing weather. The first event had deeper warm layer conditions and stronger southwest water vapor, mainly dominated by freezing rain. The second event featured stronger cold air but weakened southwest water vapor, which was dominated by a mix of ice particles, graupel, and freezing rain, with more complex precipitation phases. (3) The two events in February 2024 occurred under the background of a moderately strong El Niño event reaching its peak and beginning to weaken. The Indian Ocean was abnormally warming and exhibited a distribution pattern of "warm in the west and cold in the east", which played an important role in the abnormal enhancement of the WPSH and the abnormal enhancement of water vapor in the south in the late winter. (4) The abnormally warm SST near the Yellow Sea to the Sea of Japan forced an anomalous anticyclonic circulation over the Sea of Japan, blocking the eastward movement of the westerly wind belt. The southward movement of cold air converged with the enhanced WPSH transporting southern water vapor, resulting in sustained rainfall/snowfall and freezing weather.