Diagnostic analysis of a multi-phase frontal precipitation process in winter in Guizhou

On February 3, 2024, a rare complex phase precipitation process with freezing rain, snow, hail, and rainstorm in winter occurred in Guizhou. Based on the conventional meteorological observation data, FY-4A satellite cloud image, doppler weather radar data, and the fifth-generation atmospheric reanalysis data from the European Centre for Medium-Range Weather Forecasts, the precipitation evolution, the frontogenesis and instability mechanisms of this process were studied by weather analysis and diagnosis method. The results show that: (1) This weather process is a frontal precipitation weather formed by the development of southwest airflow in front of the south branch trough, the continuous strengthening of cold and warm air, and the interaction of Yunnan-Guizhou quasi-stationary frontogenesis. (2) The mesoscale precipitation belt crosses the Yunnan-Guizhou quasi-stationary front, with its western section developing rapidly and intensely. The precipitation echo has the characteristics of the cumulus cloud echo, resulting in strong convective weather of hail and short-term heavy precipitation. However, the eastern section of the precipitation belt shows weaker precipitation intensity, with characteristics of stratified mixed echo, higher echo top, and the development of ice crystal layer, resulting in the transition between rain and snow phases. (3) The southwestern Guizhou in the western part of the precipitation belt is in the warm air mass ahead of the quasi-stationary front. The rapid warming and humidification in the afternoon and the conditional static instability lead to the formation and development of vertical convection. The northeastern part of Guizhou in the eastern section of the precipitation belt is behind the quasi-stationary front, and the vertical distribution of temperature presents a three-layer structure. Affected by the enhancement of cold air, the temperature of the whole atmosphere decreases, the melting layer weakens, and the development of the cold layer and the ice crystal layer strengthens. The quasi-stationary front is generated with the conditional symmetric instability, leading to the upward movement along the frontal zone and the transition from rain to snow.