Abstract: Based on dense snowfall observations,multi-source observational data and ERA5 reanalysis data,this study analyzes the precipitation phase transition,snow depth characteristics,and key forecasting issues of a severe rain-snow event that occurred over Liaodong Peninsula on February 14,2020.The results show that this severe rain-snow event occurred under the combined influence of the upper-level cut-off low,low-level southwest jet,shear line,and surface cold front.This event was characterized by strong snowfall intensity,a concentrated period of heavy snowfall,and complex rain-snow phase transition,making the forecasting of precipitation phase and hourly snow depth the main challenges during this event.Under the influence of bottom cold air,the increase of frozen layer thickness is the main reason for precipitation phase transition.During the rain-snow transition,the vertical distribution ranges of liquid-phase and ice-phase particles within the cloud exhibited a substantial overlap,while the thickness of the low-level melting layer decreased significantly.Variations in snow depth and snow-to-liquid ratio were related to the configuration of upper-level temperature,relative humidity,and vertical velocity.The decrease of super-cooled water droplet content during particle descent favored the formation of a larger snow-to-liquid ratio.During this event,snow accumulation occurred when the 2 m air temperature was below -3 ℃ and the surface temperature was below -1 ℃.Higher snow-to-liquid ratios were mostly observed during the warming stage following an initial decrease in surface temperature.