Based on multi-source observation data such as millimeter-wave cloud radar, precipitation phenomenon instrument, wind profiler radar, dual-polarization radar, automatic weather station, and ECMWF (European Centre for Medium-Range Weather Forecasts) Reanalysis v5 (ERA5), the circulation background and microphysical parameters of precipitation particles during the snowstorm in Shandong on 14 December 2023 are analyzed. The application of new observation data in precipitation phase monitoring and forecasting is discussed. The following results are obtained. (1) The extreme snowfall is affected by the upper-level trough, the southwest low-level jet, and the Jianghuai cyclone. With the decrease of the surface temperature and the retreat of the middle-level warm layer, there occurs rain, sleet, ice particles, and snow from west to east in Shandong. (2) The precipitation phenomenon instrument suggests that the terminal velocities of snow and rain are low. The diameter of snow particles exceeds 8 mm, and the diameter of rain particles is mostly below 4 mm. (3) The millimeter-wave cloud radar observes that the sleet turns to snow when the reflectivity, radial velocity, spectral width, and vertical liquid water content are reduced. (4) The wind profile radar finds that the phase of sleet and ice corresponds to the strong southwest low-level jet and the maximum vertical velocity (4-5 m·s^-1). When it turns to snow, the vertical velocity below 3 km decreases to about 2 m·s^-1. (5) The dual-polarization parameters such as correlation coefficient C_c, differential reflectivity Z_DR, and reflectivity Z_h can judge the bright band of melting layer, and the decline and disappearance of the bright band can indicate the conversion of rain to snow.