Abstract:Based on automatic weather station, dual-polarization radar, millimeter-wave cloud radar, temperature profiler and ERA5 hourly reanalysis data, the characteristics of the multi-source observation data of the precipitation phase change during the extreme heavy snowstorm in the western area of Shandong on 7 November 2021 are analyzed. The results show: This process is combined influenced by the westerly trough, low vortex shear line and cold front. The system has strong baroclinicity, with low-level jet. Though the snowfall duration is not long, the hourly intensity of snow precipitation is high. Therefore, Extreme heavy snowfall appears in the western area of Shandong. The multi-source observational data captures the precipitation phase and change information well in this process. Wind and vertical velocity of wind profiler radar, correlation coefficient and zero-degree bright band of dual-polarization radar, reflectivity, vertical liquid water content, velocity and spectral width of millimeter-wave cloud radar, boundary layer temperature of temperature profiler and the two-dimensional images and information of particles from the 2D video raindrop spectrometer can be used as indicators for judging the phase of the precipitation, so these provide a reference for 0—1 hour short-term nowcasting. During this process, air temperature above the ground cooled very rapidly, the rain quickly turned to snow and the sleet only lasted for a short time. The cooling of air temperature above the ground is caused by the combination of strong negative temperature advection, vertical motion and non-adiabatic effect. In the three, the effect of negative temperature advection is the largest, the precipitation diabatic effect is the second, and the vertical motion effect is the smallest. The strong negative temperature advection and the negative temperature advection intensity increasing with the decrease of height, results in the rapid cooling of air temperature above the ground.