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Using conventional meteorological observation data, lightning location data, ERA5 reanalysis data and dualpolarization radar data, an extreme “thunder snow” process in Northwest Shandong Province from 6 to 7 November 2021 is analyzed. The results show: (1) Thunderstorm and snowfall occurred 150 km behind the cold front, which belonged to the cold front type elevated convection in winter. The duration and frequency of lightning had a good corresponding relationship with the snowfall. (2) The circulation pattern was characterized by “cold at the bottom and warm at the top”. The lower layer was the “cold layer” behind the cold front, and the “warm layer” formed by the southwest warm and humid airflow near 800 hPa. The southwest lowlevel jet and the northeast wind ultralowlevel jet were exceptionally strong, which not only provided sufficient water vapour for the convective generation but also made the deep vertical wind shear reach 6.7×10^-3 s^-1, which was conducive to increasing the stratification instability. (3) Before the occurrence of “thunder snow”, the atmosphere over Northwest Shandong was convective instability. The cold surface gradually thickened with the invasion of cold air, and there was conditional symmetric instability near the cold front over Northwest Shandong. The mesoscale vortex at 800 hPa triggered convection above the inversion layer and generated lightning. (4) It could be seen from the dualpolarization radar products that there were obvious twolayer echoes around the station when thunder snow occurred, and the concentration of ice phase particles at -10 ℃ layer height (about 600 hPa) was relatively large, which might be one of the lightning mechanism.