-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 dualpolarization radar products that there were obvious twolayer 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."/>