Why doesn't it snow in winter in Heze, but only sleet (it snowed once in Heze, but it was artificial snowfall)?

Heze is located in the middle of Shandong Province, China, and belongs to the temperate monsoon climate zone. Because it is located inland and influenced by continental climate, the temperature in winter is low, but the precipitation is less. This climatic condition makes Heze less prone to large-scale snowfall in winter, but more prone to sleet or rain. In addition, artificial snowfall may be because the local meteorological conditions are not conducive to natural snowfall. In order to meet specific needs, artificial intervention is taken for snowfall.