What are the phenomena of snowfall, politics and clear skies in Gansu?

Clear sky snowfall:197565438+February 10, it snowed for five consecutive days in Hezheng County, Gansu Province. After the weather cleared up at night, rare clear-sky snowfall was observed. In fact, when the formation layer of snow particles is very thin and the concentration of snow particles is very small, they scatter and refract light weakly, and snow seems to fall from the "clear sky".