What is the temperature when frosting?

In first frost, the temperature is about 10℃-20℃. When the temperature of the local watch is below zero degrees Celsius, it will frost. Frost is a white ice crystal formed by the air near the ground being cooled by the radiation of the ground to below the frost point and condensing on the ground or objects.

Lu You wrote in Frost Moon that "the withered grass is frosty and gray, and the cold window is full of new shadows." It shows that frost appears on a clear moonlit night in autumn. There are no clouds in the autumn night, and the ground is like a quilt, which radiates a lot. When the temperature suddenly drops below 0℃, the water vapor on the ground will condense on streams, bridges, leaves and soil, forming tiny ice needles, and some will become hexagonal frost flowers. Frost can only form on sunny days. People say that "the thick frost is fierce" is the reason.