What is the first frost temperature?

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.

Frost refers to white ice crystals that condense on the ground or objects when the air near the ground is cooled below the frost point (dew point is below 0) due to the radiation cooling of the ground. Frost is a weather phenomenon, which belongs to ground meteorological observation in China. "Frost" usually appears from autumn to spring. Meteorology generally refers to the early frost in autumn as "first frost" or "first frost", and the final frost in spring as "late frost" or "final frost". The interval from the last frost to the first frost is a frost-free period.

Scientifically speaking, frost is made up of ice crystals, similar to dew. When the relative humidity in the air reaches 100%, water is separated from the air. The only difference between them is that the dew point (the temperature at which water vapor liquefies into dew) is higher than the freezing point, while the frost point (the temperature at which water vapor condenses into frost) is lower than the freezing point, so frost will only appear when the near-surface temperature is lower than 0℃.