Frost temperatures are generally below 0°C. Frost season, if there is a strong cold air southward, the ground surface temperature drops to 0 ° C or below, the water vapor in the air near the ground is saturated, it will be on the ground or near the ground objects directly condensation formation of fine ice crystals. Frost is usually formed on clear, breezy or windless nights during the cold season. The appearance of frost indicates that the local night weather is clear and cold, the atmosphere is stable, and the ground is strongly cooled by radiation. This usually occurs when there is a cold air mass in control, so it tends to maintain good weather for a few days.

The formation of frost is related to weather conditions, but also to the properties of the object to which it is attached. The temperature of the surface of the object is very low, while the air temperature near the surface of the object is relatively high, then there is a temperature difference between the air and the surface of the object. If the temperature difference between the surface of the object and the air is mainly caused by the radiative cooling of the surface of the object, the air cools down when the warmer air comes into contact with the colder surface of the object and reaches a point where it is supersaturated with water vapor when the excess water vapor is precipitated out. If the temperature is below 0°C, the excess water vapor condenses into ice crystals on the surface of the object, which is the frost.