There are two types of frost: radiation and advection.
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Radiation frost is the most common and is characterized by the normal cooling of the soil during the night. During the day, the sun heats the soil and it stores heat. At sunset, the thermal radiation starts to pump heat from the ground into the atmosphere, which cools the first few metres in contact with the ground. A thermal gradient is set up and can be as high as a few degrees per hour, which can cause a sharp decrease in ground temperature over the course of the night. The presence of clouds can reduce the ground's thermal losses which then cools down less than on a clear night. Other meteorological parameters, notably the wind and the thermal amplitude the day before, can also affect the temperature drop during the night. At sunrise and as the first rays of sunlight appear, it takes a varying amount of time (one to two hours) before the temperatures go back up and thermodynamic phenomena can cause a drop in temperature in the early morning.
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Advection frost, which is rarer, is characterized more by the arrival of a cold air mass and wind.
When the humidity is high, "white frost" occurs, otherwise there is "black frost". The lower the temperature, the less water the air contains at the same relative humidity. The wet temperature differs from the dry temperature of the air given by conventional thermometers in that it takes into account the humidity of the air. There are wet/dry temperature tables which allow the conversion to be made.