It results from a thin coating of ice crystals deposited directly on surfaces by sublimation of atmospheric water vapor. In the formation of white frost, the liquid stage between vapor and solid is normally omitted. The other type of frost, which is usually confined to very dry climates, is black frost . Then when the temperature rises, the vegetation blackens, thus the term black frost. It is difficult to measure the exact temperature of surfaces where frost deposits occur.
Air temperature is usually different from surface temperatures.
Because of this and the fact that air temperature records are available for many years back, the usual practice is to associate air temperature records taken in standard weather instrument shelters with the occurrence of observed frost and freeze damage on openly exposed surfaces. Frosts Frosts in early fall and late spring. These unseasonable occurrences are due to excessive radiant heat loss from soil and crop surfaces under clear skies and subnormal air temperatures. Radiation frosts and freezes require cool dry air, clear conditions and little or no wind during the night and early morning hours. Frosts in early spring and late fall.