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Frost vs. freeze
Although the terms frost and freeze are often interchanged, they describe two distinct phenomena.
- Radiation frost occurs when a clear sky and calm winds (less than 5 mph) allow an inversion to develop, and temperatures near the surface drop below freezing.
- An advective freeze is windborn and occurs when a cold air mass moves into an area bringing freezing temperatures.
| Feature | Frost | Freeze |
|---|---|---|
| Wind | <5 mph | >5 mph |
| Sky | clear | clouds may exist |
| Cold air mass depth | 30–200 ft | 500–5000 ft |
| Inversion | yes | no |
| Cold air drainage | yes | no |
| Protection | likely successful | limited success |
Types of radiation frost
Hoar frost
White frost occurs when atmospheric moisture freezes onto solid surfaces as small crystals without first condensing as dew.
Black frost
Black frost, where few or no ice crystals form, occurs when the air temperature is below freezing but above the dew point (the temperature to which air must be cooled to cause atmospheric moisture to condense). The drier the air, the lower the dew point.
