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What Causes Frost?

Frost occurs when the following three things happen:

1. The surface on which the frost forms must be at the temperature of 32 degrees F or lower
2. Conditions must be calm, with little or no wind present.
   
3. The surface temperature must efficiently cool air to its dew point.

While the first two conditions can readily occur both day and night, it is difficult to achieve the third condition during daylight hours because of the heating by the Sun. At night, when it’s dark, temperatures can fall (especially under a clear sky) to dew point. If the temperature is about 32?F, dew will form. If the temperature falls below 32F, frost will form. Dew and frost usually form after several hours of darkness.