Late spring frosts are more problematic, causing new growth to wither and die. We ll start with a discussion of frost. Frost is the frozen version of dew, a condensation that forms when the temperature drops beyond a point where the air becomes saturated with water vapor. The excess vapor then condenses onto surfaces colder than the air. Water vapor is no more than water molecules bouncing around in the air.
Humidity is a measure of how much water vapor is held in the air.
When the temperature is high, the molecules are buzzing around, with no interest in clustering together to form droplets. As the temperature drops, the molecules slow down. At this point, they might cling together after a collision, but it isn t likely unless they have something to pattern after. This clustering around a substance for a pattern is called nucleation. As the temperature drops, the molecules can actually get colder than 32 F without freezing, if there is nothing to pattern around.