Formation of Dew and Frost

  • Dew - forms when the temperature cools to the dew-point temperature -->>

  • If T = Td < 32°F, get frost

  • dew/frost often form only close to the ground, e.g., not on a bush, why??  ANSWER 

  • Dew and frost most often form on clear, calm nights..., why??  ANSWER

  • Dew can be an important source of moisture during periods of low rain fall.

QUESTION FOR THOUGHT:

1.  Explain the reasoning behind the wintertime expression, "clear moon, frost soon."

2.  While driving from cold air (well below freezing) into much warmer air (well above freezing), frost forms on the windshield of the car. Does the frost form on the inside or outside of the windshield? How can the frost form when the air is so warm?