How do clouds form? What is the difference between Fog and Frost?
If the air temperature cools below the dew point, water vapor will condense and form cloud of fog drops.
Fog: If the air temp cools below the dew point ABOVE freezing, water vapor will for dog not frost.
Frost: If the temperature is below freezing, the dew point is called the frost point, and if the surface temp falls below the frost point, the water vapor is deposited directly as ice crystals. (deposition)