Fog is a fact of life along the coast. It is especially common in the spring and fall or any time that there is a significant difference between water and air temperature. Fog is a cloud that touches the ground or the surface of a body of water. As air cools, water vapor suspended in the atmosphere condenses into water droplets, usually around minute particles of ash, dust, or even sea salt.

Find out how fog is formed.

  1. Place the jar on black paper or tape the paper on the back of the jar so you can't see through it.
  2. Fill one third of the jar with colored warm water. Have the bag of ice and matches nearby.
  3. Light the match and hold it over the jar opening.
  4. After a few seconds, drop the match in the jar and cover the top of the jar with the bag of ice.
  5. Observe the inside of the jar against the black paper background. What process(es) led to cloud formation? Why was smoke from the match important to cloud formation? (It provided particles for vapor to "grab on.")
  6. Ask students whether cold water would work as well? (no) Why? (Cool air does not rise.)

Valleys of fog

Fog can fill a valley and still leave the mountain tops with a clear view of the area. From a satellite image the fog appears in a "dendritic" pattern that follows the pattern of the valleys. What problems may be encountered in identifying fog on a satellite image?


  • a jar
  • warm water
  • a plastic bag of ice that fits over the jar opening
  • a sheet of black paper
  • matches
  • blue food coloring