Although you may not have realized it, you’ve probably walked through a cloud! You see, not all
clouds form high in the atmosphere. Some clouds form at ground level. These low-lying clouds are called fog.

 

Sometimes, a phase change from a gas to a liquid produces liquid water without clouds. This often occurs at night and in the early morning hours when the ground is chilled. Air that remains in contact with chilled surfaces loses the heat energy that keeps water in its gaseous phase. As a result, some of the water vapor molecules undergo condensation and collect as tiny droplets on leaves, grass, cars, and other surfaces. This liquid is called dew.

 

When surface temperatures drop below freezing, and sufficient water vapor is present in the air, the water vapor will undergo a phase change of deposition and form ice on the surface. Instead of forming liquid dewdrops, a thin coating of frost appears.