Excess water vapor will condense out of the air. The temperature to which air must be cooled to reach saturation is the dew point . When air expands, it cools. When air is compressed, it warms. As air moves upward in the atmosphere, the air pressure decreases.
Air expands, and cools adiabatically.
It cools and when it reaches its dew point, condensation occurs. That is, clouds form. Clouds Clouds are important because they are a visual indication of the conditions in the atmosphere. The three basic cloud forms are cirrus, stratus, and cumulus. Fog is a cloud on the ground.