What condition must exist for clouds, fog, or dew to develop?

For clouds, fog, or dew to develop, the essential condition that must be met is that water vapor condenses. This process occurs when water vapor in the air cools and changes from a gaseous state to a liquid state, forming tiny water droplets. These droplets cluster together to create clouds, fog, or dew, depending on the environmental conditions.

When the air temperature drops or when the air becomes saturated with moisture, the capacity of the air to hold water vapor decreases, leading to condensation. This is often observed during the cooling of air at night, which leads to dew formation or when moist air rises, cools, and forms clouds.

High temperatures are not conducive to cloud formation because warm air can hold more moisture, making it less likely for condensation to occur. Low humidity means there is a lower amount of water vapor in the air, further reducing the likelihood of condensation. Strong winds can disperse moisture and prevent the cooling necessary for condensation, which also does not favor the development of clouds, fog, or dew. Thus, the ability for water vapor to condense is the fundamental requirement for these atmospheric phenomena to occur.