Conditions that produce clouds involve...

• A. Clouds form when air rises due to heating but remains isolated.
• B. Clouds form when air pressure is low, air flows together and then upward where it converges and cools to form clouds.
• C. Clouds form only at very low altitudes.
• D. Clouds form when the air mass is extremely dry.

Answer: (B)

Clouds form when moist air is lifted and cools enough for water vapor to condense. When air converges at the surface, it has nowhere to spread horizontally and must rise. As the rising parcel expands in the lower-pressure surroundings, it cools (adiabatic cooling). If the air contains enough water vapor, cooling to the dew point causes condensation on tiny particles, forming cloud droplets. Without lifting or sufficient moisture, clouds don’t develop, and arguing that clouds only appear at very low altitudes or in extremely dry air doesn’t fit the needed combination of humidity and vertical motion.