Which statement is true about fog or cloud formation?

Which statement is true about fog or cloud formation?

• A. The suffix 'nimbus' indicates a cloud with extensive vertical development.
• B. Cumulonimbus clouds form only in stable air.
• C. Radiation fog forms on warm, windy nights.
• D. Upslope fog forms as moist air flows up terrain due to wind.

Answer: (D)

Fog is a cloud that forms at ground level when the air near the surface cools to its dew point, causing water vapor to condense into droplets. Upslope fog happens specifically when moist air is forced to rise up terrain by wind. As the air climbs, it expands and cools, roughly at the dry adiabatic lapse rate, until its temperature reaches the dew point and condensation occurs along the slope. This creates a fog layer along the hillside or mountain leeward of the moist air source, especially on humid days with steady winds. Why the other ideas aren’t correct: the term nimbus signals rain-producing clouds rather than indicating how tall a cloud gets, so it doesn’t correctly describe vertical development. Cumulonimbus clouds form in unstable air with strong updrafts, not only in stable conditions. Radiation fog forms on clear, cool nights with radiational cooling of the ground, typically with light or calm winds—not on warm, windy nights.

Fog is a cloud that forms at ground level when the air near the surface cools to its dew point, causing water vapor to condense into droplets. Upslope fog happens specifically when moist air is forced to rise up terrain by wind. As the air climbs, it expands and cools, roughly at the dry adiabatic lapse rate, until its temperature reaches the dew point and condensation occurs along the slope. This creates a fog layer along the hillside or mountain leeward of the moist air source, especially on humid days with steady winds.

Why the other ideas aren’t correct: the term nimbus signals rain-producing clouds rather than indicating how tall a cloud gets, so it doesn’t correctly describe vertical development. Cumulonimbus clouds form in unstable air with strong updrafts, not only in stable conditions. Radiation fog forms on clear, cool nights with radiational cooling of the ground, typically with light or calm winds—not on warm, windy nights.