A moist, unstable air mass is typically characterized by?

A moist, unstable air mass is characterized by cumulus clouds, which form as warm, moist air rises and cools, leading to the development of thermal lift. This rising air frequently leads to the formation of towering cumuliform clouds that can produce convective activity, such as showers or thunderstorms. The instability in the atmosphere allows for rapid vertical development of clouds, which is evident in the presence of cumulus and cumulonimbus clouds, commonly associated with showery precipitation.

In contrast, the other choices present characteristics associated with different atmospheric conditions. Poor visibility and smooth air usually stem from stable air that promotes stratiform cloud development rather than cumulus clouds. Stratiform clouds primarily produce continuous and steady precipitation, indicating a stable air mass rather than the instability that defines moist air masses. Lastly, calm winds and clear skies are indicative of a stable environment, where the air does not rise significantly, contradicting the nature of an unstable air mass. Thus, choice B accurately reflects the characteristics of a moist, unstable air mass.