What is a key feature of unstable, moist air?

A key feature of unstable, moist air is the formation of cumuliform clouds and showery precipitation. This type of air is characterized by significant vertical movement, which can lead to the development of towering cumulus clouds and can produce thunderstorms or showers. The instability allows warm air to rise rapidly, creating the conditions necessary for convective activity.

In contrast, stratiform clouds and steady rain are associated with stable air, where less vertical mixing occurs and the air tends to be more horizontal. High humidity and low visibility are more general characteristics that can occur in various situations, but they do not specifically indicate the instability of the air. Surface winds and fog formation are also related to specific weather phenomena but do not directly highlight the characteristics of unstable, moist air. Therefore, the formation of cumuliform clouds and the occurrence of showery precipitation is the most definitive feature indicating instability in moist air.