What is a characteristic of stable air?

A characteristic of stable air is indeed the presence of stratiform clouds. In stable air conditions, vertical motion is limited, which leads to the formation of layered clouds that spread out horizontally instead of developing vertically. This results in clouds that are generally smooth and uniform in appearance, such as stratus or nimbostratus clouds, which are indicative of stable atmospheric conditions.

In contrast, fair weather cumulus clouds are typically found in unstable air where rising thermal currents allow for vertical development. Rapid decreases in temperature with altitude are associated with unstable air, which promotes convection and cloud growth. Lastly, stable air is characterized by low turbulence, as the lack of vertical motion leads to a more stable and calm atmospheric environment, making turbulence conditions less likely to occur.