Which condition indicates a potentially unstable air mass?

Variability in wind direction at multiple altitudes is indeed a key indicator of a potentially unstable air mass. When wind direction changes at different altitudes, it often leads to a condition called vertical wind shear. This shear can disrupt the flow of air and promote lifting, which is essential for convective activity. In unstable air masses, parcels of air can rise quickly, leading to the development of clouds and thunderstorms. This variability suggests that there is enough dynamic change in the atmosphere that could facilitate significant vertical movement, which characterizes instability.

The presence of stratus clouds generally indicates stable conditions, as these clouds form in stable, stratified layers of air. Similarly, stable temperature gradients suggest a lack of strong vertical motion, as layers are not conducive to mixing. Lastly, a lack of convective activity is typically associated with stable air masses where there isn't sufficient lift to cause clouds or storms. Hence, the identification of variability in wind direction as a sign of potential instability is a crucial element in understanding atmospheric dynamics.