What condition is least likely to occur in a stable atmosphere?

In a stable atmosphere, the vertical movement of air is limited, which reduces the potential for significant weather events such as thunderstorms. Stability in the atmosphere typically occurs when warmer air is trapped above cooler air, creating a layer in which there is little to no rising air. This lack of vertical motion inhibits the development of the strong updrafts necessary for thunderstorms to form.

High humidity, temperature inversions, and calm winds can all occur in a stable atmosphere. High humidity may be present, contributing to stable conditions but not directly contradicting them. Temperature inversions, where warmer air overlays cooler air, are a hallmark of stable atmospheric conditions. Calm winds often accompany stability, as the minimal air motion contributes to the settled nature of the atmosphere. Thus, the formation of thunderstorms is least likely in such an environment, making it the correct choice.