Which condition is NOT necessary for thunderstorm development?

A stable atmosphere is not a condition necessary for the development of thunderstorms. Instead, thunderstorms typically require instability within the atmosphere to develop. Instability allows for warm air near the surface to rise rapidly, leading to the development of cumulus clouds and eventually thunderstorms, provided there is adequate moisture and a source of lifting, such as a front or terrain.

In a stable atmosphere, the air is categorized as being resistant to vertical motion, meaning that even if moisture is present, the warm air does not rise effectively, thus inhibiting the powerful updrafts that thunderstorms require. Therefore, a stable atmosphere would actually hinder thunderstorm formation rather than facilitate it.