Which phenomena could indicate the end of a stable air mass?

The development of cumulus clouds is a strong indicator that a stable air mass may be coming to an end. In stable air conditions, the atmosphere is typically characterized by a lack of vertical movement, which prevents significant cloud formation beyond stratiform clouds. When cumulus clouds begin to develop, it signifies that the air is becoming less stable and more conducive to vertical lifting. This lifting can lead to the formation of larger, more convective clouds as the air parcels rise and cool, allowing for the potential development of instability in the atmosphere.

Heavy rain showers and the formation of stratiform clouds are often associated with stable air conditions rather than indicating a transition away from them. Clear sunny skies suggest stability since they typically occur in high-pressure systems where vertical motions are limited. Thus, the appearance of cumulus clouds is a clear signal that the air mass is changing, paving the way for possible weather developments such as thunderstorms or other forms of precipitation.