Final answer:
Adiabatic cooling leads to the formation of widespread Nimbostratus and Altostratus clouds by causing rising air to expand and cool, condensing water vapor into cloud droplets.
Step-by-step explanation:
The process in an air mass that leads to the creation of widespread NS (Nimbostratus) and AS (Altostratus) cloud coverage is adiabatic cooling. This occurs when an air mass rises and expands in the atmosphere, leading to a decrease in temperature without the exchange of heat with its surroundings. As the air rises, it eventually cools to the point where water vapor condenses into cloud droplets, forming extensive layers of cloud cover. In the context provided, the heat gained by the atmosphere when water vapor condenses plays a significant role. This energy release can cause the air to rise even further, contributing to the cloud formation process; however, the feedback mechanism described primarily relates to the development of thunderheads, not necessarily widespread NS and AS clouds.