What indicates a stable air mass?

A stable air mass is characterized by a situation where air parcels that are lifted tend to return to their original position rather than continuing to rise. Stratiform clouds and fog are indicators of stable conditions because they form when air is saturated and there is minimal vertical movement in the atmosphere. This typically results from cool, moist air being found under a warm, stable air layer, which suppresses turbulence and the vertical development of clouds.

In contrast, other indicators such as rapid fluctuations in temperature with altitude suggest instability in the atmosphere, as do high levels of turbulence. The development of thunderstorms is also associated with unstable air masses, where warm, moist air can rise rapidly, leading to convection and storm development. Thus, stratiform clouds and fog effectively signal stability in the air mass, as they occur under conditions where vertical air movement is minimal.