If the temperature remains unchanged or decreases slightly as altitude increases, what does this indicate about the air mass?

When temperature remains unchanged or decreases slightly with increasing altitude, it suggests that the air mass is stable. In stable air, vertical movements are inhibited, which means that air parcels tend to resist rising or falling once they are disturbed. This occurs because colder air is denser than warmer air, causing any upward-moving air to cool down and subsequently descend, thus maintaining stability.

A temperature inversion typically occurs when the temperature increases with altitude rather than decreases. This creates a cap that limits vertical mixing and is often associated with stable conditions, but in this scenario, the primary characteristic of the air mass is its stable nature due to little to no change in temperature with altitude.

Unstable air, on the other hand, usually occurs when the temperature decreases rapidly with altitude, creating conditions where warmer, less dense air can rise more easily. Moist air relates to humidity levels within the air mass but does not directly indicate stability concerning temperature changes with altitude. Therefore, the best assessment of the air mass in the situation described is that it is stable.