3. Stability

Determining Stability » The Parcel Method Stable

When a lifted parcel has a lower virtual temperature than the surrounding environment, the parcel will be denser than the environment. In this case, the displaced parcel tends to return to its original position and the environment is said to be stable. Under the same conditions, a sinking parcel will have a higher virtual temperature then its surroundings, which will cause it to rise toward its original position.

It is worth noting that the normal condition for the atmosphere is that it is stable, except where certain processes, such as strong surface heating, upward motion, etc. render an unstable condition. Recognizing the impact of such processes on the stability is a critical forecast problem, and is addressed later in the Changing Stability section.