Determining Stability » Stability Types Stable

On this plot, the red line (line T-T’) depicts a simple, stable observed temperature profile from the surface (near 960 hPa) to 400 hPa. If a parcel of air at the surface, with temperature T and dewpoint Td, is lifted, it will cool following the dry adiabat until it reaches saturation at Point T1. If the parcel is lifted further, it will then cool following the saturation adiabat to Point T2. At every point in its ascent, the parcel is colder than the surrounding air (line T-T’). Thus, the air along the path T-T1-T2 will always be cooler and denser than the surrounding air—meaning the parcel will always tend to return to its equilibrium state. This air is said to be stable.
Note a parcel lifted to T2 would not subsequently sink back down to its original position. The parcel became saturated in the lifting process and cooled moist adiabatically (along the saturation adiabat) above the LCL. When the stable parcel at T2 descends, it warms dry adiabatically to a point where its temperature intersects the observed temperature curve and the parcel will stop descending. This occurs at about the 730 hPa level.