Stable

stable lapse rate plotted on a skew-T diagram

On this plot, if a parcel of air with temperature T and dewpoint Td is lifted, it will move along the dry adiabat until it reaches saturation at Point T1. If the parcel is lifted further, it will then ascend along the moist 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. Thus it will always tend to return to its equilibrium state. This air is said to be stable.

Note that a parcel lifted to T2 would not subsequently sink back down to it original position. The parcel became saturated in the lifting process and was lifted moist adiabatically above the LCL. When the stable parcel at T2 descends, it follows a dry adiabat to a point where it intersects the observed temperature curve. This occurs at about the 730 hPa level.

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