Determining Stability » Stability Types Absolutely Unstable

On this plot, the red line (line T-T’) depicts an observed temperature profile from the surface (near 960 hPa) to 850 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. At every point in its ascent, the parcel is warmer than the surrounding air (line T-T’). As a result, the air along path T-T1 will be warmer and less dense than the surrounding air. Consequently, it will continue to rise of its own accord. This air is said to be "absolutely" unstable. The sounding lapse rate from T-T’ exceeds dry adiabatic and is therefore commonly referred to as a superadiabatic lapse rate.
Note that absolute instability is a relatively rare condition and usually confined to a shallow layer near the surface under conditions of strong surface heating (for example, solar heating or very cold air over warm water).