Atmospheric condition in which the environmental lapse rate (ELR) is greater than the saturated adiabatic lapse rate (SALR) but lower than the dry adiabatic lapse rate (DALR), and stable, saturated air (i.e. air at the same temperature and density as the surrounding air, and so possessing neutral buoyancy) is forced to rise, e.g. to cross a mountain barrier. As the air rises it cools at the SALR, but since this is less than the ELR the rising air is warmer than the surrounding air at every height and, therefore, more buoyant, and it continues to rise. It is then unstable, its instability being conditional on the air being forced to rise. The air ceases to rise when condensation has removed sufficient moisture for it to cease to be saturated, when it will cool at the DALR, which is less than the ELR, so the air once more becomes neutrally buoyant and stable.