Explain the conditions that cause or result in unstable atmospheric conditions. Hint: The following statements are descriptions of an unstable air mass, not the causes of instability: (1) In unstable conditions, when air is forced upward by an external lifting force it will continue to rise after the lifting force is removed. (2) Unstable air favors vertical movement, cumulus cloud development, turbulent conditions, and good visibility. To answer this question you need to explain the atmospheric conditions or measured characteristics that cause atmospheric instability. There is one, specific atmospheric condition that is necessary for an airmass to be unstable