Many thunderstorms undergo a three-stage life cycle:
Warm, moist air rises in a buoyant plume or in a series of convective updrafts. As this occurs the air begins to condense into a cumulus cloud. The interactions between the rising and cooling air result in the development of a positive feedback mechanism. As the warm air within the cloud continues to rise, it eventually cools and condenses. The condensation releases heat into the cloud, warming the air. This, in turn, causes it to rise adiabatically. The cloud edges during this stage are sharp and distinct, indicating that the cloud is composed primarily of water droplets. The process continues and works to form a towering cumulus cloud. The convective cloud continues to grow upward, eventually growing above the freezing level where supercooled water droplets and ice crystals coexist. Precipitation begins to form via the Bergeron process once the air rises above the freezing level. Falling precipitation and cool air entrainment from the environment start the initiation of cool downdrafts, which leads to the second stage.
Cumulus stage diagram and actual picture
Characterized by the presence of both updrafts and downdrafts within the cloud. The downdrafts are initiated by the downward drag of falling precipitation. The downdraft is strengthened by evaporative cooling, as the rain falling with the downdraft enters drier air below the cloud base and evaporates. This cold descending air in the downdraft will often reach the ground before the precipitation. As the mature-stage thunderstorm develops, the cumulus cloud continues to increase in size, height and width. Cloud to ground lightning usually begins when the precipitation first falls from the cloud base. During this phase of the life cycle, the top of the resulting cumulonimbus cloud will start to flatten out, forming an anvil shape often at the top of the troposphere.
Mature stage diagram and actual picture with anvil
Characterized by downdrafts throughout the entire cloud. Decay often begins when the supercooled cloud droplets freeze and the cloud becomes glaciated, which means that it contains ice crystals. Glaciation typically first appears in the anvil, which becomes more pronounced in this stage. The glaciated cloud appears filmy, or diffuse, with indistinct cloud edges. The cloud begins to collapse because no additional latent heat is released after the cloud droplets freeze, and because the shadow of the cloud and rain cooled downdrafts reduce the temperature below the cloud. The decay of a thunderstorm can also be initiated when the precipitation within the storm becomes too heavy for the updrafts to support, when the source of moisture is cut off, or when lifting ceases.
Diagram of decaying thunderstorm and actual photo of remnants of the anvil
The three stages of the life cycle of air mass thunderstorms: (a) cumulus stage,
(b) mature stage, and (c) decaying stage. Arrows indicate wind directions.
(Adapted from Byers and Braham, 1949)