Thunderstorms can form anywhere in the world, but usually occur most often in areas where warm air and cool air meet such as subtropical regions around the world. They develop from the fast, upward movement of warm, moist air and can occur inside warm, moist air masses and at fronts. Thunderstorms have three distinct developmental stages.
– Developing Stage
The first stage of a thunderstorm is the developing stage, also known as the cumulus stage. During this time in a storm’s life warm, moist air is lifted upwards. The moist air can rise for many reasons – the heated ground produces thermals, two winds converge and are forced upwards, or winds blow over ground that rises quickly such as a mountain range. As the moist air rises it rapidly cools into water droplets, which look like cumulus clouds to us. The condensing water droplets release heat which warms the air. The warm rises in an updraft through the process of convection.
– Mature Stage
The second stage of thunderstorm development is the mature stage. During this stage, the warm moist air continues to rise until it reaches existing air which is warmer, and it can rise no further. The air spreads out instead, and gives the cloud an anvil shape. The water droplets combine to form larger droplets and freeze into ice particles. As they become heavier, they fall and melt, becoming rain. Sometimes the updraft is stronger that the droplets become too large to melt completely. These fall to the ground as hail. The falling rain and hail create downdrafts, which are usually present at the same time as updrafts. The presence of both is the culmination of the mature stage of the storm. This stage of the storm is also the one with the most turbulence, some of which can produce tornadoes, very strong winds and severe lightning.
In storms with no wind shear, the storm will “rain itself out” within 20 to 30 minutes. However, sometimes a strong wind shear will separate the downdraft and updraft, creating a super cell. The mature stage of these huge thunderstorms can last for several hours. These are the storms most often responsible for spawning deadly tornadoes.
– Dissipating Stage
The third stage, the dissipation stage, is the stage in which the storm basically ends. In the dissipating stage, the thunderstorm is dominated by the downdraft. The downdraft pushes down out of the storm, hits the ground and spreads out. This is known as a downburst. The cool air carried to the ground by the downdraft kills the warm moist air feeding the updraft, and it disappears. The thunderstorm is over.
