Thunderstorms are a fact of life, especially in the spring and summer months. When the sun heats up the earth, and warm, moist air begins to lift into the atmosphere, there is potential for a storm to develop.
When the warm, moist air rises, it begins to cool, resulting in condensation, and the formation of a cumulus cloud. If the atmosphere is unstable to begin with, the cloud will form into a thunderstorm, causing the cloud to become a cumulonimbus cloud.
Cumulonimbus clouds are those dark threatening masses that announce the oncoming storm, and may include, and produce, strong winds, thunder, lightening, heavy rain, hail, and unfortunately, tornadoes.
An air mass thunderstorm is the storm that occurs late in the day, after a particularly hot afternoon. Surface heating produces a large number of convection currents in the atmosphere. This in turn produces the three stages that make up the storm. The first stage is the cumulus state when the cumulus clouds are formed. Warm air rises and forms puffy white clouds from the warm, moist air cooling. As long as the warm, humid air continues to rise through updrafts, the cloud will continue to develop and to retain heat, making it warmer than the air around it.
The second stage occurs when the updrafts reach their maximum altitude in the cloud, change their directions, and become downdrafts. This is the mature stage of the storm, and when the cloud becomes cumulonimbus. It takes on an anvil shape, turns dark and threatening, and contains heavy rain, thunder and lightening.
The final stage is the dissipation stage, when the rain slows, and the intensity begins to decrease. Warm, moist air is depleted, and the storm begins to break up. In a typical thunderstorm, the entire process may last no more than an hour.
Unfortunately, not all thunderstorms are of the short-lived variety. Severe thunderstorms move most often in an easterly direction, which tends to supply the storm with more warm, moist air. When a storm is supplied with more and more heat and humidity, the storm will keep growing and not dissipate. This is compounded by cold fronts, which push the storm along, caused by what is known as a mid-latitude cyclone, or a dry line.
Eventually, when there is no more moisture and heat to collect, usually after dark, when the air cools, the storm will break up. These are the long lasting, and far reaching storms that can dump a lot of rain over a larger area, and produce more severe wind and lightening damage.