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A thunderstorm formation begins with the Towering Cumulus Stage. The cumulus cloud grows upward of 20,000 feet or more. Air inside the blossoming cell experiences an upward pull with edges that produce turbulent eddies.
As the thunderstorm forms, it spreads. A diameter of 15 miles is the expected spread of typical thunderstorm. This stage of formation lasts about 10 minutes and produces little or no rain. However, occasional lightning occurs. -
This stage of maturity averages 10 to 20 minutes, but it could be longer depending upon the type of cell and the formation of the thunderstorm. At this stage, the storm will spill heavy rains, hail, frequent lightning, strong winds and possible tornado activity. The sky appears to be dark green or black.
There are four cell types capable of forming during this stage of maturity:
• Ordinary Cell
• Multi-cell Cluster
• Multi-cell Line
• Supercell Storm -
The Ordinary Cell stands alone. It is a single short-lived "pop-up" cell capable of wind gusts and hail. These characteristics are usually not severe in nature. However, given the right conditions and enough strength within the cell, more than one cell might form along with a possible microburst and weak tornados.
The Multi-cell Cluster is a group of ordinary cells gathered together in various stages of formation. One cell might be in the stage of formation at the same time that another cell reaches maturity and yet another is in the dissipating stage. The nature and formation of these thunderstorms means that they will continue rumbling for a longer time. These clusters are rainmakers, quickly producing tremendous amounts of water in a small area, causing flash flooding. -
The Multi-cell Line has the generic name of "squall line" with the ability to stretch for hundreds of miles. They will rumble and flash for hours as well as producing hail and damaging winds. New cells will reform at the leading edge of the line and rain, hail, wind and tornadoes follow behind the "front" line. Some cells can be quite strong and dangerous while others are unremarkable.
The leading edge of a squall line often provides the right conditions for tornado formation. Due to the nature of this line of storms, tornado activity usually is in the form of "straight line" wind damage. Sometimes the leading edge of a squall line has a shelf cloud--a low-hanging cloud shaped as an arc.
Finally, the Supercell Thunderstorm is a special kind of formation that has the ability to rumble for many hours. This thunderstorm is responsible for almost all tornadoes of significance in the United States. Hailstones larger than golf balls, flash floods and extreme winds make these supercells a strong force of nature. With 100-mile per hour (or more) winds, supercells are a phenomenal threat to life and property. -
The dissipating stage leaves the cloud tower without a supply of moist, warm air. The storm cannot preserve its character and fizzles away, leaving behind some misty rain and light, wispy winds.
Although the storm seems to be ending, this dissipating stage still displays vivid and dangerous lightning. Some thunderstorms also generate a rush of strong winds during this stage.
