Thunderstorms, regardless of whether or not they are severe, go through three stages during its life cycle. The towering cumulous stage is the first stage in which all air is moving upward in the developing storm. The scond stage, the mature stage, is the stage in which the updraft and downdraft co-exist at the same time. Finally, the third stage, the dissipating stage, is the stage in which the updraft has weakened and the downdraft overtakes the storm.
Thunderstorms are divided into four main categories:
True single cell storms are quite rare. Even the wekest storms often posess multicellular traits. Weak vertical wind shear limits the potential for convective scale organization. Storms developing in this enviornment are often short lived (20 to 30 minutes), and generally exist as a loosely organized group of cells. Severe storms that do develope in this weakly sheared enviornment are know as pulse storms. Severe weather is limites to brief downbursts, small-to-moderate size hail (generally less than one inch) and, infrequently, tornadoes. The "degree of predictability" of pulse storms is extremely low as forecasters are never quite sure which storm will produce severe weather and from which portion of that storm the severe events will occur.
The multicell cluster is the most common type of storm. It consists of a group of cells, moving along as one unit, with each cell in a different phase of the thunderstorm life cycle. As the cluster evolves, each cell taks its turn as the dominant cell. new cells tend to form at the upwind (usually western or southwestern) edge of the cluster. Mature cells are usually found at the center of the cluster, with dissipating cells at the downwind (usually eastern or northeastern) edge of the cluster. Although each cell lasts only about 20 minutes, the multicell cluster itself may persist for hours. These storms are usually more intense than single cell storms, but much weaker than Supercell storms. These storms can produce heavy rainfall, downbursts (wind speed up to 80 mph), moderate size hail (up to golfball size), and occasionally weak tornadoes. Severe weather tends to occur at the updraft/downdraft interface.
The squall line is a solid or broken line of thunderstorms with a continuous, well developed gustfront on the leading edge. Thus, updrafts and new updraft developement occur on the downwind(east) side, where the squall line is moving into unstable inflow air. Squall lines are common, especially in vertically sheared enviornments where the mid level winds are moderate to strong. Again, severe weather typically occurs at the updraft/downdraft interface - near the leading (or eastern) edge of the storm. The most common severe weather element in squall lines is the downburst, with dmamaging winds possible from the time of gustfront passage, into the period of heavy precipitation. Occasionally, an extremely strong downburst will accelerate a portion of the squall ahead of the rest of the line. THis produces a bow echo. Bow echoes are easily detected on radar, but are difficult to observe visually. Hail may occur with the rain. The heaviest rain and largest is usually adjacent to the updraft and near the leading edge of the squall line. Tornadoes, although rare, do occur with squall lines. Preferred locations for location for tornadic devfelopement is in cells just north of a break in the line or in the line's southernmost cell. Celss in these locations tend to behave more like supercells than typical squall lines.
Supercells are highly organized thinderstorms. They consist of one main updraft. The updraft can reach speeds of 150-175 mph. The main characteristic that sets the supercell thunderstorm apart from the rest is rotation. The rotating updraft is known as the mesocyclone. The mesocyclone helps the Supercell produce extreme severe weather events such as giant hail (more than 2 inches in diameter), strong downbursts of 80 mph, and tornadoes.
Visual Aspects of Supercell Thunderstorms
Upper-Level Features
Low-level Features
Below are the main differences between Wall Clouds and Shelf Clouds.
Wall Cloud:
