There are three types of thunderstorms:

Photos of the Single Cell, Multi-Cell Cluster and Multi-Cell Squall Line were taken by NSSL
The photo of the Supercell was taken by Howie Bluestein
The photos were taken from the storm spotters guide at the University of Illinois' Daily Planet web page.

Although the natural environment does not fall into three distinct categories, we break them down to help illustrate significant differences. The differences arise because of varying atmospheric profiles, especially those concerned with vertical shear, defined as the change in wind velocity (speed or direction) with height, or.

The air mass thunderstorm is a common and usually non-severe phenomenon that forms away from frontal systems or other synoptic-scale disturbances. They form where moist and unstable conditions exist in the atmosphere. Air mass thunderstorms are usually produced in areas of very little vertical shear. As a result, the threat for severe is small. When they do reach severe limits, the thunderstorms may produce brief high winds or hail which develop because of high instability. These storms are know as pulse severe storms. Although several storm cells can develop, each individual cell lasts about 30-60 minutes and has three stages.

Cumulus Stage: Graph , Picture

Mature Stage: Graph , Picture

Dissipating Stage: Graph , Picture

(Pics and Graphs from Steve Davis WSFO Milwaukee/Sullivan)

As wind shear organizes the convection, new thunderstorms form as a result of parent thunderstorm outflows converging with warm, moist inflow creating new updrafts. Multicell storms can form in a line known as a squall line, where continuous updrafts form along the leading edge of the outflow, or gust front. Multicell clusters indicate new updrafts are forming where the low-level convergence is strongest, usually at the right, or right-rear flank of existing cells.

Thunderstorms that organize in response to synoptic scale forcing usually need:

- warm, moist air at low levels
- cool, dry air at upper levels
- upper-level divergence (above 500mb)
- a synoptic scale disturbance

In these conditions, thunderstorm formation is probable. Synoptic scale vertical motions tend to create favorable conditions for thunderstorms, but thunderstorm initiation is usually a result of mesoscale forcing. Increasingly favorable vertical wind profiles may lead to a greater possibility of supercell development rather than multicell storms. The development of squall lines, or more commonly storm clusters, when thunderstorms do develop is virtually guaranteed in association with synoptic scale forcing.

Multicellular storms consist of a series of evolving cells. At low levels, cooler air diverging from the downdraft intersects the inflowing air along a gust front, creating a region of strong low- level convergence favorable for new updrafts. It is the presence of vertical wind shear that results in the "tilting" of the updraft and downdraft. Because of the tilting, the less buoyant downdraft air will not destroy the updraft and hence deprive itself up supersaturated updraft air. In any case, the movement of multicell storms systems is determined by combining the new cell development with the mean winds. Each individual cell typically moves with the mean winds, while new cells develop where the inflow meets the outflow, hence, in the region of strongest surface, or low-level, convergence.

Supercells are the most powerful thunderstorms. By their definition, supercells are always severe. Supercells are responsible for a disproportionate amount of damage and casualties. The most significant difference arises from the presence of a rotating updraft, or mesocyclone. These features insure the longevity of a thunderstorm by allowing the flanking line to enhance the inflow into one main updraft, rather than helping create new updraft centers. The combination of rotation and longevity increase the chances for the development of strong or violent tornadoes.

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