The Physical Environment
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Weather Systems

Severe Weather


Thunderstorm outflowFigure 8. 21 Thunderstorm outflow
(Source: NSSL - NOAA)

Thunderstorms have awed, intrigued, and inspired humans with their awesome force and power. There are two basic kinds of thunderstorms, air mass and severe. Air mass thunderstorms are usually created by convective uplift of warm, moist, and unstable air. Have you ever been surprised by a sudden downpour of thunderous rain on what was up to that point a pretty nice day? If so, it was probably an air mass thunderstorm. Air mass thunderstorms typically do not have very high winds, hail, or much lightning associated with them. Severe thunderstorms, however, do and may even spawn tornadoes. Severe thunderstorms tend to form along strong cold fronts where the air on either side is very different, the atmosphere is very unstable, and wind shear aloft is prevalent. Regardless of type, both kinds of thunderstorms tend to go through the same basic stages of development. We'll use the air mass thunderstorm to describe the stages of development here. [video icon Rotating supercell - video]

Stages of Thunderstorm Development

Cumulus stageFigure 8.22 Cumulus Stage
Image courtesy NSSL - NOAA
Click image to enlarge

The initial stage of development is called the cumulus stage. During this stage warm, moist, and unstable air is lifted from the surface. In the case of an air mass thunderstorm, the uplift mechanism is convection. As the air ascends, it cools and upon reaching its dew point temperature begins to condense into a cumulus cloud. Near the end of this stage precipitation forms.

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For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
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Michael Ritter (
Last revised 6/5/12

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