Chapter 18 thunderstorms.docx

Chapter 18 thunderstorms.docx - Chapter 18 thunderstorms I...

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Chapter 18: thunderstorms I. Thunderstorms also called cumulonimbus clouds, are tall, vertically developing clouds that produce lightning and thunder. They are important in the redistribution of moisture and heat, and are essential for agriculture and water resources. a. Severe thunderstorms normally require 4 elements for formation: i. A source of moisture ii. A conditionally unstable atmosphere iii. A mechanism to trigger the thunderstorms updraft, either through lifting or heating of the surface iv. Vertical wind shear, a rapid change in wind speed and/or wind direction with altitude. b. Thunderstorms organize differently depending on the lifting mechanism that triggers the storms, the vertical wind shear, and the degree of instability in the atmosphere. c. Destructive thunderstorms develop most often in an environment characterized by large conditional instability and strong vertical wind shear d. Lifting occurs along boundaries between airmasses. i. Front are most distinct and easily identifiable on weather maps in the cool season. e. Strong fronts are present, lifting occurs along the frontal boundary as the front advances and thunderstorms tend to organize along align with advancing front f. Thunderstorms that develop along subtle boundaries in the warm season often undergo a mode of self organization that eventually leads to the formation of what severe storm meteorologist call a mesoscale convective system g. In the cool season, when front are more distinct and the lifting is focused along fronts, very long lines of thunderstorms can develop along frontal boundaries, they are called frontal squall lines h. If winds increase rapidly with height ahead of a strong front of a less distinct boundary, thunderstorm triggered along that boundary may organize in yet another mode- violent storms called supercell thunderstorms i. Supercells can occur along a line or individually, but they always have their own individual circulations that are related to the storms rotation and the vertical shear in the atmosphere. They most often develop when strong winds are
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  • Spring '15
  • Thunderstorm, vertical wind shear, Supercell Thunderstorms, f. Thunderstorms

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