11-tornadoes_v2011_v0

11-tornadoes_v2011_v0 - Chapter 11 Chapter Thunderstorms...

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Chapter 11 Chapter 11 Thunderstorms and Thunderstorms and Tornadoes Tornadoes
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Air mass thunderstorms are the most common and least Destructive, usually lasting for less than an hour. The cumulus stage begins when unstable air begins to rise and cool adiabatically to form fair weather cumulus clouds. The mature stage begins when precipitation starts to fall dragging air toward the surface as downdrafts form in areas of intense precipitation. As the cloud yields heavy precipitation, downdrafts occupy an increasing portion of the cloud base, the supply of additional water vapor is cut off, and the storm enters its dissipative stage .
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Cumulonimbus formation Santa Barbara, Feb 26, 2011 Possible Strong Downdrafts Upper level Divergence of air
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Severe thunderstorms have wind speeds exceeding 93 km/hr, have hailstones larger than 1.9 cm in diameter, or spawn tornadoes. They typically appear in groups with individual storms clustered together in mesoscale convective systems . Mesoscale convective systems that occur as linear bands are called squall lines .
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Mesoscale convective complexes (MCCs) appear as oval or roughly circular organized systems containing several thunderstorms and are self-propagating in that their individual cells often create downdrafts, leading to the formation of new, powerful cells nearby.
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Mesoscale Convective Systems: Squall lines Leading Edge Anvil Strong updrafts
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The precipitation from each thunderstorm cell creates its own downdraft, which is enhanced by the cooling of the air as the rain evaporates and consumes latent heat. Upon hitting the ground, the downdrafts spread outward and converge with warmer surrounding air forming an outflow boundary .
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New Convective cells formed as cold air descends from decaying storms Santa Barbara, Feb 26, 2011
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Squall line thunderstorms consist of individual storm cells arranged in a linear band about 500 km in length that form parallel
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11-tornadoes_v2011_v0 - Chapter 11 Chapter Thunderstorms...

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