9-24 - levels Potential instability(i.e dry air over warm...

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Squall lines Supercell Mesoscale Geography 1111 9/24/08 Midlatitude Severe Weather 1. Thunderstorms Types Formation and requirements Patterns of occurrence 2. Tornadoes Characteristics Formation and requirements Patterns of occurrence Thunderstorms
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Types of thunderstorms o Air mass thunderstorms o Severe thunderstorms Air mass thunderstorms o Most common type o Localized, fairly short lived o Least destructive o Occur within air masses o Uplift , rapid upward growth (10-45 mph)- 1 st stage o Precipitation starts, downdrafts, most intense rain, wind and lightening in 2 nd stage o Weak downdrafts dominate, storm dies out-3 rd stage Severe thunderstorms o Winds > 58mph o Hail >3/4” o Tornadoes o Meso-scale convective cluster—systems of thunderstorms o Supercell—single, huge thunderstorms o Squall lines—alone or ahead of cold fronts o Requirements High humidity through lower troposphere Uplift mechanism Wind shear (winds moving different directions at different
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Unformatted text preview: levels) Potential instability (i.e. dry air over warm, humid air) Thunderstorm occurrence • mT air masses • Florida has the most • E slope Rocky Mtns Tornadoes • Associated with severe thunderstorms • Rapidly rotating winds • Most—cyclonic direction • Travel about 30mph • Winds: 100-280mph • Sources of damage: o High winds o Abrupt pressure change • Requirements: o Severe thunderstorm associated with: Squall line/supercell along cold front Often enhanced in Great Plains by dry line Hurricane landfall o Vertical wind shear—induces rotation o Strong updraft, strong jet stream Tornado Occurrence • U.S. maximum—large region of relatively flat topography clash between cP and mT air masses in spring. • Seasonal peak occurs later in season farther north • Follows northward migration of jet stream...
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This note was uploaded on 01/17/2011 for the course GEOG 1111 taught by Professor Hopkins during the Fall '08 term at UGA.

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9-24 - levels Potential instability(i.e dry air over warm...

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