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Severe Weather 13-2

Severe Weather 13-2. Supercells. Cold fronts often are accompanied by high pools of cold air The strength of the updrafts and downdrafts intensify Self-sustaining Intense rotating updrafts Can last for hours, have updrafts up to 240 mph. Lightning.

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Severe Weather 13-2

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  1. Severe Weather 13-2

  2. Supercells • Cold fronts often are accompanied by high pools of cold air • The strength of the updrafts and downdrafts intensify • Self-sustaining • Intense rotating updrafts • Can last for hours, have updrafts up to 240 mph

  3. Lightning • Friction between updrafts and downdrafts separate electrons from their atoms • The clouds become charged opposite of the charge of the ground • Stepped leader (channel of charged air) gets near to the ground • Return stroke reaches up to touch the stepped leader • Lights up the channel with about 100 million volts of electricity • Heats the air to about 30,000oC • Thunder – superheated air expands and contracts

  4. Wind • Downbursts • Violent downdrafts concentrated in a local area • Speeds of more than 160 km/h • Microbursts and macrobursts • Downbursts are classified depending on the size of the area affected • Macrobursts can cause path of destruction 5 km wide with wind speeds of 200km/h (30 minutes) • Microbursts can cause path of destruction less than 3 km wide with wind speeds of 250 km/h (10 minutes)

  5. Tornadoes • A tornado is a violently rotating column of air in contact with the ground and out from a cumulonimbus cloud. • Tornadoes are capable of inflicting extreme damage.

  6. Tornadoes can be categorized as "weak", "strong", and "violent"; with weak tornadoes often having a thin, rope-like appearance. • About 7 in 10 tornadoes are weak, with rotating wind speeds no greater than about 110 MPH. • The typical strong tornado often has a "classic" funnel-shaped cloud associated with the whirling updraft. Rotating wind speeds vary from 110 to 200 MPH.

  7. Nearly 3 in 10 tornadoes are strong, such as this twister on the plains of North Dakota

  8. Less than 2 percent of all tornadoes reach the 200+ MPH violent category. • Most violent tornadoes only produce home-leveling damage within a very small area • Less than 5 percent of the 5,000 affected homes in Wichita Falls, Texas were leveled by this massive 1979 tornado.

  9. Wall Cloud: a localized lowering from a rain-free base. Often produce tornadoes

  10. A Tornado Develops

  11. Fujita Tornado Intensity Scale The Fujita scale, or F scale, categorizes tornado severity based on observed damage to man-made structures and on recorded wind speeds. F0: Gale tornado (40-72 mph); light damage. Some damage to chimneys; break branches off trees; push over shallow-rooted trees; damage to sign boards.

  12. F1: Moderate tornado (73-112 mph); moderate damage. The lower limit is the beginning of hurricane wind speed; peel surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads.

  13. F2: Significant tornado (113-157 mph); considerable damage. roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light-object missiles generated.

  14. F3: Severe tornado (158-206 mph); Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown.

  15. F4: Devastating tornado (207-260 mph); Devastating damage. Well- constructed houses leveled; structure with weak foundation blown off some distance; cars thrown and large missiles generated.

  16. F5: Incredible tornado (261-318 mph); Incredible damage. Strong frame houses lifted off foundations and carried considerable distance to disintegrate; automobile sized missiles fly through the air in excess of 100 yards; trees debarked; incredible phenomena will occur.

  17. Some Significant Tornadoes • Oklahoma City, OK, May 3, 1999: On Monday evening, May 3, a long track F5, violent tornado traveled from near Chickasha, Oklahoma, to just east of Oklahoma City, Oklahoma. Along its path this tornado produced areas of F5 damage to both rural sections of central Oklahoma as well as densely populated areas of Oklahoma City and its suburbs. In the wake of this single tornado, there were 42 people left dead, several hundred injured and over 1 billion dollars in damage.

  18. Deadliest Tornadoes • The Tri-State Tornado Outbreak of March 18, 1925 killed 689 people in Missouri, Illinois and Indiana. Murphrysboro, Ill., had 234 of those deaths, and West Frankfort, Ill., had 127. • Other deadly tornadoes include the May 6, 1840 tornado which killed 317 people in Natchez, Mississippi; the May 27, 1896, tornado which killed 255 in St. Louis, Missouri. Tornadoes on successive days in 1936 killed 216 people in Tupelo, Mississippi, on April 5; and 203 people in Gainesville, Georgia, on April 6.

  19. Biggest, Costliest Outbreaks • The April 3-4, 1974 Super Outbreak was the largest known outbreak, with 148 tornadoes in 11 states, killing 315 people, injuring more than 5,300 and causing $600 million in damages. Alabama, Kentucky and Ohio were the states hardest hit. Perhaps the most notable tornado of the outbreak was one which touched down southwest of Xenia, Ohio. The violent tornado destroyed half the town, killing 34 and causing property damages of more than $100 million.

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