1. Class #9: Monday, July 19 Thunderstorms and tornadoes Chapter 14 1Class #9, Monday, July 19, 2010

2. Fig. 14-CO, p. 370 2Class #9, Monday, July 19, 2010

3. Fig. 14-1, p. 372 3Class #9, Monday, July 19, 2010

4. Thunderstorms and Tornadoes Chapter 14 4Class #9, Monday, July 19, 2010

5. Thunderstorms A storm containing lightening and thunder; convective storms Severe thunderstorms: one of large hail, wind gusts greater than or equal to 50kts, or tornado Ordinary Cell Thunderstorms – Air-mass thunderstorms: limited wind sheer – Stages: cumulus, mature, dissipating – Entrainment, downdraft, gust front 5Class #9, Monday, July 19, 2010

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7. Fig. 14-2, p. 373 7Class #9, Monday, July 19, 2010

8. Fig. 14-2, p. 373 8Class #9, Monday, July 19, 2010

9. Fig. 14-2, p. 373 9Class #9, Monday, July 19, 2010

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11. Fig. 14-4, p. 375 11Class #9, Monday, July 19, 2010

12. Thunderstorms  Multi-cell Thunderstorms Thunderstorms that contain a number of convection cells, each in a different stage of development, moderate to strong wind shear; tilt, over shooting top Gust Front: leading edge of the cold air out-flowing air; shelf cloud, roll cloud, outflow boundary Micro-bursts: localized downdraft that hits the ground and spreads horizontally in a radial burst of wind; wind shear, virga 12Class #9, Monday, July 19, 2010

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14. Fig. 14-6, p. 376 14Class #9, Monday, July 19, 2010

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18. Thunderstorms Multi-cell Thunderstorms – Squall-line thunderstorms; line of multi-cell thunderstorms, pre-frontal squall-line, derecho – Meso-scale Convective Complex: a number of individual multi-cell thunderstorms grow in size and organize into a large circular convective weather system; summer, 10,000km 2 18Class #9, Monday, July 19, 2010

19. Fig. 14-10, p. 378 19Class #9, Monday, July 19, 2010

20. Fig. 14-11, p. 378 20Class #9, Monday, July 19, 2010

21. Stepped Art Fig. 14-11, p. 378 21Class #9, Monday, July 19, 2010

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28. Thunderstorms  Supercell thunderstorms Large, long-lasting thunderstorm with a single rotating updraft Strong vertical wind shear Outflow never undercuts updraft Classic, high precipitation and low precipitation supercells Cap and convective instability Rain free base, low-level jet Surface, 850mb, 700mb, 500mb, 300mb conditions 28Class #9, Monday, July 19, 2010

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34. Fig. 14-23, p. 384 34Class #9, Monday, July 19, 2010

35. Thunderstorms  Thunderstorms and the Dryline Sharp, horizontal change in moisture Thunderstorms form just east of dryline cP, mT, cT  Floods and Flash Floods Flash floods rise rapidly with little or no advance warning; many times caused by stalled or slow thunderstorm Large floods can be created by training of storm systems, Great Flood of 1993 35Class #9, Monday, July 19, 2010

36. Fig. 1, p. 386 36Class #9, Monday, July 19, 2010

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38. Thunderstorms Topic: Big Thompson Canyon – July 31, 1976, 12 inches of rain in 4 hours created a flood associated with $35.5million in damage and 135 deaths Distribution of Thunderstorms – Most frequent Florida, Gulf Coast, Central Plains – Fewest Pacific coast and Interior valleys – Most frequent hail Central Plains 38Class #9, Monday, July 19, 2010

39. Fig. 14-25, p. 387 39Class #9, Monday, July 19, 2010

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42. Thunderstorms Lightening and Thunder – Lightening: discharge of electricity in mature storms (within cloud, cloud to cloud, cloud to ground) – Thunder: explosive expansion of air due to heat from lightening – Electrification of Clouds: graupel and hailstones fall through supercooled water, ice crystals become negatively charged – Upper cloud positive, bottom cloud negative 42Class #9, Monday, July 19, 2010

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44. Fig. 2, p. 390 44Class #9, Monday, July 19, 2010

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47. Thunderstorms Observations: Elves – Blue jets, red sprite, ELVES The Lightening Stroke – Positive charge on ground, cloud to ground lightening – Stepped leader, ground stroke, forked lightening, ribbon lightening, bead lightening, corona discharge 47Class #9, Monday, July 19, 2010

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49. Thunderstorms Observation: Apple tree – DO NOT seek shelter during a thunderstorm under an isolated tree. Lightening Detection and Suppression – Lightening direction finder detects radiowaves produced by lightening, spherics – National Lightening Detection Network – Suppression: seed clouds with aluminum 49Class #9, Monday, July 19, 2010

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51. Fig. 14-32, p. 392 51Class #9, Monday, July 19, 2010

52. Fig. 14-33, p. 393 52Class #9, Monday, July 19, 2010

53. Fig. 14-34, p. 393 53Class #9, Monday, July 19, 2010

54. Fig. 14-35, p. 394 54Class #9, Monday, July 19, 2010

55. Fig. 14-36, p. 394 55Class #9, Monday, July 19, 2010

56. Fig. 3, p. 395 56Class #9, Monday, July 19, 2010

57. Fig. 14-37, p. 396 57Class #9, Monday, July 19, 2010

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59. Tornadoes Rapidly rotating column of air that blows around a small area of intense low pressure with a circulation that reaches the ground. Tornado life cycle – Organizing, mature, shrinking, decay stage Tornado outbreaks – Families, super outbreak 59Class #9, Monday, July 19, 2010

60. Tornadoes  Tornado Occurrence US experiences most tornadoes Tornado Alley (warm, humid surface; cold dry air aloft) Highest spring, lowest winter  Tornado winds Measurement based upon damage after storm or Doppler radar For southwest approaching storms, winds strongest in the northeast of the storm, 220 kts maximum Multi-vortex tornados 60Class #9, Monday, July 19, 2010

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65. Tornadoes Seeking shelter – Basement or small, interior room on ground floor – Indoor vs. outdoor pressure The Fujita Scale – Based upon the damage created by a storm – F0 weakest, F5 strongest – Enhanced Fujita Scale 65Class #9, Monday, July 19, 2010

66. Tornadic Formation Basic requirements are an intense thunderstorm, conditional instability, and strong vertical wind shear Supercell Tornadoes – Wind sheer causes spinning vortex tube that is pulled into thunderstorm by the updraft – Mesocyclone, BWER, rear flank downdraft, vertical stretching, funnel cloud, rotating cloud, wall cloud 66Class #9, Monday, July 19, 2010

67. Table 14-1, p. 399 67Class #9, Monday, July 19, 2010

68. Table 14-2, p. 400 68Class #9, Monday, July 19, 2010

69. Table 14-3, p. 400 69Class #9, Monday, July 19, 2010

70. Fig. 14-42, p. 400 70Class #9, Monday, July 19, 2010

71. Fig. 14-43, p. 401 71Class #9, Monday, July 19, 2010

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75. Stepped Art Fig. 14-46, p. 402 75Class #9, Monday, July 19, 2010

76. Tornadic Formation Nonsupercell Tornadoes – Gustnadoes – Land spout – Cold-air funnels 76Class #9, Monday, July 19, 2010

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79. Severe Weather and Doppler Radar Doppler radar measures the speed of precipitation toward and away radar unit Two Doppler radars can provide a 3D view TVS, Doppler lidar NEXRAD 79Class #9, Monday, July 19, 2010

80. Fig. 14-49, p. 405 80Class #9, Monday, July 19, 2010

81. Fig. 14-50, p. 405 81Class #9, Monday, July 19, 2010

82. Fig. 14-51, p. 406 82Class #9, Monday, July 19, 2010

83. Waterspouts Rotating column of air that is connected to a cumuliform cloud over a large body of water Tornadic waterspout 83Class #9, Monday, July 19, 2010

84. Fig. 14-52, p. 409 84Class #9, Monday, July 19, 2010