Thunderstorms and Tornadoes

1. Chapter 10 Thunderstorms and Tornadoes

2. Thunderstorms • A storm containing lightning 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

3. Fig. 10-1, p. 275

4. Fig. 10-2, p. 276

5. Fig. 10-2a, p. 276

6. Fig. 10-2b, p. 276

7. Fig. 10-2c, p. 276

8. Stepped Art Fig. 10-2, p. 276

9. Fig. 10-3, p. 277

10. 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

11. Fig. 10-4, p. 278

12. Fig. 10-5, p. 278

13. Fig. 10-6, p. 279

14. Fig. 10-7, p. 279

15. Fig. 10-8, p. 280

16. Fig. 10-9, p. 280

17. Fig. 10-10, p. 281

18. Fig. 10-11, p. 281

19. Stepped Art Fig. 10-11, p. 281

20. Thunderstorms • Mutli-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, 10,000km2

21. Fig. 10-12, p. 282

22. Fig. 10-13, p. 282

23. Fig. 10-14, p. 282

24. Fig. 10-15, p. 283

25. Fig. 10-16, p. 283

26. 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

27. Fig. 10-17, p. 284

28. Fig. 10-18, p. 284

29. Fig. 10-19, p. 285

30. Fig. 10-20, p. 285

31. 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

32. Fig. 10-21, p. 286

33. Fig. 10-22, p. 287

34. 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

35. Fig. 10-23, p. 289

36. Fig. 10-24, p. 289

37. Thunderstorms • Lightning and Thunder • Lightning: discharge of electricity in mature storms (within cloud, cloud to cloud, cloud to ground) • Thunder: explosive expansion of air due to heat from lightning • Electrification of Clouds: graupel and hailstones fall through supercooled water, ice crystals become negatively charged • Upper cloud positive, bottom cloud negative

38. Fig. 10-25, p. 290

39. Fig. 10-26, p. 291

40. Fig. 10-27, p. 291

41. Thunderstorms • Types of lightning • Blue jets, red sprite, ELVES • The Lightning Stroke • Positive charge on ground, cloud to ground lightning • Stepped leader, ground stroke, forked lightning, ribbon lightning, bead lightning, corona discharge

42. Fig. 10-28, p. 292

43. Fig. 10-28a, p. 292

44. Fig. 10-28b, p. 292

45. Fig. 10-28c, p. 292

46. Fig. 10-29, p. 293

47. Fig. 10-30, p. 294

48. Fig. 10-31, p. 294

49. Fig. 10-32, p. 295

50. Thunderstorms • Lightning Detection and Suppression • Lightning direction finder detects radiowaves produced by lightning, spherics • National Lightning Detection Network • Suppression: seed clouds with aluminum • Observation: Apple tree • DO NOT seek shelter during a thunderstorm under an isolated tree.