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Class #24: Monday October 26

Class #24: Monday October 26. The Extratropical or Midlatitude Cyclone continued. The story of an extratropical cyclone. Day 1, Sat., Nov. 8,1975: Low (Panhandle Hook) forms just NE of Amarillo Day 2, Sun., Nov. 9: Ship sails at 2 p.m.; Storm has matured to young adult stage

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Class #24: Monday October 26

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  1. Class #24: Monday October 26 The Extratropical or Midlatitude Cyclone continued Class #24: October 26

  2. The story of an extratropical cyclone • Day 1, Sat., Nov. 8,1975: Low (Panhandle Hook) forms just NE of Amarillo • Day 2, Sun., Nov. 9: Ship sails at 2 p.m.; Storm has matured to young adult stage • Day 3, Mon., Nov. 10: The storm is occluding. Ship sinks at 7:20 p.m. • Day 4, Tues., Nov. 11: The storm is dying • Subtract 7 from date to get Day # Class #24: October 26

  3. Sank on Day 3 Class #24: October 26 Fig. 10-1, p. 276

  4. Day 1 and Day 2 Class #24: October 26 Table 10-1a, p. 279

  5. Day 1 weather maps: Low forms NE of Amarillo, TX Class #24: October 26 Fig. 10-5, p. 280

  6. Birth to NW of Amarillo Class #24: October 26 Fig. 10-5a, p. 280

  7. Strong westerlies upstream Class #24: October 26 Fig. 10-5b, p. 280

  8. Low humidity, clear skies Class #24: October 26 Fig. 10-5c, p. 280

  9. Typical cyclone paths • Depend on topography • Depend on position of the polar front • Depend on upper level winds: • Extratropical cyclones move approximately with the 500mb wind at about half the speed Class #24: October 26 Fig. 10-6, p. 281

  10. Ingredients for a cyclone • Cyclone growth is called cyclogenesis • Cyclogenesis requires 3 ingredients: • Surface temperature gradients: a front • A strong jet stream: helps the low grow and the fronts intensify • Mountains or other surface boundaries (for example, a coastline along a warm ocean current • Cyclones get their energy in a process called baroclinic instability—related to horizontal temperature gradients and vertical wind shear Class #24: October 26

  11. Day 2: Young adult stage Class #24: October 26 Fig. 10-7, p. 285

  12. Note fronts, Low, and path. Ship sets sail at 2 p.m. Class #24: October 26 Fig. 10-7a, p. 285

  13. Note upper-level short-wave trough to west of surface Low Class #24: October 26 Fig. 10-7b, p. 285

  14. Satellite picture from 10:12 a.m.Note the comma shape of cloud Class #24: October 26 Fig. 10-7c, p. 285

  15. A close-up of last slide Class #24: October 26 Fig. 10-8, p. 286

  16. Back to the story • The cyclone moves very rapidly, steered by the upper-level winds at 500mb. • On Day 2 (Nov. 9) gale warnings were issued in the mid-afternoon for the next day (Monday, Day 3, Nov. 10) • Gale warnings are for winds up to 38 knots (44 mph), not typical, not too unusual • Ships take the northern, longer route Class #24: October 26

  17. Days 2 and 3 in Madison Wisconsin Class #24: October 26 Fig. 10-9, p. 287

  18. Day 2 Class #24: October 26 Fig. 10-10, p. 288

  19. Class #24: October 26 Fig. 10-10a, p. 288

  20. Class #24: October 26 Fig. 10-10b, p. 288

  21. Class #24: October 26 Fig. 10-10c, p. 288

  22. The story and the forecasts • At first the storm was expected to pass south of Lake Superior • A northern course over the lake would set the ships in northeasterly winds north of the low pressure center and a shorter fetch (distance over which the winds would blow) for smaller waves • By 10:39 p.m. on Day 2 the forecast changed. Class #24: October 26

  23. The new forecast at 10:39 p.m. on Day 2 • Winds of more than 40 knots (46 mph) on Lake Superior • Winds from the west and southwest • Waves of height 2.5 to 8 meters (8 to 15 feet) over Lake Superior • Over past 12 hours forecast wave heights doubled and forecast wind changed 180° • Shortly gale upgraded to storm warning Class #24: October 26

  24. What happened • A jet stream helped the storm to intensify, that is, for the surface pressure to decrease and the winds to increase • A jet stream helped to steer the storm to the northeast more quickly Class #24: October 26

  25. Surface pressure fallswhen there is divergenceof the wind in the columnof air above the low Class #24: October 26 Fig. 10-11, p. 289

  26. Class #24: October 26 Fig. 10-12, p. 290

  27. Jet stream (300mb) winds at 6p.m. on Day 2 Class #24: October 26 Fig. 10-13, p. 291

  28. Day 3, Day 4, and later Class #24: October 26 Table 10-1b, p. 279

  29. Day 3 Class #24: October 26 Fig. 10-14, p. 292

  30. Morning of Day 3: occlusion Class #24: October 26 Fig. 10-14a, p. 292

  31. Class #24: October 26 Fig. 10-14b, p. 292

  32. Class #24: October 26 Fig. 10-14c, p. 292

  33. Class #24: October 26 Fig. 10-16, p. 295

  34. Class #24: October 26 Fig. 10-17, p. 295

  35. Class #24: October 26 Box 10-3, p. 297

  36. Class #24: October 26 Box 10-3, p. 297

  37. Class #24: October 26 Box 10-3, p. 298

  38. Class #24: October 26 Box 10-3, p. 298

  39. Class #24: October 26 Box 10-3, p. 299

  40. Class #24: October 26 Box 10-3, p. 299

  41. Day 4: A dying storm Class #24: October 26 Fig. 10-18, p. 301

  42. Class #24: October 26 Fig. 10-18a, p. 301

  43. Class #24: October 26 Fig. 10-18b, p. 301

  44. Class #24: October 26 Fig. 10-18c, p. 301

  45. Class #24: October 26 Fig. 10-15, p. 294

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