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The Life Cycle of an Extratropical Cyclone: From Formation to Dissipation

This class details the intriguing progression of an extratropical cyclone that took place in November 1975. Beginning with the formation of a low-pressure system northeast of Amarillo, the storm rapidly developed through various stages, eventually reaching a mature young adult phase. As it occluded and struggled to maintain intensity, gale warnings led to significant weather changes over Lake Superior. Observing the cyclone's evolution highlights the critical factors involved in cyclogenesis, including temperature gradients, jet streams, and surface boundaries.

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The Life Cycle of an Extratropical Cyclone: From Formation to Dissipation

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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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