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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 - PowerPoint PPT Presentation
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Class #24: Monday October 26
The Extratropical or Midlatitude Cyclone continued
1Class #24: October 26
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 2
Sank on Day 3
Class #24: October 26 3Fig. 10-1, p. 276
Day 1 and Day 2
Class #24: October 26 4Table 10-1a, p. 279
Day 1 weather maps: Low forms NE of Amarillo, TX
Class #24: October 26 5Fig. 10-5, p. 280
Birth to NW of Amarillo
Class #24: October 26 6Fig. 10-5a, p. 280
Strong westerlies upstream
Class #24: October 26 7Fig. 10-5b, p. 280
Low humidity, clear skies
Class #24: October 26 8Fig. 10-5c, p. 280
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 9Fig. 10-6, p. 281
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 10
Day 2: Young adult stage
Class #24: October 26 11Fig. 10-7, p. 285
Note fronts, Low, and path. Ship sets sail at 2 p.m.
Class #24: October 26 12Fig. 10-7a, p. 285
Note upper-level short-wave trough to west of surface Low
Class #24: October 26 13Fig. 10-7b, p. 285
Satellite picture from 10:12 a.m.Note the comma shape of cloud
Class #24: October 26 14Fig. 10-7c, p. 285
A close-up of last slide
Class #24: October 26 15Fig. 10-8, p. 286
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 16
Days 2 and 3 in Madison Wisconsin
Class #24: October 26 17Fig. 10-9, p. 287
Day 2
Class #24: October 26 18Fig. 10-10, p. 288
Fig. 10-10a, p. 28819Class #24: October 26
Fig. 10-10b, p. 28820Class #24: October 26
Fig. 10-10c, p. 28821Class #24: October 26
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 22
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 23
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 24
Surface pressure fallswhen there is divergenceof the wind in the columnof air above the low
Class #24: October 26 25Fig. 10-11, p. 289
Fig. 10-12, p. 29026Class #24: October 26
Jet stream (300mb) winds at 6p.m. on Day 2
Class #24: October 26 27Fig. 10-13, p. 291
Day 3, Day 4, and later
Class #24: October 26 28Table 10-1b, p. 279
Day 3
Class #24: October 26 29Fig. 10-14, p. 292
Morning of Day 3: occlusion
Class #24: October 26 30Fig. 10-14a, p. 292
Fig. 10-14b, p. 29231Class #24: October 26
Fig. 10-14c, p. 29232Class #24: October 26
Fig. 10-16, p. 29533Class #24: October 26
Fig. 10-17, p. 29534Class #24: October 26
Box 10-3, p. 29735Class #24: October 26
Box 10-3, p. 29736Class #24: October 26
Box 10-3, p. 29837Class #24: October 26
Box 10-3, p. 29838Class #24: October 26
Box 10-3, p. 29939Class #24: October 26
Box 10-3, p. 29940Class #24: October 26
Day 4: A dying storm
Class #24: October 26 41Fig. 10-18, p. 301
Fig. 10-18a, p. 30142Class #24: October 26
Fig. 10-18b, p. 30143Class #24: October 26
Fig. 10-18c, p. 30144Class #24: October 26
Fig. 10-15, p. 29445Class #24: October 26
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