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A Multiscale Analysis of the 23-24 November 2004 Southeast United States Tornado Outbreak

A Multiscale Analysis of the 23-24 November 2004 Southeast United States Tornado Outbreak. Alicia C. Wasula. Event Summary. 23/1700 UTC – 24/1300 UTC (nocturnal) 80 Tornadoes (17 F2 or greater) 3 Fatalities / 38 Injuries 45% tornadoes close to Gulf coast (south of 32 N). Motivation.

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A Multiscale Analysis of the 23-24 November 2004 Southeast United States Tornado Outbreak

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  1. A Multiscale Analysis of the 23-24 November 2004 Southeast United States Tornado Outbreak Alicia C. Wasula

  2. Event Summary • 23/1700 UTC – 24/1300 UTC (nocturnal) • 80 Tornadoes (17 F2 or greater) • 3 Fatalities / 38 Injuries • 45% tornadoes close to Gulf coast (south of 32 N)

  3. Motivation • Examine tornado episode from synoptic/mesoscale perspective to look for similarities/differences to composite Gulf coast tornado episode

  4. CAPE vs. Shear for Cold Season Tornado Cases 0-2 km positive mean shear (x 10-3 s-1) Convective Available Potential Energy (CAPE, J/kg) Johns et al. 1993

  5. CAPE vs. Shear for Warm Season Tornado Cases 0-2 km positive mean shear (x 10-3 s-1) Convective Available Potential Energy (CAPE, J/kg) Johns et al. 1993

  6. Tornado Episode Composites • NCEP/NCAR 2.5x 2.5 Reanalysis dataset • All tornado episodes 1950-2001 • ‘Episode-relative’ composite • Grouped by start time: 0000-0600, 0600-1200, 1200-1800, 1800-0000 UTC • Will show 0600-1200 UTC only

  7. 200 hPa height (m), isotachs (m s-1) 500 hPa hgt (m), avor. (x 10-5 s-1), vort. adv. (x 10-10 s-2)

  8. 1000 hPa height (m), 1000-500 thck. (dam), 700 hPa RH (%) 850 hPa hgt (m), temp (C), temp. adv. (x 10-5 C s-1)

  9. 850 hPa winds, e (K), 850-500 lapse rate (C) 700 hPa height (m), vertical motion (x 10-3 hPa s-1)

  10. Summary: Composites • Strong signal in spite of large sample size: • ULJ entrance region at 200 hPa • Vigorous upstream trough at 500 hPa • Southwesterly LLJ at 850 hPa • Low-level e ridge • Surface composites show 1st tornado occurs: • At strongest T • On northern edge of moisture surge/southerly flow • Dew point anomalies > +8 C

  11. Case Study:24 November 2004

  12. http://www.spc.noaa.gov

  13. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 22 November 2004 0000 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  14. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 22 November 2004 1200 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  15. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 23 November 2004 0000 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  16. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 23 November 2004 1200 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  17. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 23 November 2004 1800 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  18. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 24 November 2004 0000 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  19. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 24 November 2004 0600 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  20. SLP, 1000-500 THCK 500 hPa HGHT, AVOR 24 November 2004 1200 UTC 850 hPa HGHT, e, ISOTACHS 200 hPa HGHT, ISOTACHS

  21. CAPE 1847 J/kg LI -7 0-6 km shear 38 kt 0-2 km shear 18 kt SWEAT 400 JAN 23/2100 UTC

  22. CAPE 1648 J/kg LI -6 0-6 km shear 58 kt 0-2 km shear 16 kt SWEAT 464 JAN 24/0000 UTC

  23. CAPE 81 J/kg LI 3 0-6 km shear 39 kt 0-2 km shear 22 kt SWEAT 225 JAN 24/1200 UTC

  24. CAPE 1794 J/kg LI -6 0-6 km shear 54 kt 0-2 km shear 4 kt SWEAT 279 LIX 24/0000 UTC

  25. CAPE 2087 J/kg LI -7 0-6 km shear 40 kt 0-2 km shear 12 kt SWEAT 332 LIX 24/0600 UTC

  26. CAPE 2986 J/kg LI -10 0-6 km shear 32 kt 0-2 km shear 10 kt SWEAT 513 LCH 23/1800 UTC

  27. CAPE 2412 J/kg LI -8 0-6 km shear 42 kt 0-2 km shear 9 kt SWEAT 353 LCH 24/0000 UTC

  28. Surface Analysis 24 November 2004 0000 UTC

  29. http://www.spc.noaa.gov

  30. http://www.spc.noaa.gov

  31. Surface Analysis 24 November 2004 0600 UTC

  32. http://www.spc.noaa.gov

  33.                                                                                                                                       <> IR 24 November 2004 0615 UTC http://locust.mmm.ucar.edu

  34. http://www.spc.noaa.gov

  35. Surface Analysis 24 November 2004 1200 UTC

  36. http://www.spc.noaa.gov

  37. Conclusions • Tornado episode occurred: • In presence of strong synoptic-scale forcing for ascent (in warm sector) • LLJ strength increased overnight • Surface winds stayed south or southeast as surface low rapidly deepened to the north • Ample moisture and instability

  38. Conclusions • Case study shows similarities to composite tornado episode • Strong shear/ULJ/LLJ • Deepening surface cyclone • Ample low-level moisture (esp. close to coast) • Surface winds ‘back’ with time ahead of surface low • Difference: • Mesoscale thermal gradient?

  39. Future Work • Question: • Did isallobaric effects help to keep flow in warm sector southerly/southeasterly and allow warm moist Gulf air to remain in place close to coast? • Why did LLJ increase in strength so rapidly? • Dynamically driven?

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