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Multiscale Analysis of Nov 2004 SE US Tornado Outbreak

Explore the Nov 2004 tornado outbreak in SE US from synoptic and mesoscale perspectives. Investigate the factors influencing tornado activity and compare with composite cases. Study includes composites, case study, and conclusions.

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Multiscale Analysis of Nov 2004 SE US 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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