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April 20, 2004 Tornado Outbreak

Nature Can Still Surprise…. April 20, 2004 Tornado Outbreak. Paul L. Sirvatka Professor of Meteorology College of DuPage Glen Ellyn, IL. Event Overview. April 20, 2004 in Iowa, Illinois and Indiana 30 Tornadoes 8 Deaths in Utica IL Milestone Tavern Collapsed Sought Safer Shelter.

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April 20, 2004 Tornado Outbreak

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  1. Nature Can Still Surprise… April 20, 2004Tornado Outbreak Paul L. SirvatkaProfessor of MeteorologyCollege of DuPageGlen Ellyn, IL 2005 National Severe Weather Workshop Paul Sirvatka

  2. Event Overview • April 20, 2004 in Iowa, Illinois and Indiana • 30 Tornadoes • 8 Deaths in Utica IL • Milestone Tavern Collapsed • Sought Safer Shelter 2005 National Severe Weather Workshop Paul Sirvatka

  3. Northeast Illinois 2005 National Severe Weather Workshop Paul Sirvatka

  4. Photo courtesy of Jim Krancic 2005 National Severe Weather Workshop Paul Sirvatka

  5. Photo courtesy of Jim Krancic 2005 National Severe Weather Workshop Paul Sirvatka

  6. Photo courtesy of Jim Krancic 2005 National Severe Weather Workshop Paul Sirvatka

  7. Photo courtesy of Jim Krancic 2005 National Severe Weather Workshop Paul Sirvatka

  8. Photo courtesy of Jim Krancic 2005 National Severe Weather Workshop Paul Sirvatka

  9. Granville, IL Photos courtesy of Steve Drews 2005 National Severe Weather Workshop Paul Sirvatka

  10. Granville, IL Photos courtesy of Steve Drews 2005 National Severe Weather Workshop Paul Sirvatka

  11. Utica, IL Photos courtesy of Steve Drews 2005 National Severe Weather Workshop Paul Sirvatka

  12. F -3 Damage to Milestone Tavern Photos courtesy of Steve Drews 2005 National Severe Weather Workshop Paul Sirvatka

  13. Video from CBS-Chicago and NWS- LOTJim Allsopp and Al Pietrycha 2005 National Severe Weather Workshop Paul Sirvatka

  14. Synoptic Scale Set-up 2005 National Severe Weather Workshop Paul Sirvatka

  15. Storm Reports 4-20-04 • 53 tornado reports nationwide • Very few hail reports in Northern Illinois • Largest hail occurred in warm sector but there was tennis ball hail with the LaSalle County Storm 2005 National Severe Weather Workshop Paul Sirvatka

  16. 5 Supercells in Northeast Illinois 2005 National Severe Weather Workshop Paul Sirvatka

  17. 20Z Convective Outlook 2005 National Severe Weather Workshop Paul Sirvatka

  18. Why the Miss? • Completely missed the forecast instability • Pattern recognition was incorrect • Stratiform rain and clouds cleared in a narrow band along warm front • All numerical guidance was poor (RUC and ETA) 2005 National Severe Weather Workshop Paul Sirvatka

  19. Favorable for Severe • Incredible low-level shear 0-1KM north of warm front • Clearing in narrow zone north of front • Sufficient moisture • Favorable storm motion with respect to front motion 2005 National Severe Weather Workshop Paul Sirvatka

  20. VAD Profile from LOT 2005 National Severe Weather Workshop Paul Sirvatka

  21. Unfavorable for Severe • CAPE was limited • Rain-cooled air in spring almost always kills the threat of surfaced-based severe in NE IL • Initiation mechanism in warm sector was uncertain • Despite strong SRH in 0-1km, it won’t be realized if storms are elevated 2005 National Severe Weather Workshop Paul Sirvatka

  22. 21 Z Surface Map 2005 National Severe Weather Workshop Paul Sirvatka

  23. Visible Satellite Imagery 2005 National Severe Weather Workshop Paul Sirvatka

  24. Radar Review 2005 National Severe Weather Workshop Paul Sirvatka

  25. Watch Number 95 - 5:40 PM CDT DISCUSSION...FAVORABLE SHEAR PROFILES ON NWD MOVING WARM FRONT FOR TORNADIC SUPERCELLS. STORMS WILL CONTINUE TO DEVELOP AS THE WARM FRONT SHIFTS NWD INTO NRN IL/IND. 2005 National Severe Weather Workshop Paul Sirvatka

  26. The result…? 2005 National Severe Weather Workshop Paul Sirvatka

  27. Storms Spun like Tops! 2005 National Severe Weather Workshop Paul Sirvatka

  28. Convergent Rotation 2005 National Severe Weather Workshop Paul Sirvatka

  29. Mini-Supercells TBSS (Three-body Scatter Spike) 2005 National Severe Weather Workshop Paul Sirvatka

  30. Mini-Supercells • Tornadic cases have a great deal of CAPE below 500mb • Lower total CAPE and lower EL • Significant shear over the depth of the storm (30-35k feet) 2005 National Severe Weather Workshop Paul Sirvatka

  31. 22Z RUC Analysis (PIA ua and SPI sfc) 2005 National Severe Weather Workshop Paul Sirvatka

  32. 00Z DVN Sounding 2005 National Severe Weather Workshop Paul Sirvatka

  33. 100 mb vs. 50 mb MLCAPE 2005 National Severe Weather Workshop Paul Sirvatka

  34. Summary of April 20th Events • Warm front provided source of lift and additional vorticity • Low LCL’s, high helicity and adequate moisture and shear • CAPE appeared to be lacking but was more than sufficient with limited sunshine • Speed of storms and front matched, allowing for storms to stay in “sweet zone” for a long period of time • Position of 850mb warm front 2005 National Severe Weather Workshop Paul Sirvatka

  35. Summary of April 20th Events • Forecasters missed the event in terms of surface-based convection • The response to what was actually happening was quick, decisive and showed a good state of readiness - situational awareness was strong 2005 National Severe Weather Workshop Paul Sirvatka

  36. 100% POD! • Warnings were issued prior to all tornadoes • FAR = .58 CSI = .42 • Average lead time is 15.6 minutes • Utica tornado had a lead time of 26 minutes • Excellent spotter reports from chasers, spotters and law enforcement officers 2005 National Severe Weather Workshop Paul Sirvatka

  37. So What Can We Learn? • We need more skill in weather forecasting - models are not 100% reliable • Spring warm fronts can produce very dangerous weather events • Lift, moisture, instability, wind shear: what is missing? Watch for the last ingredient to show up! • High CAPE is overrated! 2005 National Severe Weather Workshop Paul Sirvatka

  38. Questions to Answer • Why did the models miss the CAPE so badly? Should forecasters have anticipated the miss? • Why did the air clear north of the early spring warm front? • Would we anticipate this event in the future? 2005 National Severe Weather Workshop Paul Sirvatka

  39. The “No-duh” info that we need to hear over and over… • Supercells come in many shapes and sizes but they are all dangerous • Be prepared in all circumstances • Meteorology can always find ways to surprise us and teach us • Tornadoes are cool!!!! 2005 National Severe Weather Workshop Paul Sirvatka

  40. Acknowledgements • Al Pietrycha and Jim Allsopp of theChicago National Weather Service • Jon DaviesSteve DrewsJim Krancic • College of DuPage Meteorology Staff 2005 National Severe Weather Workshop Paul Sirvatka

  41. Close-up of Joliet Tornadic Storm 2005 National Severe Weather Workshop Paul Sirvatka

  42. Amazing RFD 2005 National Severe Weather Workshop Paul Sirvatka

  43. LaSalle County Flyover 2005 National Severe Weather Workshop Paul Sirvatka

  44. Kankakee Tornado 2005 National Severe Weather Workshop Paul Sirvatka

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