2005 National Severe Weather Workshop Paul Sirvatka April 20, 2004 Tornado Outbreak Nature Can Still Surprise… Paul L. Sirvatka Professor of Meteorology College of DuPage Glen Ellyn, IL

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

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

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

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

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

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

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

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

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

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

2005 National Severe Weather Workshop Paul Sirvatka Video from CBS-Chicago and NWS- LOT Jim Allsopp and Al Pietrycha

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

2005 National Severe Weather Workshop Paul Sirvatka Storm Reports  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  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 5 Supercells in Northeast Illinois

2005 National Severe Weather Workshop Paul Sirvatka 20Z Convective Outlook

2005 National Severe Weather Workshop Paul Sirvatka 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)  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 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  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 VAD Profile from LOT

2005 National Severe Weather Workshop Paul Sirvatka 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  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 21 Z Surface Map

2005 National Severe Weather Workshop Paul Sirvatka Visible Satellite Imagery

2005 National Severe Weather Workshop Paul Sirvatka Radar Review

2005 National Severe Weather Workshop Paul Sirvatka Watch Number :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 The result…?

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

2005 National Severe Weather Workshop Paul Sirvatka Convergent Rotation

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

2005 National Severe Weather Workshop Paul Sirvatka Mini-SupercellsMini-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)  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 22Z RUC Analysis (PIA ua and SPI sfc)

2005 National Severe Weather Workshop Paul Sirvatka 00Z DVN Sounding

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

2005 National Severe Weather Workshop Paul Sirvatka 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  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 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  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 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  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 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!  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 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?  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 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!!!!  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 AcknowledgementsAcknowledgements  Al Pietrycha and Jim Allsopp of the Chicago National Weather Service  Jon Davies Steve Drews Jim Krancic  College of DuPage Meteorology Staff  Al Pietrycha and Jim Allsopp of the Chicago National Weather Service  Jon Davies Steve Drews Jim Krancic  College of DuPage Meteorology Staff

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

2005 National Severe Weather Workshop Paul Sirvatka Amazing RFD

2005 National Severe Weather Workshop Paul Sirvatka LaSalle County Flyover

2005 National Severe Weather Workshop Paul Sirvatka Kankakee Tornado