April 20 2004 Tornado Outbreak Nature Can Still

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

Event Overview Ø April 20, 2004 in Iowa, Illinois and Indiana Ø 30 Tornadoes Ø 8 Deaths in Utica IL Ø Milestone Tavern Collapsed Ø 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

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

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

20 Z Convective Outlook 2005 National Severe Weather Workshop Paul Sirvatka

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

Favorable for Severe Ø Incredible low-level Ø Ø Ø shear 0 -1 KM 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 Ø CAPE was limited Ø Rain-cooled air in spring almost always kills the threat of surfaced-based severe in NE IL Ø Initiation mechanism in warm sector was uncertain Ø Despite strong SRH in 01 km, it won’t be realized if storms are elevated 2005 National Severe Weather Workshop Paul Sirvatka

2005 National Severe Weather Workshop Paul Sirvatka 21 Z Surface Map

Visible Satellite Imagery 2005 National Severe Weather Workshop Paul Sirvatka

Radar Review 2005 National Severe Weather Workshop Paul Sirvatka

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

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

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

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

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

Summary of April 20 th Events Ø Forecasters missed the event in terms of surface-based convection Ø 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! Ø Warnings were issued Ø Ø 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? Ø We need more skill in weather forecasting - models are not 100% reliable Ø Spring warm fronts can produce very dangerous weather events Ø Lift, moisture, instability, wind shear: what is missing? Watch for the last ingredient to show up! Ø High CAPE is overrated! 2005 National Severe Weather Workshop Paul Sirvatka

Questions to Answer Ø Why did the models miss the CAPE so badly? Should forecasters have anticipated the miss? Ø Why did the air clear north of the early spring warm front? Ø 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… Ø Supercells come in many shapes and sizes but they are all dangerous Ø Be prepared in all circumstances Ø Meteorology can always find ways to surprise us and teach us Ø Tornadoes are cool!!!! 2005 National Severe Weather Workshop Paul Sirvatka

Acknowledgements Ø Al Pietrycha and Jim Allsopp of the Chicago National Weather Service Ø Jon Davies Steve Drews Jim Krancic Ø College of Du. Page Meteorology Staff 2005 National Severe Weather Workshop Paul Sirvatka