Utility of 0-3 km Bulk Shear Vectors as a Predictor for Quasi-Linear Convective System (QLCS) Tornadoes

1
Utility of 0-3 km Bulk Shear Vectors as a
Predictor for Quasi-Linear Convective System
(QLCS) Tornadoes
McKenna W. Stanford University of South
Alabama Meteorology Weather-Ready Nation National
Weather Service, Springfield, MO David Gaede,
Jason Schaumann, John Gagan
NOAAs National Weather Service
2
Outline

• Introduction/Objectives
• Background
• Methodology
• Criteria Recognition
• Results
• Statistical Analyses
• Application to Protection of Life Property
• Next Steps
• Summary
• Acknowledgements
• References

3
Introduction/Objectives

• McKenna W. Stanford
• University of South Alabama
• Meteorology, Major
• Mathematics, Minor
• National Weather Service, Springfield, MO WFO
• Weather-Ready Nation
• Personal Motivation My interest in severe
  convective storms and aspirations to investigate
  them and improve warning strategies for
  destructive events aided in my selection of this
  project.
• Objective Statistically verify identified
  predictors for QLCS tornadoes and improve Tornado
  Warning lead times in order to satisfy NOAAs
  objective for reduced loss of life, property,
  and disruption from high-impact events.

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Co-Collaborators

• Contributors to this project included
• David Gaede, Mentor, Science Operations Officer
• Jason Schaumann, Co-Mentor, Senior Forecaster
• John Gagan, Co-Mentor, Senior Forecaster

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QLCS Background

• Quasi-Linear Convective Systems (QLCSs)
• Produce large swaths of wind damage
• Descending rear-inflow jets (RIJs)
• Embedded microbursts macrobursts
• Localized swaths of (E)F-0 to (E)F-1 wind damage
  can occur
• Can contain embedded tornadoes
• Usually (E)F-0 to (E)F-1 damage
• Documented damage intensity up to (E)F-4

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QLCS vs. Supercell
Moore, OK KTLX 20 May 2013
Sunset Hills, MO KLSX 31 December 2010
Photo Courtesy of NWS St. Louis
Photo Courtesy of FEMA
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Motivation for Research

• Much research has been conducted involving
  environments and physical processes related to
  supercell tornadoes versus those of QLCSs
• Warning skill and lead times for QLCS tornadoes
  remains poor
• Most warning decision forecasters issue Tornado
  Warnings after mesovortex development
• Recent studies have shown the average lead time
  for this technique is only around 5 minutes
• Can also result in high False Alarm Rates (FAR) -
  crying wolf

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Additional Disadvantages to Current Tornado
Warning Strategies

• Due to the quick nature of mesovortex genesis,
  mesovoritices can form in between radar volume
  scans
• Radar beam will overshoot features at distances
  greater than 40 nautical miles (nm) from the
  radar

• Where does the 0.5 tilt reach 1 km AGL?
• How do we resolve these issues?

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Alternative Methodology to Anticipate QLCS
Tornadogenesis

• Schaumann and Przybylinski (2012) examined
  several QLCS events to identify three co-existing
  ingredients, both physical properties and radar
  characteristics, that present an increased
  likelihood for mesovortex genesis and rapid
  intensification
• (1) A portion of the QLCS in which the system
  cold pool and ambient low-level shear are
  nearly balanced or slightly shear dominant AND
• (2) The 0-3 km line-normal bulk shear magnitudes
  are equal to or greater than 15 m s-1 (30 knots)
  AND
• (3) A rear-inflow jet (RIJ) or enhanced outflow
  causes a surge or bow in the line
• The intent of this study is to verify this
  three-ingredients method and provide statistical
  significance to its practice

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Methodology Case Selection

• Period of study 2005-2011
• 31 cases
• Warm cold season

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Mesovortex Identification
GR2Analyst Software
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Surge Identification
Surge on rear flank of leading convective line
Surge on forward flank of leading convective line
GR2Analyst Software
GR2Analyst Software
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Determining Balance Regime
0.5 Z
0-3 km Bulk Shear Vectors

• Five Different Regimes
• Shear Dominant
• Slightly Shear Dominant
• Balanced
• Slightly Cold Pool Dominant
• Cold Pool Dominant

Shear Dominant
Cold Pool Dominant
Balanced
Balanced Slightly Shear Dominant are regimes
necessary in three-ingredients method
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Determining 0-3 km Bulk Shear Vector Magnitude
Direction

4-Panels Courtesy of Chad Gravelle, Ph.D.
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Determining 0-3 km Line-Normal Shear Magnitude
Updraft-Downdraft Convergence Zone (UDCZ)
?u
T
?u sin(?)m
m
?u line-normal magnitude of 0-3 km bulk shear T
angle between convective line and 0-3 km bulk
shear vector m magnitude of 0-3 km bulk shear
vector
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Performance of Three-Ingredients Method

• 67 Mesovortices
• 64 Non-Mesovortex Surges
• 52 of identified mesovorticies produced at least
  one report of winds 50 knots and/or a tornado
• Verification for three-ingredients method
• Probability of Detection (POD) 79
• False Alarm Rate (FAR) 23

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0-3 km Bulk and Line-Normal Shear for all
Mesovortices
Mean Bulk Shear 37 kts
Mean Line-Normal Shear 33 kts
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0-3 km Line-Normal Shear for all Mesovortices
Non-Mesovortex Surges
Mean Line-Normal Shear for Non-Mesovortex Surges
26 kts
Mean Line-Normal Shear for Mesovortices 33 kts
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Three-Ingredients Method for all Mesovortices

• Average Surge Genesis to Wind Damage Lead Time
  21 minutes
• Average Surge Genesis to Tornado Lead Time
• 18 minutes

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Tornado Warning Baseline

• Government Performance Requirements Act (GPRA)
  goals for 2013
• Probability of Detection (POD) 72
• False Alarm Rate (FAR) 70
• Tornado Warning Lead Time 13 minutes

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Three-Ingredients Method for Mesovortex Tornadoes

• Scenario If a Tornado Warning is issued as soon
  as all three ingredients are met

2013 GPRA Goals 2013 GPRA Goals 3 Ingredients Method Improvement
POD 72 90 22
FAR 70 65 5
Lead Time 13 minutes 18 minutes 5 minutes

• New Warning Decision Strategy vs. Current
• 18 minute lead time is a substantial increase
  over the average of 5 minutes currently offered
  by warning decision forecasters issuing Tornado
  Warnings upon the actual genesis of mesovortices

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Future Work

• SLS Manuscript and Poster
• Ernest F. Hollings Scholar Research
• Formal Research
• Conduct NOAA/NWS Training
• Interactive Webinars
• Work with Warning Decision Training Branch

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Summary

• Mesovortex genesis and strong intensification is
  favored
• In a portion of the QLCS in which the cold pool
  and ambient low-level shear are nearly balanced
  or slightly shear-dominant
  AND
• Where 0-3 km line-normal bulk shear magnitudes
  are equal to or greater than 30 knots AND
• Where a rear-inflow jet (RIJ) or enhanced outflow
  causes a surge or bow in the line.

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Summary (cont)

• 52 of 67 identified mesovorticies produced at
  least one report of winds 50 knots and/or a
  tornado
• Utilization of the three-ingredients method for
  issuing Tornado Warnings would greatly exceed
  2013 GPRA goals
• POD 90
• Lead Time 18 minutes

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Summary (cont)

• Results of utilizing the three-ingredients method
  offers a substantial and efficient means to
  reduce the loss of life, property, and disruption
  from high-impact events through the issuance of
  more accurate and timely warnings

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Acknowledgements

• Staff at Springfield WFO
• Chad Gravelle, Ph.D. for providing the 4-panel
  RUC files
• Ryan Kardell, Meteorological Intern, Springfield
  WFO for providing several programs used to
  collect and interrogate data

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Questions?
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