Quasi-Linear Convective System Tornado Warnings

Prospects for False Alarm Reduction

John P. Gagan and Jason S. SchaumannNational Weather Service

Springfield, MO

Background

• FY2008-09 tornado warnings issued at a substantial pace

• There were major events– January 2008 – 33 tornadoes– May 2009 – “Super Derecho”• 18 tornadoes• Wide swath of 70-90mph winds

• In all – 323 tornado warnings issued

• Why?– Rough transition to Storm Based Warnings?– “Hangover Effect” from larger severe events?– Unwarned events affecting decisions?

• Reality required a harsh look in the mirror:– Understanding of mesoscale – shaky– Understanding of QLCS radar features – shaky– Warning decisions – reactive, lacked process• Did we have a good pulse on what really mattered?

Background

• 133 Tornado Warnings FY2009– 84 QLCSs– 73% POD, 81% FAR

• QLCS tornadoes – significant challenge– Rapid “spin up”– Lead time - ~5 min

• Why not just stop issuing tornado warnings on QLCSs? Problem solved! Right?

How To Move Forward?

Buffalo, MO – 2/29/2012

Sunset Hills, MO – 12/31/2010

Sunset Hills, MO – 12/31/2010

• No waving the white flag – science to the rescue!• “Moneyball” approach– Physical understanding– Focus on variables that matter

• “Culture eats strategy for breakfast.”– Acknowledge the deficiencies, train…train…train.– “The approach in what you do results in what you get.”

Moneyball (2011)

A Plan, A Process

1. Three Ingredients Method for anticipating mesovortex genesis

2. Warning decision guidance

3. Polygon strategies for mesovortices

4. Radar interrogation strategies and time budget

Supports sound warning decisions by systematically honing in on areas where mesovortices and/or tornadoes are favored.

The Karate Kid (1984)

Warn Daniel-san!

QLCS Radar Interrogation StrategiesAn A-Z Process for Radar Operators

1. A portion of the QLCS in which the system cold pool and ambient low-level shear are nearly balanced or slightly shear-dominant

2. Where 0-3 km line-normal bulk shear magnitudes are equal to or greater than 30 knots

3. Where a rear-inflow jet (RIJ) or enhanced outflow causes a surge or bow in the line

Keep in mind that mesovortex genesis and strong intensification does not necessarily mean a tornado!

Three Ingredients MethodSchaumann and Przybylinski 2012

QLCS mesovortex genesis and strong intensification is favored where the following three criteria are co-located:

17 Nov 2013 Central Indiana

UDCZ

Slightly ShearDominant

Balanced

Slightly ColdPool Dominant

InflectionPoint

Shear/Cold Pool BalanceLocating Balanced/Slightly Shear Dominant Regions

1. Locate updraft/downdraft convergence zone (UDCZ) using 0.5° V/SRM products.2. Compare location of UDCZ to 0.5° reflectivity field.

0.5° SRM 0.5° Z

3 Apr 2015 Southern Missouri

UDCZ

0-3 km line-normal bulk shear magnitude ≥ 30 knots

Balanced or slightly shear dominant

RIJ or enhanced outflow causing surge or bow in the line

Favored Region forMesovortex Genesis

0-3 km Bulk Shear/MLCAPE

SPC Meso Page

0.5° SRM 0.5° Z

Three Ingredients MethodApplication

Statistical Performance of Three Ingredients Method2013 Hollings Study – Stanford et al.

• Correctly predicted 79% of mesovortices

• Falsely predicted a mesovortex 23% of the time

• Out of 67 mesovortices identified, the following two ingredients were always present:1. Line was balanced or slightly shear dominant (Ingredient #1)2. Local surge or bow in the line (Ingredient #3)

Hollings Study Case Domain

Cold SeasonWarm Season

Building on the Three IngredientsTornado Warning Guidance

• Radar signatures and mesoscale parameters which lead to increased tornado potential

• Combination of past research and local studies

• Further tilts odds in favor of radar operators

UDCZ

Warning Decision GuidanceScenarios for Considering a Tornado Warning

While one of the eight scenarios being met is often worthy of a Tornado Warning, confidence should further increase if more than one scenario and/or “nudgers” are present.

Enhanced Surge

Inflection Point

RIN

FIN

EF-1

0.5° SRM0.5° Z

Three Ingredients MethodologyBefore and After

FY09 to FY11

QLCS Warnings 107 63QLCS Tornado Events 47 49

Fully Warned 29 28Partially 4 4Unwarned 14 17

Verified 21 26Not Verified 86 37POD 68% 64%FAR 81% 59%

FY12 to FY15

FY09 to FY11

FY10 to FY12

FY11 to FY13

FY12 to FY14

FY13 to FY15

0

5

10

15

20

25

30

35

40

WFO Springfield QLCS Tornado Warnings and EventsThree Year Running Average

QLCS WarningsPower (QLCS Warnings)QLCS Tornado EventsLinear (QLCS Tornado Events)

Torn

ado

War

ning

and

Eve

nt C

ount

FY09 to FY11 compared to FY12 to FY15• QLCS tornado warnings reduced by 37%.• Unverified warnings reduced by 57%.• FAR drop of 22%• POD drop of 3.5%

May 2009 CaseWarning Execution Prior to the Three Ingredients Method

0-3 km Bulk Shear/VGP

SPC Meso Page

Success StoryRevisiting the Southern MO Line Segment

EF-1

0-3 km Bulk Shear/MLCAPE

SPC Meso Page

1. Schaumann, J. S., and R. W. Przybylinski, 2012: Operational Application of 0-3 km Bulk Shear Vectors in Assessing QLCS Mesovortex and Tornado Potential. Preprints, 26th Conf. on Severe Local Storms, Nashville, TN, AMS, P9.10.

2. 2013 Hollings Study by Stanford et al. (Available on WFO SGF website under Local Office Research)

3. SGF Google Site (SGF QLCS Guidelines)

4. Poster Sessions– Monday 3:00 to 4:30 PM – A Three Ingredients Approach to

Anticipating Mesovortex Genesis (Schaumann et al.)– Wednesday 2:30 to 4:00 PM – Application of the Three Ingredients

Method to QLCS Tornado Warning Decisions at NWS Bismarck (Mathews and Schaumann)John.Gagan@noaa.gov Jason.Schaumann@noaa.gov

References and Resources