Presentation on theme: "Quasi-Linear Convective System Tornado Warnings"— Presentation transcript:
1 Quasi-Linear Convective System Tornado Warnings Prospects for False Alarm ReductionJohn P. Gagan and Jason S. SchaumannNational Weather ServiceSpringfield, MO
2 Background FY2008-09 tornado warnings issued at a substantial pace There were major eventsJanuary 2008 – 33 tornadoesMay 2009 – “Super Derecho”18 tornadoesWide swath of 70-90mph windsIn all – 323 tornado warnings issuedGoing back to , WFO SGF issued warnings at a substantial clip. Certainly there were some substantial tornadic events:an incredibly rare January tornado outbreak in 2008 – 33 tornadoesAnd the “super derecho” of May 2009 – 18 tornadoes and a wide swath of 70-90mph straight-line windsHowever, a surprising number of tornado warnings were issued. 323 warnings to be exact.
3 Background Why? Reality required a harsh look in the mirror: 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 – shakyUnderstanding of QLCS radar features – shakyWarning decisions – reactive, lacked processDid we have a good pulse on what really mattered?Transition to storm based warnings, major events, unwarned events…these are few “convenient” explanations that could explain the large amount of warnings; but they gloss over the truth.Quote from “super derecho” event review - “This event again illustrated the challenge of issuing tornadoes in a squall line/QLCS environment from both a radar identification and polygon methodology standpoint.”The bottom line:The fundamental understanding of the mesoscale environment was shakyWarning decisions has become based more on reaction rather than process, focusing on what really matteredThe time had come to hit the “reset” button.
4 How To Move Forward? 133 Tornado Warnings FY2009 84 QLCSs73% POD, 81% FARQLCS tornadoes – significant challengeRapid “spin up”Lead time - ~5 minWhy not just stop issuing tornado warnings on QLCSs? Problem solved! Right?Focusing in on FY2009, almost 2/3rds of our tornado warnings were for QLCSs. While POD was respectable, FAR was 81%.Without a doubt, QLCSs are a major challenge.They are characterized by rapid spin ups and short lead times.Given the large amount of QLCS tornado warnings, one could logically conclude that the best way to minimize the number of warnings and reduce FAR would be to just simply stop issuing tornado warnings for QLCS events. PROBLEM SOLVED!!! Right????
8 A Plan, A Process No waving the white flag – science to the rescue! “Moneyball” approachPhysical understandingFocus 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.”We can do better than wave the “white flag.”Find a way to put the odds in the favor of the radar operator to make sound warning decisions. “Weatherball”Emphasis on physical processes, focusing on variables that matter.While an overwhelming amount of research has been conducted on the topic of environments and physical processes which lead to supercell tornadogenesis, research on environmental settings for QLCS tornadoes has been limited to mainly case studies.Moneyball (2011)
9 QLCS Radar Interrogation Strategies An A-Z Process for Radar Operators Three Ingredients Method for anticipating mesovortex genesisWarning decision guidancePolygon strategies for mesovorticesRadar interrogation strategies and time budgetThe Karate Kid (1984)Warn Daniel-san!What, when, where, how.Puts the odds in the favor of the radar operator to make sound warning decisions.Stats will shake outMain focus will be on three ingredients method, but we will briefly touch on tornado warning guidanceSupports sound warning decisions by systematically honing in on areas where mesovortices and/or tornadoes are favored.
10 Three Ingredients Method Schaumann and Przybylinski 2012 QLCS mesovortex genesis and strong intensification is favored where the following three criteria are co-located:A portion of the QLCS in which the system cold pool and ambient low-level shear are nearly balanced or slightly shear-dominantWhere 0-3 km line-normal bulk shear magnitudes are equal to or greater than 30 knotsWhere a rear-inflow jet (RIJ) or enhanced outflow causes a surge or bow in the line2012 Severe Local Storm conference (manuscript and poster)Mesovortex genesis and strong intensification does not necessarily mean a tornado!17 Nov 2013 Central IndianaKeep in mind that mesovortex genesis and strong intensification does not necessarily mean a tornado!
11 Shear/Cold Pool Balance Locating Balanced/Slightly Shear Dominant Regions 0.5° SRM0.5° ZSlightly ShearDominantUDCZInflectionPointBalancedDetermining ingredient #1Worst is not always first!Point out inflection pointMesovortices remain tethered to the UDCZSlightly ColdPool Dominant3 Apr Southern MissouriLocate updraft/downdraft convergence zone (UDCZ) using 0.5° V/SRM products.Compare location of UDCZ to 0.5° reflectivity field.
12 Three Ingredients Method Application 0-3 km Bulk Shear/MLCAPESPC Meso Page0.5° SRMUDCZ0.5° ZFavored Region forMesovortex Genesis0-3 km line-normal bulk shear magnitude ≥ 30 knotsBalanced or slightly shear dominantRIJ or enhanced outflow causing surge or bow in the line
13 Statistical Performance of Three Ingredients Method 2013 Hollings Study – Stanford et al. Correctly predicted 79% of mesovorticesFalsely predicted a mesovortex 23% of the timeOut of 67 mesovortices identified, the following two ingredients were always present:Line was balanced or slightly shear dominant (Ingredient #1)Local surge or bow in the line (Ingredient #3)67 mesovortices and 64 non-mesovortex surgesWithout ingredients 1 and 3, a mesovort is highly unlikely (probably don’t need a TOR)Cold SeasonWarm SeasonHollings Study Case Domain
14 Building on the Three Ingredients Tornado Warning Guidance Radar signatures and mesoscale parameters which lead to increased tornado potentialCombination of past research and local studiesFurther tilts odds in favor of radar operators
15 Warning Decision Guidance Scenarios for Considering a Tornado Warning UDCZEnhanced SurgeInflection PointRINFINEF-1Using the three ingredients method as a foundation, we have identified additional radar features and mesoscale parameters which indicate an increased likelihood for tornadoesEF-1 tornado near Vanzant, MODon’t want to wait until the last two scenarios if at all possiblePoster session this afternoon and again on Wednesday0.5° Z0.5° SRMWhile 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.
16 Three Ingredients Methodology Before and After FY09 to FY11FY12 to FY15QLCS Warnings QLCS Tornado Events Fully Warned Partially 4 4 Unwarned Verified Not Verified POD 68% 64% FAR 81% 59%Warnings reduced by 37% - almost identical number of tornado eventsUnverified warnings reduced by 57%FAR reduced 22%
17 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%Bottom line- the 3 ingredients methodology is having a positive affect on QLCS tornado warning accuracy.This remains a work in progress – the development of the scenarios and nudgers presented earlier will further refine the approach to QLCS tornado warnings.
18 May 2009 Case Warning Execution Prior to the Three Ingredients Method 0-3 km Bulk Shear/VGPSPC Meso PageLine – slightly outflow dominate, rearward leaning0-3km bulk shear was ~30kt, however the line normal component was poor – parallel to the lineApplying the 3 ingredients method to a line such as this today, would yielded 0 tornado warnings (11 were issued for this case alone).
19 Success Story Revisiting the Southern MO Line Segment 0-3 km Bulk Shear/MLCAPESPC Meso PageEF-1This example from southern MO is an example of a success story.Three ingredients method was met – along with multiple scenarios and nudgersEnd result:Quality warning decision, well executed polygon12 minute lead time for Vanzant (EF-1)13 minute lead for Pomona (EF-2)
20 References and Resources John.Gagan@noaa.gov Jason.Schaumann@noaa.gov 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, P9.10.2013 Hollings Study by Stanford et al. (Available on WFO SGF website under Local Office Research)SGF Google Site (SGF QLCS Guidelines)Poster SessionsMonday 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)
21 0-3 km Line-Normal Bulk Shear Threshold Ingredient #2 Mean 33.5Mean 25.9Lower Quartile30.2Shows statistical significance of 30 knot thresholdShear lower than 30 knots accounted for all of the “misses”P-value for line-normal 0-3 km bulk shear magnitudes was significantly lower than 1%.
22 Mesovortex Tornadoes Key Findings Average lead time between surge genesis and first tornado report was 18 minutesOrientation of vectors to UDCZ appears to play a key roleUsing a surge genesis as a possible precursor to draft a polygon can save valuable minutesSimilar magnitudes show that 0-3 km bulk shear vectors were nearly perpendicular to UDCZ for tornadic mesovorticesLower Quartile33.5Lower Quartile31.0
23 TeaserFY09 to FY11FY12 to FY15QLCS Warnings 107 Tornado Events 47 Fully Warned 29 Partially 4 Unwarned 14 Verified 21 Not Verified 86 POD 68% FAR 81%Teaser