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Lesson 1: Introducing the Enhanced Fujita Scale. Dan McCarthy ( NWS SPC) and Jim LaDue (NWS WDTB). Goal and Scope of Training. The Goal of this Training is to effectively integrate the EF-Scale into the post storm damage assessment. Two lessons, each followed by a quiz

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Lesson 1: Introducing the Enhanced Fujita Scale


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    1. Lesson 1: Introducing the Enhanced Fujita Scale Dan McCarthy ( NWS SPC) and Jim LaDue (NWS WDTB)

    2. Goal and Scope of Training • The Goal of this Training is to effectively integrate the EF-Scale into the post storm damage assessment. • Two lessons, each followed by a quiz • Comparison of the EF and F-Scale • Using the EF-Scale to estimate tornado strength

    3. Motivation • EF-Scale to be used by the NWS starting 01 Feb, 2007 • More complex than F-Scale

    4. Lesson 1: Learning Objectives • Understand why the EF-Scale was created • Identify the methodology in creating the EF-Scale. • Understand the structure of the EF-Scale • Identify differences between the EF- and F-Scale • Understand the strengths of the EF-Scale • Understand the limitations of the EF-Scale

    5. Performance Objective • Apply the strengths and limitations of the EF-Scale when rating damage produced by a tornado

    6. Why the EF-Scale was created • Need more damage indicators • recalibrate winds associated with F-scale ratings • better correlate wind and rating • account for construction variability • Flexibility, Extensibility, Expandability The framed house is one of only a few F-scale damage indicators. Evidence indicates a well constructed house can be blown away by winds much less than 260 mph (Phan and Simiu,2003). Objectives: 1, Why the EF-Scale?

    7. EF-Scale history: Steering Committee Organize a Steering Committee (2001) Michael Riley - NIST Brian Smith, NWS OAX Joe Schaefer - SPC Jim McDonald - TTU Don Burgess – NSSL Kishor Mehta -TTU Objectives: 2, Methodology

    8. The Steering Committee Organizes a Forum • Led by Wind Science and Engineering Center, Texas Tech University, 7-8 March 2001 • Objectives • Representative group of users • ID key issues • Make recommendations • Develop a strategy Objectives: 2, Methodology

    9. The forum identifies EF-Scale development strategies • Identify additional Damage Indicators (DI)s • Correlate damage to wind speed • Degrees of Damage (DOD) for each DI • Preserve the historical database • Seek input from users • Maximize usability Objectives: 2, Methodology

    10. EF-Scale Damage Indicators (DIs) • 28 DIs were identified by the Steering Committee • DIs and DODs can be added or modified • Each DI has several Degrees of Damage (DOD) Framed house Single wide mobile home Small Retail Building Objectives: 2, methodology; 3, EF-Scale structure

    11. 28 Damage Indicators Residences Commercial/retail structures Schools Professional buildings Metal buildings/canopies Towers/poles Vegetation Objectives: 3, EF-Scale structure

    12. Degrees of Damage DOD for a Framed House, FR12 or DOD2 Objectives: 2, methodology; 3, EF-Scale structure

    13. Wind Speed (mph) Reason behind an upper and lower bound wind speed EXP: Design exhibits typical construction Objectives: 2, methodology; 3, EF-Scale structure

    14. Wind Speed (mph) Reason behind an upper and lower bound wind speed (contd) UB: Design exceeds codes for typical US home, better than average load path. EXP: Design exhibits typical construction LB: Design fails to meet US building codes, poor maintenance and/or load path Objectives: 2, methodology; 3, EF-Scale structure

    15. How the winds were derived for each DOD • Possible Candidates • Structural analysis to determine resistance and theoretical failure modes • Simulation of tornado winds to produce structural damage • Expert Elicitation • Chosen method? • Expert Elicitation Chosen Experts: Greg Forbes – Meteorologist, TWC Don Burgess – Meteorologist, NSSL Doug Smith – Engineer, TTU Tim Reinhold – Engineer, Clemson University Tom Smith – Architect, Consultant Tim Marshall – Meteorologist/Engineer, Haag Engineers Objectives: 2, EF-Scale methodology

    16. Derive Wind Speeds by Expert Elicitation Describe the DIs and DODs and present to experts Experts individually estimate wind speeds for each DOD Train the experts in elicitation process Mehta and McDonald analyze results and present to experts for review Iterate again Present final estimates to forum for review Experts revise their wind speeds Objectives: 2, EF-Scale methodology

    17. Degrees of Damage Note some consecutive DODs have larger overlap than others Example DODs for a Framed House DI (FR12 or DI2) Objectives: 3, EF-Scale structure

    18. Wind Speed (mph) Degrees of Damage Note some consecutive DODs have larger overlap than others Example DODs for a Framed House DI (FR12 or DI2) Objectives: 2, methodology; 3, EF-Scale structure

    19. Y = 0.6246x + 36.393 R2 = 0.9118 Relating the F-scale with the EF-Scale • Need of historical continuity • 2nd set of experts assigned F-scale ratings to the same damage descriptions • Median F-scale wind speeds compared to that of expected EF-Scale wind speeds Bill Bunting – NWSFO – Fort Worth, Texas Brian Peters – NWSFO – Calera, Alabama John Ogren – NWSFO – Indianapolis, Indiana Dennis Hull – NWSFO – Pendleton, Oregon Tom Matheson – NWSFO – Wilmington, North Carolina Brian Smith – NWSFO – Valley, Nebraska F5 to EF5 threshold wind speed The F-Scale wind speed was converted from the fastest ¼ mi to a 3 sec gust. Objectives: 2, methodology; 4, EF vs F-Scale

    20. F-Scale Converted to EF-Scale Wind speeds in mph, 3-second gust Objectives: 3, EF-Scale structure; 4, EF vs F-Scale

    21. DOD to Wind Speed to EF-Scale Wind speeds in mph, 3-second gust Objectives: 3, EF-Scale structure

    22. Comparing Beaufort, F, and Mach Scales These scales have wind speed defined first, impacts/damage were assigned to wind speeds. M1.0 F12 M0.8 Beaufort: V = 1.870B3/2mph F – scale: V = 14.1(F+2)3/2mph Mach scale: V = (742 +1.3)Mmph M0.7 M0.6 F5 B17 F4 F3 B11 B9 F2 B7 F0 B5 F1 B3 B1 0 1 2 3 4 5 6 7 8 9 10 11 12 Fujita Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 0.6 1.0 Mach Scale Beaufort Scale Objectives: 3, EF-Scale structure; 4, EF vs F-Scale

    23. 4 5 0 1 2 3 Comparing F and EF-Scales The EF-Scale is a damage scale: speeds were estimated from the damage M1.0 F12 M0.8 M0.7 M0.6 EF-Scale EF5 F5 EF4 B17 EF3 F4 EF2 EF1 F3 B11 EF0 B9 F2 B7 B5 F1 B3 F0 B1 0 1 2 3 4 5 6 7 8 9 10 11 12 Fujita Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 0.6 1.0 Mach Scale Beaufort Scale Objectives: 3, EF-Scale structure; 4, EF vs F-Scale

    24. DOD to Wind Speed to EF-Scale question Quiz: What DOD best corresponds with this damage? Objectives: 3, EF-Scale structure

    25. EF-Scale_L1_1

    26. DOD to Wind Speed to EF-Scale review Expected wind 97 mph Objectives: 3, EF-Scale structure

    27. EF-Scale answer Wind Speed in mph, 3-Second gust Objectives: 3, EF-Scale structure

    28. EF-Scale 28 DIs Accounts for differences of structural integrity within a DI Wind speeds determined from damage Continuity from the F-scale Expandibility, Flexibility, Extensibility F Scale Only a Couple DIs No accounting for differences of structural integrity within a DI Wind speeds not derived from damage Strengths of EF-Scale Objectives: 5, EF-Scale strengths

    29. EF-Scale limitations • Change in scale may introduce artifacts into the historical record • Complicated • Wind speeds subject to change for each rating • No function relating wind speed to rating • Debate continues about wind speed assignments Objectives: 6, EF-Scale limitations

    30. EF-scale_L1-2

    31. Summary: Lesson 1 • EF-Scale created to provide more DIs, more realistic wind speeds • EF-Scale winds were estimated using expert elicitation • EF-Scale contains 28 DIs, each with several DODs ranging from first damage to destruction or if the estimated wind speeds correspond to an EF 5 rating. • EF-Scale winds significantly lower than F-scale for EF (F3) and higher • EF-Scale is complicated requiring a longer time for familiarization Objectives: 1-6

    32. References and suggested reading McDonald, J.R. and K.C. Mehta, 2001: Summary report of the Fujita Scale forum. Wind Science and Engineering, Texas Tech University, Lubbock, TX, 36 pp. Phan, L.T. and E. Simiu, 1998: The Fujita tornado intensity scale: a critique based on observations of the Jarrell tornado of May 27, 1997. NIST Tech. Note 1426, U.S. Department of Commerce, Gaithersburg, MD, 20 pp. SSHAC, 1997: Recommendations for probabilistic seismic hazard analysis: guidelines on uncertainty and use of experts, NUREG/CR6372, UCRL-ID-122160, Vol. I, Lawrence Livermore National Laboratory, Livermore, CA, 131 pp. Suggested reading: A Recommendation for the Enhanced Fujita Scale: http://www.spc.noaa.gov/efscale/

    33. In Lesson 2 • Lesson 2 provides you a chance to use the EF-Scale on some damage tracks

    34. Contacts • If you have any questions about this lesson, contact • Jim LaDue, James.G.LaDue@noaa.gov • Dan McCarthy, Daniel.McCarthy@noaa.gov