severe weather: tornadoes and the enhanced fujita scale (james ladue)

Introducing the Introducing the Enhanced Fujita ScaleEnhanced Fujita Scale

Introducing the Introducing the Enhanced Fujita ScaleEnhanced Fujita Scale

Jim LaDue, Ed Mahoney, and Mark SessingJim LaDue, Ed Mahoney, and Mark Sessing

(NWS WDTB)(NWS WDTB)

National Press Foundation WorkshopNational Press Foundation Workshop

March 12th, 2007March 12th, 2007

ObjectivesObjectivesObjectivesObjectives

• Become aware of how tornadoes damage Become aware of how tornadoes damage structuresstructures

• Aware of What Goes Into an Enhanced Fujita Aware of What Goes Into an Enhanced Fujita Scale RatingScale Rating

• Walk through representative damage survey Walk through representative damage survey situationssituations

• Provide you links to comprehensive on-line Provide you links to comprehensive on-line Enhanced Fujita Scale trainingEnhanced Fujita Scale training

Wind effects on buildingsWind effects on buildingsWind effects on buildingsWind effects on buildings

Horizontal force

Bournoulli force

Internal pressurizationInternal pressurizationInternal pressurizationInternal pressurization

Failure of external envelope allows the wind to pressurize the interior

Internal pressurizationInternal pressurizationInternal pressurizationInternal pressurization

Collateral DamageCollateral DamageCollateral DamageCollateral Damage

Collateral damageCollateral damageCollateral damageCollateral damage

John Dean [mailto:John.Dean@powersouth.com]

Subvortices Subvortices Subvortices Subvortices

Adapted from Fujita, 1971

Did a suction vortex cause this damage?Did a suction vortex cause this damage?Did a suction vortex cause this damage?Did a suction vortex cause this damage?

Tornado damage is typically much longer Tornado damage is typically much longer than widethan wide

Tornado damage is typically much longer Tornado damage is typically much longer than widethan wide

Tornado converges debris toward the Tornado converges debris toward the center of a vortex or subvortexcenter of a vortex or subvortex

Tornado converges debris toward the Tornado converges debris toward the center of a vortex or subvortexcenter of a vortex or subvortex

Tornado converges debris toward the Tornado converges debris toward the center of a vortex or subvortexcenter of a vortex or subvortex

Tornado converges debris toward the Tornado converges debris toward the center of a vortex or subvortexcenter of a vortex or subvortex

The EF-ScaleThe EF-ScaleThe EF-ScaleThe EF-Scale

• Need more Need more damage damage indicatorsindicators

• recalibrate windsrecalibrate winds associated with F-scale associated with F-scale ratingsratings

• better better correlate wind correlate wind and ratingand rating

• account for account for construction construction variabilityvariability

• Flexibility, Extensibility, Flexibility, Extensibility, ExpandabilityExpandability

Evidence indicates a well Evidence indicates a well constructed house can be blown constructed house can be blown away by winds much less than away by winds much less than 260 mph 260 mph ((Phan and Simiu,2003)..

The framed house is one of only The framed house is one of only a few F-scale damage a few F-scale damage indicators.indicators.

EF-Scale Development has a wide range of EF-Scale Development has a wide range of participationparticipation

EF-Scale Development has a wide range of EF-Scale Development has a wide range of participationparticipation

• Led by Wind Science Led by Wind Science and Engineering and Engineering Center, Texas Tech Center, Texas Tech University, 7-8 March University, 7-8 March 20012001

• ObjectivesObjectives– Representative group of Representative group of

usersusers– ID key issuesID key issues– Make recommendationsMake recommendations– Develop a strategyDevelop a strategy

EF-Scale Damage Indicators (DIs)EF-Scale Damage Indicators (DIs)EF-Scale Damage Indicators (DIs)EF-Scale Damage Indicators (DIs)

• 28 DIs were identified by the Steering Committee28 DIs were identified by the Steering Committee• Each DI has several Degrees of Damage (DOD) Each DI has several Degrees of Damage (DOD) • DIs and DODs can be added or modifiedDIs and DODs can be added or modified

Framed house Single wide mobile home Small Retail Building

28 Damage Indicators (DI)28 Damage Indicators (DI)28 Damage Indicators (DI)28 Damage Indicators (DI)

Degrees of DamageDegrees of DamageDegrees of DamageDegrees of Damage

DOD for a Framed House, FR12

Meaning of the UB, EXP and LB WindsMeaning of the UB, EXP and LB WindsMeaning of the UB, EXP and LB WindsMeaning of the UB, EXP and LB Winds

EXP: Design exhibits typical

construction

UB: Design exceeds codes for typical US home,

better than average load path.

LB: Design fails to meet US building

codes, poor maintenance

and/or load path

One, Two Family House

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10

DOD

WIn

d S

peed (m

ph)

EXP

LB

UB

Win

d S

pee

d (

mp

h)

DOD to Wind Speed to EF-ScaleDOD to Wind Speed to EF-Scale

Wind speeds in mph, 3-second gust

Comparing F and EF-ScalesComparing F and EF-ScalesComparing F and EF-ScalesComparing F and EF-Scales

1 2 3 4 5 6 7 8 9 10 11 120Beaufort Scale

1 2 3 4 5 6 7 8 90 10 11 12Fujita Scale

0.6 1.0

Mach Scale

B1 B3B5

B7B9

B11

F0F1

F2

F3

F4

F5

F12M1.0

M0.6

M0.7

M0.8

B17

EF0EF1

EF2EF3

EF4

EF5

0 1 2 3 4 5

EF-Scale

The EF-Scale is a damage scale: speeds were estimated from the damage

Rating a DI with the EF-ScaleRating a DI with the EF-ScaleRating a DI with the EF-ScaleRating a DI with the EF-Scale

• Identify the DIIdentify the DI

• Match the damage Match the damage with the DODwith the DOD

• Modify the wind based Modify the wind based on construction qualityon construction quality

• Convert wind speed Convert wind speed estimate to ratingestimate to rating

FR12, DOD 7: Exterior Walls Collapsed, 132 mph, EF3

FR12, DOD 6: Large Section of roof removed, most walls standing, 122 mph, EF2

Step3: Integrating Constructions QualityStep3: Integrating Constructions QualityStep3: Integrating Constructions QualityStep3: Integrating Constructions Quality

Standard

Photographs ©Tim Marshall

ExceedingFailing

220 lbs 414 lbs(assuming no split wood)

1200 lbs

A strategy for surveying A strategy for surveying tornado tracks with the EF-Scaletornado tracks with the EF-Scale

A strategy for surveying A strategy for surveying tornado tracks with the EF-Scaletornado tracks with the EF-Scale

1.1. Identify DIs first with Identify DIs first with broad survey broad survey

2.2. Carefully identify Carefully identify DODs for each chosen DODs for each chosen DIDI

3.3. Rate the DIsRate the DIs4.4. Use the highest rated Use the highest rated

DIs to help rate the DIs to help rate the tornadotornado

LIRB: DOD 6: Inward, outward collapse of exterior walls. Expected wind = 137 mph EF3

FR12: DOD7: Exterior walls collapsed. Expected wind = 132 mph, EF2

http://meted.ucar.edu/resource/wcm/ftp/FinalNWSF-scaleAssessmentGuide.pdf

Rating a tornado event – exceeding your Rating a tornado event – exceeding your maximum rating possible?maximum rating possible?

Rating a tornado event – exceeding your Rating a tornado event – exceeding your maximum rating possible?maximum rating possible?

• A tornado can only be rated within the ranges of A tornado can only be rated within the ranges of available Damage Indicators (DIs)available Damage Indicators (DIs)

EF#^, where ^ means you’ve maximized the rating of a DI before EF5 was reached.

EF3^EF4^

Strengths of EF-ScaleStrengths of EF-ScaleStrengths of EF-ScaleStrengths of EF-Scale

• EF-ScaleEF-Scale– 28 DIs28 DIs

– Accounts for differences of Accounts for differences of structural integrity within a DIstructural integrity within a DI

– Wind speeds determined from Wind speeds determined from damagedamage

– Continuity from the F-scale Continuity from the F-scale

– Expandibility, Flexibility, Expandibility, Flexibility, ExtensibilityExtensibility

• F ScaleF Scale– Only a Couple DIsOnly a Couple DIs

– No accounting for differences of No accounting for differences of structural integrity within a DIstructural integrity within a DI

– Wind speeds not derived from Wind speeds not derived from damagedamage

Objectives: 5, EF-Scale strengths

EF-Scale limitationsEF-Scale limitationsEF-Scale limitationsEF-Scale limitations

• Change in scale may introduce artifacts into the Change in scale may introduce artifacts into the historical recordhistorical record

• Complicated Complicated • Wind speeds subject to change for each ratingWind speeds subject to change for each rating• No function relating wind speed to ratingNo function relating wind speed to rating• Debate continues about wind speed assignmentsDebate continues about wind speed assignments

Objectives: 6, EF-Scale limitations

Trial SurveyTrial SurveyTrial SurveyTrial Survey

1

Large Isolated Retail Building – DI 12 LIRB Large Isolated Retail Building – DI 12 LIRB Large Isolated Retail Building – DI 12 LIRB Large Isolated Retail Building – DI 12 LIRB

Large Isolated Retail Building – DI 12 LIRBLarge Isolated Retail Building – DI 12 LIRBLarge Isolated Retail Building – DI 12 LIRBLarge Isolated Retail Building – DI 12 LIRB

• DODsDODs• 11• 22• 33• 44• 55• 66• 77

Trial Survey: point 2Trial Survey: point 2Trial Survey: point 2Trial Survey: point 2

1

2

Metal Building System (MBS)Metal Building System (MBS)Metal Building System (MBS)Metal Building System (MBS)

Metal Building System (MBS)Metal Building System (MBS)Metal Building System (MBS)Metal Building System (MBS)

• DODsDODs• 11• 22• 33• 44• 55• 66• 77• 88• 99• 1010

Site 2

Trial SurveyTrial SurveyTrial SurveyTrial Survey

1

2

3

3A

Hardwood Tree, TH Hardwood Tree, TH Mobile Home Double Wide, MHDWMobile Home Double Wide, MHDW

Hardwood Tree, TH Hardwood Tree, TH Mobile Home Double Wide, MHDWMobile Home Double Wide, MHDW

3B

Hardwood Tree (TH)Hardwood Tree (TH)Hardwood Tree (TH)Hardwood Tree (TH)

• DODsDODs• 11• 22• 33• 44• 55

Site 3A

Mobile Home Double Wide, MHDWMobile Home Double Wide, MHDWMobile Home Double Wide, MHDWMobile Home Double Wide, MHDW

• DODsDODs• 11• 22• 33• 44• 55• 66• 77• 88• 99• 1010• 1111• 1212

Site 3B

Trial SurveyTrial SurveyTrial SurveyTrial Survey

1

23

4

House (FR12)House (FR12)House (FR12)House (FR12)

• DODsDODs• 11• 22• 33• 44• 55• 66• 77• 88• 99• 1010

Site 4

Trial Survey: Rate the whole tornadoTrial Survey: Rate the whole tornadoTrial Survey: Rate the whole tornadoTrial Survey: Rate the whole tornado

1

2

3

4

For More InformationFor More InformationFor More InformationFor More Information

http://www.wdtb.noaa.gov/courses/EF-scalehttp://www.wdtb.noaa.gov/courses/EF-scale