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Overview of Damage Assessments

Ron W. PrzybylinskiScience and Operations Officer

NWS St. Louis

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OutlineDamage Patterns (Tornadic andDownburst (Microbursts)Brief review of the EnhancedFujita (EF) ScaleExample – “You Make the Call” What can I do for you. What

can you do for me.

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Why do damage assessments?Determine tornadointensity

Estimate wind speeds

Storm track, width

Determine warningresponse

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Heard this Before?

It sounded like a freight trainThe trees (or whatever) are twistedOnly a tornado could do this muchdamageI felt my ears “pop”

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Tornadic Damage

Convergence pattern – arrows pointing to thecenter axis of the tornadic damage path (Red) .

From Dr. Ted Fujita – Univ. of Chicago

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House trailer damage from a violenttornado – 2:00 am CST

November 6 2007 Evansville IN .

Eastbrook Mobile Home Park – southeast of Evansville Indiana

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View from a plane viewing SE -

Eastbrook Mobile Home Park

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Multiple Vortex Tornado

Multiple Vortex pattern – the strongest winds often occurwith this type of ground pattern (suction vortices) .

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Remains of a corn field from

a violent tornado

Are you able to observe part of a convergent pattern ?

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Downburst clusters

associated with bow echoes

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Small part of a downburst clusterover southern Clinton County

Illinois – July 21 2006

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Characteristic Tornado Downburst

Aspect Ratio Long & thin Short & wide

Damage gradient High Low

Trajectories of debris

Narrow andconvergent

Broad and divergent

Appearance of

damage

Chopped up, chaotic Laid out neatly

Visual clues fromground

Swirls, mudsplattered on walls

No swirls, no mud

Visual clues fromaircraft

Vortex mark Starburst pattern

Damage characteristics we

look for:

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Introduction to theEnhanced Fujita (EF) scale

Dr. Ted Fujita (1971) developed the Fujitascale to provide a method to rate the

intensity of tornadoes.However after 33 years of using the Fujitascale, users have found many limitations tothis scale (e.g. lack of damage indicators ).In many cases NWS personnel would overestimate the wind speeds with tornadoes.

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Enhanced Fujita (EF) scale

Steering committee (23 members)developed the following:Identify “Damage Indicators.” Correlate appearance of damage towind speedPreserved the historical data baseSeek additional input from users

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EF Scale vs. Traditional FujitaScale Wind Speed Ranges

Fujita Scale wind mph EF Scale wind mph

3-Second Gust 3-Second Gust

F0 45 - 78 EF0 ≤ 85

F1 79 - 117 EF1 86 – 110

F2 118 - 161 EF2 110 – 135

F3 162 - 209 EF3 136 – 165

F4 210 - 261 EF4 166 – 200

F5 262 - 317 EF5 ≥ 200

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28 Damage Indicators

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One-and Two-FamilyResidences (FR12)

Typical Construction: Asphalt shingles, tile, slate or metal roof coveringFlat, gable, hip, mansard or mono-sloped roof or

combination thereof Plywood/OSB or wood plank roof deck Prefabricated wood trusses or wood joists and rafterconstruction

Brick veneer, wood panels, stucco, EIFS, vinyl or metalsidingWood or metal stud walls, concrete blocks or insulatingconcrete panels

Attached single or double garage

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One-and Two-FamilyResidences (FR12)

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One-and Two-Family ResidencesDegree of Damage (DODs)

DOD Damage Description Exp(mph)

LB(mph)

UB(mph)

1 Threshold of visible damage 65 53 80

2 Loss of roof covering material (<20%), gutters and/orawning; loss of vinyl or metal siding 79 63 97

3 Broken glass in doors and windows 96 79 114

4 Uplift of roof deck and loss of significant roof coveringmaterial (>20%); collapse of chimney; garage doorscollapse inward or outward; failure of porch or carport 97 81 116

5 Entire house shifts off foundation 121 103 141

6 Large sections of roof structure removed; most wallsremain standing 122 104 142

7 Exterior walls collapsed 132 113 153

8 Most walls collapsed, except small interior rooms 152 128 173

9 All walls collapsed 170 142 198

10 Total destruction of entire building, slab swept clean 200 165 220

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One-and Two-Family Residences

FR12: DOD4: Uplift of roof deck and loss of roof covering (>20%);garage door collapses outward (LB 81 mph; UB 116 mph; Exp 97 mph)

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One-and Two-Family Residences

FR12: DOD7: Top floor (First floor in this case) exterior wallscollapsed. (LB 113 mph; UB 150 mph; Exp 132 mph).

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One-and Two-Family Residences

FR12: DOD10: Total destruction of entire building(LB 165 mph; UB 220 mph; Exp 200 mph).

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Recommended steps forassessing tornado damage

Conduct a survey (aerial if possible)Select several damage indicators (trees, buildings,

power poles, etc…) that tend to indicate the highestwind in the damage path Assign an EF-scale to individual DIs – documentRate the tornado intensity by applying the highestrated DI, provided there is supporting evidence of similar damage nearby.Document the basis for assigning the EF-Scale, and

record other pertinent data related to the event

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Structures’ Response to Wind

Type

DesignOrientation of structure to the windsThe upstream terrain

Duration and gustiness of the windMissiles

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Pressure on the building’s interior increases, resulting inadditional outward forces. That is why opening windows isnot a good idea.

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Failure Points

Rafter/top plateRoof joist/top

plate

Wall stud/bottomplateWall/foundation

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You make the call

Large Industrial building

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Another Image

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Remains of a corn field

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What can I do to help you out?

What can you do to help me out?

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