Overview of Damage Assessments Ron W. Przybylinski Science and Operations Officer NWS St. Louis.

Overview of Damage Assessments

Ron W. PrzybylinskiScience and Operations Officer

NWS St. Louis

Outline

Damage Patterns (Tornadic and Downburst (Microbursts)

Brief review of the Enhanced Fujita (EF) Scale

Example – “You Make the Call” What can I do for you. What

can you do for me.

Why do damage Why do damage assessments?assessments? Determine tornado

intensity

Estimate wind speeds

Storm track, width

Determine warning response

Heard this Before?Heard this Before?

It sounded like a freight train The trees (or whatever) are twisted Only a tornado could do this much

damage I felt my ears “pop”

Tornadic Damage

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

From Dr. Ted Fujita – Univ. of Chicago

June 10 2003 – tornadic damage two miles NNW of Nashville IL – weak tornado.

BAMEX Project 2003

House trailer damage from a violent tornado –2:00 am CST

November 6 2007 Evansville IN.

Eastbrook Mobile Home Park – southeast of Evansville Indiana

View from a plane viewing SE - Eastbrook Mobile Home Park

Multiple Vortex Tornado

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

Remains of a corn field from a violent tornado

Are you able to observe part of a convergent pattern ?

Downburst clusters associated with bow echoes

Classic example of a microburst – starburst pattern

Small part of a downburst cluster over southern Clinton County Illinois – July 21 2006

Characteristic Tornado Downburst

Aspect RatioAspect Ratio Long & thin Short & wide

Damage gradientDamage gradient High Low

Trajectories of Trajectories of debrisdebris

Narrow and convergent

Broad and divergent

Appearance of Appearance of damagedamage

Chopped up, chaotic

Laid out neatly

Visual clues from Visual clues from groundground

Swirls, mud splattered on walls

No swirls, no mud

Visual clues from Visual clues from aircraftaircraft

Vortex mark Starburst pattern

Damage characteristics we look for:

Introduction to the Enhanced Fujita (EF) scale

Dr. Ted Fujita (1971) developed the Fujita scale to provide a method to rate the intensity of tornadoes.

However after 33 years of using the Fujita scale, users have found many limitations to this scale (e.g. lack of damage indicators).

In many cases NWS personnel would over estimate the wind speeds with tornadoes.

Enhanced Fujita (EF) scale

Steering committee (23 members) developed the following:

Identify “Damage Indicators.” Correlate appearance of damage

to wind speed Preserved the historical data base Seek additional input from users

EF Scale vs. Traditional Fujita Scale Wind Speed Ranges

Fujita Scale wind Fujita Scale wind mphmph EF Scale wind mphEF Scale wind mph

3-Second Gust3-Second Gust 3-Second Gust3-Second Gust

F0F0 45 - 7845 - 78 EF0EF0 ≤ ≤ 8585

F1F1 79 - 11779 - 117 EF1EF1 86 – 11086 – 110

F2F2 118 - 161118 - 161 EF2EF2 110 – 135110 – 135

F3F3 162 - 209162 - 209 EF3EF3 136 – 165136 – 165

F4F4 210 - 261210 - 261 EF4EF4 166 – 200166 – 200

F5F5 262 - 317262 - 317 EF5EF5 ≥ ≥ 200200

28 Damage Indicators

EF Scale Development

Each DI has several Degrees of Damage (DOD) Range from no damage to total

destruction Arranged in order of increasing damage

One-and Two-Family Residences (FR12)

Typical Construction: Asphalt shingles, tile, slate or metal roof

covering Flat, gable, hip, mansard or mono-sloped roof or

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

rafter construction Brick veneer, wood panels, stucco, EIFS, vinyl or

metal siding Wood or metal stud walls, concrete blocks or

insulating concrete panels Attached single or double garage

One-and Two-Family Residences (FR12)

One-and Two-Family Residences Degree

of Damage (DODs)

DOD Damage DescriptionExp

(mph)

LB (mph

)

UB (mph

)

1 Threshold of visible damage 65 53 80

2 Loss of roof covering material (<20%), gutters and/or awning; 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 covering material (>20%); collapse of chimney; garage doors collapse 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 walls remain 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

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)

One-and Two-Family Residences

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

One-and Two-Family Residences

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

Recommended steps for assessing tornado damage

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

buildings, power poles, etc…) that tend to indicate the highest wind in the damage path

Assign an EF-scale to individual DIs – document Rate the tornado intensity by applying the

highest rated 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

Structures’ Response to Structures’ Response to WindWind

Type Design Orientation of structure to the

winds The upstream terrain Duration and gustiness of the wind Missiles

Pressure on the building’s interior increases, resulting in additional outward forces. That is why opening windows is not a good idea.

Failure Points

Rafter/top plate Roof joist/top

plate

Wall stud/bottom plate

Wall/foundation

Look For ReinforcementsLook For Reinforcements

You make the call

Large Industrial building

Another Image

Remains of a corn field

What can I do to help you out?

What can you do to help me out?