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

2. 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.

3. Why do damage assessments?
Determine tornado intensity
Estimate wind speeds
Storm track, width
Determine warning response

4. 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”
These are all myths. All these things can happen with downburst or straight-line winds.

5. Tornadic Damage
From Dr. Ted Fujita – Univ. of Chicago
Convergence pattern – arrows pointing to the center axis of the tornadic damage path (Red).

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

7. House trailer damage from a violent tornado –2:00 am CST November 6 2007 Evansville IN.
Eastbrook Mobile Home Park – southeast of Evansville Indiana

8. View from a plane viewing SE - Eastbrook Mobile Home Park

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

10. Remains of a corn field from a violent tornado
Are you able to observe part of a convergent pattern ?

12. Downburst clusters associated with bow echoes

13. Classic example of a microburst – starburst pattern

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

15. Damage characteristics we look for:
Tornado
Downburst
Aspect Ratio
Long & thin
Short & wide
Damage gradient
High
Low
Trajectories of debris
Narrow and convergent
Broad and divergent
Appearance of damage
Chopped up, chaotic
Laid out neatly
Visual clues from ground
Swirls, mud splattered on walls
No swirls, no mud
Visual clues from aircraft
Vortex mark
Starburst pattern

16. 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.

17. 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

18. EF Scale vs. Traditional Fujita Scale Wind Speed Ranges
Fujita Scale wind mph
EF Scale wind mph
3-Second Gust F0
EF0
≤ 85 F1
EF1
86 – 110 F2
EF2
110 – 135 F3
EF3
136 – 165 F4
EF4
166 – 200 F5
EF5
≥ 200

19. 28 Damage Indicators

20. Each DI has several Degrees of Damage (DOD)
EF Scale Development
Each DI has several Degrees of Damage (DOD)
Range from no damage to total destruction
Arranged in order of increasing damage

21. 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

22. One-and Two-Family Residences (FR12)

23. One-and Two-Family Residences Degree of Damage (DODs)
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/or awning; loss of vinyl or metal siding 79 63 97 3
Broken glass in doors and windows 96
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 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
198 10
Total destruction of entire building, slab swept clean
200
165
220

24. 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)

25. 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).

26. One-and Two-Family Residences
FR12: DOD10: Total destruction of entire building (LB 165 mph; UB 220 mph; Exp 200 mph).

27. 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

28. Structures’ Response to Wind
Type
Design
Orientation of structure to the winds
The upstream terrain
Duration and gustiness of the wind
Missiles

29. Openings result in interior pressurization.
Buildings don’t explode- actually, they opposite occurs- they implode. Greatest outward wind pressures occur around windward walls, roof corners, eaves, and ridges.
Structures are not only affected by the strength of the wind, but by its duration, gustiness, and by the direction from which the wind approaches the structure. Also, damage can depend on what objects were used as missiles.
Pressure on the building’s interior increases, resulting in additional outward forces. That is why opening windows is
not a good idea.

30. Failure Points Rafter/top plate Roof joist/top plate
Wall stud/bottom plate
Wall/foundation

31. Look For Reinforcements

32. You make the call
Large Industrial building

33. Another Image

34. Remains of a corn field

35. What can I do to help you out?
What can you do to help me out?

36. Questions??