Overview of Damage Assessments Ron W. Przybylinski Science 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 assessments? Determine tornado intensity Estimate wind speeds Storm track, width Determine warning response

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.

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

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

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

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 mph EF Scale wind mph 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

28 Damage Indicators

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

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) 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

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 Wind Type Design Orientation of structure to the winds The upstream terrain Duration and gustiness of the wind Missiles

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.

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

Look 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?

Questions??