Andy Bailey National Weather Service Forecast Office Pleasant Hill / Kansas City

Transcription

1 Andy Bailey National Weather Service Forecast Office Pleasant Hill / Kansas City

2 Agenda Why we do surveys Tools we use to conduct surveys What the damage can tell us about the storm Anatomy of a Survey Wind damage processes EF Scale and EF Kit How to give us a headstart

3 Why do we bother to do surveys? Evaluate our performance Learn from events-improve our understanding of the atmosphere Maintain a climatological database Satisfy media/public hunger for a label (or someone to blame May 1&2)

4 The Tools We Use Damage Survey go Kit

5 Computer The Tools We Use EF Kit software GPS mapping (if no iphone) Pretty clunky

6 The Tools We Use Camera/Video Cam Document Damage visually (again if no iphone) Capture eye-witness accounts Gadget management fatigue

7 Binoculars The Tools We Use Helpful to see what is stuck in fence line ¼ mile away Saves time

8 Maps The Tools We Use Detailed road networks Draw crude damage path directly on Work with no power!

9 Clipboard Paper Pens Take notes Explain pictures Justification of ratings Capture eye witness accounts, times, etc. Can t accidentally delete

10 The Tools We Use iphone Communications Voice/ twitter/ facebook/ sms/ GPS and compass Camera and Video Cam Internet access and mapping Miracle tool

11 The Tools We Use iphone MotionX GPS app Allows photos to be geotagged with notes added, then shared via , twitter, and fb $2.99

12 The Tools We Use Example MotionX GPS output

13 What the Survey Can Tell About Storm How strong were winds Vs.

14 What the Survey Can Tell About Storm Tornadic vs. Straight-line Winds

15 Tornado vs. Downburst Differentiating between the two. MYTH: Twisted trees or signs, or trees laying in different directions must mean tornado damage. FACT: No tree is perfectly symmetrical and will fall differently depending on wind direction, weight of canopy, and integrity. FACT: Signs may also twist because of unequal footings or posts. Could also blow around after initial break and appear twisted Tornado winds are essentially straight line to any one particular object. Tornado would have to have similar diameter to bring winds from several directions.

16 Tornado vs. Downburst Differentiating between the two. MYTH: Witness reported a roaring sound with passage of storm must be a tornado. FACT: Strong wind produces the roaring sound, and can occur with either tornadoes or straightline wind storms. MYTH: My house was damaged. It must have been a tornado. FACT: Straight line winds can produce EF0 to EF2 tornado damage.

17 What the Survey Can Tell About Storm What would damage path look like for a tornado?

18 What the Survey Can Tell About Storm What would damage path look like for a tornado? Damage path is convergent, relatively narrow and strongest on right side of the damage path

19 Tornado vs. Downburst Tornado damage is convergent. Most tornado damage on right flank.

20 Best way to differentiate is an aerial survey Tornado damage is convergent. Tornado vs. Downburst

21 What the Survey Can Tell About Storm What would damage path look like for straight-line winds?

22 What the Survey Can Tell About Storm What would damage path look like for straight-line winds? Damage path is divergent, wider, and strongest on along the damage path

23 Tornado vs. Downburst Downbursts exhibit straight or divergent damage patterns, and are often fairly widespread.

24 What the Survey Can Tell About Storm Was the warning received and understood? Timing of events Readiness of community

25 Anatomy of a Damage Survey

26 Anatomy of a Damage Survey NWS Gets word of damage Usually we understand the potential Use radar and reports to identify target locations, at least as a start Contact local EMD Drive to site

27 Anatomy of a Damage Survey Upon arrival, we attempt to get a local EMD or law enforcement escort Try to get a feel for the damage path and nature (aerial support helps) Begin methodically, but quickly moving from site to site, documenting damage We note: Location, photos, degree of damage, direction of debris

28 Anatomy of a Damage Survey Note quality/consistency of DIs Begin to send data back to office Gather eye-witness accounts Affix a rating Coordinate with the NWS office Coordinate with local officials Conduct media interviews

29 Damage Surveys on the Web

30 Google Earth Output

31 Wind damage processes Buildings are designed so gravity holds them in place Forces from extreme wind act against the designed gravity-based load path This misunderstanding bred the open window myth.

32 Wind damage processes Recall the Bernoulli effect Air has to flow faster above the object, with lower pressure causing lift. This same process works on walls and roofs of houses.

33 Wind damage processes Weak point failures such as windows and garages compound the problem. This internal pressure aides the outside lift. FEMA 342

34 Wind damage processes Garage doors are common weak points, and are often the first failure point. This can result in downstream projectile damage to structures which otherwise may not have occurred (Important F-scale considerations)

35 F-scale: History and Definition Developed in 1971 by University of Chicago professor Dr. T. Theodore Fujita Wind vs Damage Table, mainly correlated to wood frame houses (wind at standard anemometer height of 10 meters) Rating actually done by assessing damage. Wind speeds inferred by damage. Drawbacks Difficult to estimate in open areas or with lack of standard structures Wind speeds appear to be too strong in higher end of scale Too few # of damage indicators

36 EF Scale An improvement over the old Fujita scale 28 separate damage indicators Based on damage assignment on more than one structure (if available) Needed for consistent tornado ratings

37 EF Scale Difficulties Identical tornadoes moving at different speeds produce different damage Tornado size cannot be used to rate damage Tornado hits nothing in open area Gaps in damage path Likely caused by weakening of near surface wind due to friction from structures and trees producing tree top level damage. Video does not support skipping or quick withdraw back into clouds.

38 EF Scale Identification of appropriate damage indicators is first step Structural integrity or integrity of tree should be considered however. Shoddy construction or weak connections between foundation, walls, and roof can reduce the EF-scale rating by 1 or more Orientation of weak points such as garage doors relative to wind can reduce F-scale rating (failure caused indirectly by weak point)

39 Residences Commercial/retail structures Schools Professional buildings Metal buildings/canopies Towers/poles Vegetation

40 DOD Damage Description EXP LB UB 1 Threshold of visible damage 2 Loss of roof covering material (<20%), gutters and/or awning; loss of vinyl or metal siding 3 Broken glass in doors and windows 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 5 Entire house shifts off foundation 6 Large sections of roof structure removed; most walls remain standing 7 exterior walls collapsed 8 Most walls collapsed except small interior rooms. 9 All walls collapsed DOD for a Framed House, DI2 10 Destruction of engineered and/or well constructed residence; slab swept clean

41 An easy to use computer program Allows for easy application and use of EF Scale PC based, even from thumb drive

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46 Provide street addresses and lat/lon coordinates of worst of damage Describe nature of damage Estimate damage path width Provide photos (not just close ups)

47 Conclusion A good quality damage survey requires: a knowledge of meteorology / radar interpretation basic construction knowledge Ability to work quickly, yet thoroughly Organization Sensitivity