Executive Summary
Just two weeks after a tornado caused extensive damage to Moore, OK, on 31 May 2013, El Reno, OK, was hit by
another powerful tornado. El Reno is a little less than 30 miles to the north-west of Moore, and it has a population
of 17,510 in 6,752 homes. The tornado tracked through mainly rural areas south of the town itself (south of
Interstate 40). The unsettled weather spawned multiple vortices and several (nine) tornadoes in El Reno, Yukon,
Mustang, near Moore, Del City, Watova and Oklahoma City. The most deadly was the El Reno. NWS reports a
16.2-mile curvilinear path of the tornado, and a maximum damage swath of 2.6 miles, making it the widest
tornado on record. Building damage was relatively limited due to the rural track taken by this tornado. There were
20 confirmed fatalities, including the three storm chasers, Tim Samaras, his son, Paul and a videographer with his
team. This was indeed a tragic loss to forecasting community.
This report was prepared from online sources by University of Florida civil engineering students in Prof. David O.
Prevatt’s Research Group. It is part of their learning in forensic engineering and post-disaster damage
investigation. Students were tasked to gather information from online sources and collate information on the
tornado (from the National Weather Service, storm chaser Twitter feeds), injuries and fatalities (from media
reports) and on structures (from the US Census Bureau and building code websites).
Researchers at the University of Florida and elsewhere will continue to document tornado outbreaks as they occur,
and in parallel our research to understand and quantify the strength of tornado loads and their interaction with
vulnerable wood-framed structures is continuing. It is our thesis, that engineering solutions can be found to
improve the tornado-resistance of houses. These solutions come at a price, yet to be determined, once scientists
have a better idea of the loads, and society determines what risks are acceptable. Stronger buildings can be built
quite economically today that would mitigate structural damage and provide better life safety protection – it is up
to communities and their leaders to decide whether they wish to pursue such resilient and sustainable approaches
or whether to continue with the status quo.
Please visit our website, for further information http://windhazard.davidoprevatt.com. Background information
and our previous damage survey blogs can be found on Dr. Prevatt’s webpage, www.davidoprevatt.com, including
the Tuscaloosa Tornado Damage Survey Report. A list of helpful references is included at the end of this report.
Your questions and comments on any aspects of our work are most welcome. Please direct your enquiries to NSF
Graduate Research Fellow, and PhD Graduate Student, Mr. David B. Roueche, who can be reached at
<PRESIDIO_ANONYMIZED_EMAIL_ADDRESS>.
About the Wind Hazard Damage Assessment Team
The Wind Hazard Damage Assessment Team was created through support from the NSF Award #1150975. Its
mission is to train university students interested in building construction, engineering and architecture in the
forensic engineering and techniques for post-hazard damage surveys and data collection. The team has surveyed
damage after several Florida tornadoes and continuously monitors the prevalence of tornadoes worldwide.
Ultimately the Team hopes to inspire upcoming engineers and building professionals in hopes to change the
paradigm of widespread catastrophic damage to houses in tornadoes. Mr. Jeandona (JD) Doreste, is a civil
engineering undergraduate student at UF and Webmaster of the Wind Hazard Damage Assessment Team site. JD
is actively recruiting other UF students to join the team, and he can be reached at <PRESIDIO_ANONYMIZED_EMAIL_ADDRESS>. 
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
2
PREDICTION OF WEATHER
Initial expectations for tornado risk on May 31st were very significant (Figure 1), with the Storm
Prediction Center tornado outlook showing a 15% probability of tornado genesis in Central Oklahoma,
Southern Kansas, and Southern Missouri.
TWEETS
Storm chasers were on high alert, expecting significant tornado outbreaks for Central Oklahoma,
Southwest Missouri, and Southeast Kansas.
Figure 1: Tornado Probability for May 31, 2013 as Issued by NWS SPC at 17:00 PM UTC on Same Day
(Source: http://www.spc.noaa.gov/products/outlook/archive/2013/day1otlk_20130531_1630.html )
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
3
TIMING OF TORNADO
The timeline of the tornado as it formed and impacted the city of El Reno, OK is given below. An
illustration of the beginning and ending time of the tornado impact is shown in Figure 2.
5:37 PM - Tornado warning issued for storm along I-40 in Canadian County
5:57 PM - National Weather Service in Norman spots a dangerous rain-wrapped tornado two to three
miles south of I-40 southwest of El Reno.
6:22 PM - Large violent tornado reported by the National Weather Service in Norman just east of Hwy
81, near El Reno moving straight east at 25 mph
6:25 PM - Tornado emergency declared by National Weather Service in Norman for El Reno
6:27 PM - Storm chasers say El Reno tornado's damage path is a mile wide
6:56 PM - National Weather Service declares tornado emergency for Will Rogers Airport, Wiley Post,
Bethany, downtown Oklahoma City and north Moore
7: 09 PM - National Weather Service spotters see debris signature with tornado near Oklahoma City
Fairgrounds
7:28 PM - National Weather Service detects a new tornado just east of Will Rogers Airport
7:38 PM - From KFOR: Small tornado touchdown reported near 19th Street and Telephone Road in
Moore
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
4
Figure 2: Timing of Tornado Impact to El Reno, OK
(http://www.tulsaworld.com/article.aspx/Fridays_El_Reno_tornado_upgraded_to_EF5_widest_on_recor
d/20130605_11_A1_ULNSka613970 )
Confirmed Tornado Strikes
The NWS survey teams confirmed that five tornadoes occurred in the 31 May 2013 tornado outbreak,
the first occurring in Canadian County at 6:03 PM UTC and the last reported at 7:38 PM in Cleveland
County. The estimated path of three of the tornadoes are illustrated in Figure 3, one began near El Reno
and ended west of Yukon and then two in the South Oklahoma City area. The most dramatic damage
seen was that of the tornado traveling in the vicinity of El Reno, OK. Preliminary damage assessments
by the local NWS survey teams reported the storm to be an EF3, but after retrieving data from a mobile
Doppler radar close to the tornado, this rating was upgraded to an EF5, with peak wind speeds of 295
mph.
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
5
Figure 3: Preliminary Tornado Tracts of Three Independent tornadoes (Source:
http://localtvkfor.files.wordpress.com/2013/06/tracks.jpg)
The maximum path width of the tornado was determined to be 2.6 miles and the approximate length
was 16.2 miles, with the tornado appearing to be at its greatest intensity right before it reached any of
the heavily populated regions of El Reno, OK. At this time, 20 fatalities and over 240 injuries are
reported. Figure 4 displays a map where the first nine confirmed victims were found. A summary of the
locations and other significant data concerning each confirmed tornadoes is given in Table 1.
(http://www.tulsaworld.com/article.aspx/El_Reno_tornado_upgraded_to_EF5/20130604_100_0_TeNto
a585439 | http://kfor.com/2013/06/04/may-31-tornado-makes-history-largestef-5-on-record/ |
http://www.weather.com/news/tornado-central/storm-damage-friday-20130531)
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
6
Table 1: Preliminary Tornado Survey Results
(Source: http://www.srh.noaa.gov/oun/?n=events-20130531 )
Figure 4: Map of Locations of first nine confirmed victims (Source:
http://localtvkfor.files.wordpress.com/2013/06/may-31-tornado-death-map.jpg )
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
7
PREVIOUS TORNADOES IN EL RENO, OK
MAY 24 2011: At 3:50 PM CDT, the populated city of El Reno was struck by a devastating EF5 tornado
that resulted in 9 deaths and 181 injuries. This 1760 yard wide tornado moved east-northeast through El
Reno, creating a damage path more than 63 miles long, with peak winds greater than 210 mph. Similar
to the May 31, 2013 tornado, wind speed measurements from a mobile Doppler radar were used to rate
the tornado. The majority of the damaged buildings were one and two-story residential structures built
on concrete slab foundations, several mobile homes were destroyed, and a few commercial buildings
were badly battered. The May 24, 2011 and May 31, 2013 tornadoes are illustrate in Figure 5.
(http://www.srh.noaa.gov/oun/?n=events-20110524-tornado-b2 | http://newsok.com/oklahomatornadoes-8-dead-60-injured/article/3570916)
COMPARING MAY 20TH AND MAY 31ST OKLAHOMA TORNADOES
The evening of May 20th, 2013 Moore, OK was devastated by a 2 mile wide EF-5 tornado. It left a 17 mile
damage path and resulted in 24 fatalities. Although detailed information concerning the El Reno tornado
is not yet known, Moore was in the direct path of the tornado while the El Reno tornado followed a path
that circumvented the city proper. (http://kfor.com/2013/06/04/may-31-tornado-makes-history-largestef-5-on-record/)
Figure 5: May24, 2011(Red) May 31, 2013 (Blue) El Reno Tornado Track
[The yellow, and grey areas illustrate the populated regions, graying being densely populated]
(http://www.srh.noaa.gov/images/oun/wxevents/20110524/maps/tornado-b2-b3-whole.jpg ) 
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
8
BUILDING CONSTRUCTION IN EL RENO, OK
El Reno, OK has a population of approximately 17,510 persons, living in 6,752 homes
(http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?src=bkmk |
http://quickfacts.census.gov/qfd/states/40/4023700.html )
95% of the homes in El Reno were built before 2000. The complete distribution of home ages is
illustrated in Figure 7.
Figure 6: Comparing May 20th and May 31st Oklahoma Tornadoes
(http://www.tulsaworld.com/article.aspx/Fridays_El_Reno_tornado_upgraded_to_EF5_widest_on
_record/20130605_11_A1_ULNSka613970 )
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
9
0%
20%
40%
60%
80%
100%
120%
<1939 <1949 <1959 <1969 <1979 <1989 <1999 <2004 <Present
Year Built Cumulative Distribution of Homes
Figure 7: Distribution of Home Age in El Reno, OK
(http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?pid=ACS_11_5YR_DP04)
Observed Damages
Although detailed information is not yet known, reports obtained from local news agencies and social
media have indicated heavy damage to one technical training school, and a number of commercial
buildings and residential buildings.
The Canadian Valley Voc Tech School’s El Reno campus sustained heavy damage. The front of the main
building and all other out buildings on the campus were severely damaged. Before and after photos of
part of the campus are shown in Figures 8. It is not known at this time what the exact structural designs
for this school was but it has been reported that those present at the time of the storm found shelter in
the basement of one of the buildings on campus (Source: http://www.cvtech.edu/whats-new/cv-techworks-dispel-wind-tower-blade-reports).
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
10
(a) Voc Tech School’s Out Building
(before) (b) Voc Tech School’s Out Building (after)
Figure 8: Before and after photos of damage to Canadian Valley Voc Tech School, El Reno Oklahoma
(Images Courtesy of Google maps & http://www.news9.com/story/22475572/news-9-pilot-jimgardner-takes-aerial-look-of-tornado-damage-in-el-reno)
Damage to residential structures appears to be quite extensive, although no estimate as of yet has been
given as to the number of homes damaged or destroyed. A neighborhood south of I-40 sustained heavy
damage, as shown in Figure 9(b).
Using data available on Zillow.com, most of the homes within the damage path appear to have an
average age of 30 years, years of construction ranging from 1935 to 2009.
Figure 9(d) shows a mobile home, built in 1978, moved about 100 feet off its foundation and what’s left
of it scattered over Tiffany Lane. It was located near the centerline of the estimated tornado path. From
the photo it can be seen that this was a wood-frame home, but no information can be seen to indicate
the quality of the wall-to-foundation and roof-to-wall connections. Note that while this home was
completely swept off its foundation, homes in the background have damage varying from minor
sheathing loss to being completely leveled.
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
11
(a) Residential Buildings (before) (b) Residential Buildings (after)
(c) Aerial View of house built in 1978
(before) (d) Aerial View of house built in 1978 (after)
Figure 9: Before and after photos of damage to Residential Structures between S Manning Rd and S
Evens Rd
[(c) & (d) show extensive damage to a home at 4710 Tiffany Ln, El Reno, OK 73036]
(Images Courtesy of Google maps & http://www.news9.com/story/22475572/news-9-pilot-jim-gardnertakes-aerial-look-of-tornado-damage-in-el-reno)
Wind Hazard Damage Assessment Team
Engineering School of Sustainable Infrastructure and Environment
University of Florida
June 6, 2013
12
CONCLUSIONS
Our group is concerned regarding the upgrading of the EF-rating from EF-3 to EF-5, with apparently no
evidence of damage to support this on the ground. The reported use of mobile Doppler radar data on
peak wind speeds is we believe an inappropriate use of the rating – as it does not provide wind speeds
at the ground level where damage occurs. The guidelines for the Enhanced Fujita Scale states that, “The
technology of portable Doppler radar should also be a part of the EF Scale process, either as a direct
measurement, when available, or as a means of validating wind speeds estimated by the experts.”
However, as yet, the velocity profile of wind speeds in tornadoes cannot be predicted from tornado to
tornado with any degree of certainty. (Source: http://www.depts.ttu.edu/nwi/Pubs/FScale/EFScale.pdf).
We were also concerned that at least four motorists and four tornado storm chasers were among the
fatalities in this storm. One weather crew also suffered injuries. It is important for us to acknowledge
the unpredictable nature and strengths of these tornadoes and know that driving in a vehicle is not the
safest place to be. Much has been made about the evening weather forecaster of a local TV station who
advised listeners to leave their buildings, get into their cars and try to outrun the tornado. Such advice
is incorrect as it places many more persons at risk of injury and death, as they were on 31 May 2013,
stuck in bumper-to-bumper traffic on the south-bound lanes of Interstate I-35.


summarize everything into bullet points, and then if asked elaborate on them