The reason this storm is being referred to as a ‘super tornado, is because this particular tornado is ‘so far,’ the largest (widest) tornado recorded in history (confirmed by damage assessment), and was a tornado with local measured EF5 wind velocities, according to multiple Doppler on wheels (DOW) measurements collected by tornado research teams lead both Dr. Howie Bluestein’s Oklahoma University (OU) Phased Array Radar, and by Dr. Joshua Wurman, multiple DOWs, and the Center for Severe Weather Research (CSWR).
Extracted: DOW 6 position scanning the El Reno tornado, May 31st, 2013, Courtesy: CSWR Preliminary Results from the ROTATE-2013 Season, Report (2013). See AMS report link at bottom of page.
Just like hurricane Sandie got the notorious title: ‘Super storm Sandy,’ the El Reno tornado of May 31, 2013, has picked up the moniker as a super tornado of the new millennium.
What is most remarkable about this gigantic tornado is that it was successfully captured by DOW field research teams, and that direct research data allows society to look into what is termed an ‘historic’ tornado. This tornado was originally given an EF5 rating by NWS, based on verified DOW wind velocity measurements taken by multiple scientific field research teams, and was later down-graded by the NWS, because the damage survey ‘mostly’ produced evidence of EF3 damage.
New perplexing and amazing data about the May 31st, 2013, El Reno tornado has now surfaced at the recent American Meteorological Society (AMS), 36th Conference on Radar Meteorology (16-20 September, 2013), in Breckenridge, Colorado. In particular, a co-authored report by CSWR, containing data about a number of tornadoes studied this spring (Preliminary Results from the ROTATE-2013 Season), with the hint that even more intriguing information will be forthcoming in future papers in 2014. New startling facts have emerged which shed even more focused light on this historic El Reno tornado event. This preliminary data research report was co-authored by: Dr. Joshua Wurman, Dr. Karen Kosiba and Paul Robinson of CSWR, and with the help of Tim Marshall P.E.,Haag Engineering.
I had to read this paper several times to understand the particular significance of research findings presented in this document and the associated AMS published poster presentation.
What was immediately apparent was that in fact, the El Reno multi-vortex tornado complex did have a number of DOW validated EF5 scale sub-vortices below the large parent tornado that also had elevated EF5 scale winds, within the parent mesocyclone complex. The orbit of the EF5 sub vortices were in “trochoidal-like patterns”1, almost as if drawn by hand attempting to create connecting circles on Spirograph or an Etch-a-sketch (See slideshow picture1).
“Trochoidal-like pattern”3 to tornado core flow movement (highlighted in yellow). Courtesy: CSWR Preliminary Results from the ROTATE-2013 Season, Report (2013). See AMS report link at bottom of page.
From a tornado chaser perspective this is storm tracker hell, as taking a safe path in tracking such a wobbling and expanding tornado is nearly impossible. The mesocyclone got so low to ground at certain points, that in some cases, it too made contact with the ground producing rotating tornadic winds on an enormous scale during several points of the El Reno tornado genesis.
Here is where data, if interpreted correctly produces some questions. Many of the near-ground EF5 velocity measurements were documented within 100-114 meters in elevation. To give perspective, 300ft is about 70ft lower than the top of the popular Bastille Crack climb in El Dorado canyon that hangs over the road. That is incredibly low. Or if you are not familiar with mountain cliff terrain, 300ft is roughly the height of a 30 story building. In any major city, a thirty story building hardly registers against the skyline. If you then add a parent tornado of greater than a mile in diameter rotating above with EF5 velocities and with a low base, in some cases below 900ft, coupled with high surface dew points exceeding 70 and with significantly high thermal energy, there exists a hydraulic fluid conduit near the surface that makes for a “large tornado / multiple-vortex mesocyclone (MVMC)” that in some points during genesis was at near ground levels. For those tracking the El Reno super tornado, and lucky enough to survive, this is no real surprise.
Here is the issue, ground measurement of EF5 sub-vortices is incontrovertible evidence when coupled with an EF5 damage assessment. However, with DOW-obtained EF5 measurements, in some cases not meeting the particular criteria of the Saffir-Simpson measured 3-second wind gust criteria, then such useful data with only a limited EF3 a correlated damage estimate, the result leaves many questions. Confounding the process of damage assessment occurs when a powerful tornado, such as the El Reno EF5 travels across open range lands, as NWS presently has scant criteria to measure tornado damage over such terrain. I refer to the El Reno tornado as EF5, at this moment, because for a period of time the National Weather Service (NWS) did list the El Reno tornado as an EF5, until subsequently downgraded based on an EF3 damage survey results. However, for sake of this discussion, the brief now validated EF5 sub-vortices and EF5 parent tornado that moved over rangelands and open fields in a “trochoidal-like pattern,”2 (Wurman, CSWR 2013) the concept of what qualifies a tornado of a particular strength as a resulting EFx, is difficult to determine. To add another layer of difficulty to the NWS damage assessment process of the El Reno super tornado, were two additional factors. The first was the strange orbital movement of this tornado path, and then the erratic jog the parent tornado took during genesis that made this east-southeastern mover, take a turn northeastward while simultaneously expanding in width.
For Tim Samaras, a highly skilled and well regarded tornado research scientist, this particular erratic tornado behavior was an unanticipated lethal move. Yet, Tim Samaras himself may have provided the last bit of tangential evidence, where damage met EF5 sub-vortices that align with the El Reno core flow track.
In looking back at the recent AMS published “Preliminary Results from the ROTATE-2013 Season,” new information has come to light, and it is highly recommended to read the ROTATE-2013 report. By reviewing the latitude and longitudinal positional tracks of the tornado core flow (See slideshow), and noting where the Tim Samaras tornado research vehicle GPS position was initially now known to be struck by the known EF4+ sub-vortices below and within the parent EF5 core flow region, where the vehicle was then dismembered ( leaving the heavy engine block near the collision point of impact), and the tornado carried the remaining lighter skin of the research vehicle approximately 1,800 additional feet, during an approximate 20 second period of time, until the rest of the remaining damaged vehicle finally came to rest in the general direction of the trajectory region of the core flow path.
Tim himself provides the last bit of evidence about the El Reno super tornado behavior. When the El Reno tornado crossed highway 81 and struck Tim Samaras’s vehicle that location was primarily open fields with little possibility to obtain additional confirmatory structural damage estimates, other than the destroyed research vehicle itself.
Here is a remaining question, according to NWS damage survey criteria, a chucked vehicle is not considered a particular measure of merit for determining EF strength. The reason is that a vehicle is not typically anchored to the ground, such as is the case with the foundation of a house, where sheared bolts and pulverized pre-stressed concrete can give a wind force translation measurement of specific EF strength. However, there where many tornado trackers on the May 31st El Reno tornado with GPS position and time-stamped footage of the tornado from many angles and proximal distances obtained by other chase vehicles. If forensic review of the now known position of the Samaras vehicle, as debris, where identified in such other footage, and cross-correlated against the DOW EF5 velocity measurements, and the vehicle debris was within close proximal longitude, latitude, and elevation to the same DOW scan level, then the combination of validated Doppler data, along with the movement of vehicle debris through frames would help answer the EFx question. I can only guess Dr. Ted Fujita himself, the pioneer of the EF-scale, would applaud use of DOW direct measurement, damage assessment, and precise image telemetry to determine tornado velocity. The particular detail of using a Hurricane-based Saffir-Simpson Wind Scale determining damage based on a 3-second gust in a tornado assessment, while useful, may not be entirely an accurate measurement for a tornado for two reasons. First, tornado wind-torque force is not a straight line phenomena, and secondly, at wind velocities in the 300 plus mph scale range, the force applied is logarithmic, meaning the energy released by an EF5 sub vortice against the Samaras research vehicle was more akin to an explosive blast effect or collision than a typical hurricane-type lower scale straight line sustained wind gust.
Tornado researchers suspect even more will be reveled about the El Reno super tornado over the coming years, and numerous lessons-learned will be incorporated into storm tracker vehicle safety margins, buffer zones, better sheltering, and a likely change may yet occur in NWS policies about using validated DOW data, when available, in determining EF-scale of a particular tornado, as was the case on the highly publicized Goshen, Wyoming tornado of 2009.
For me it is great to see when society at large can take validated scientific data into consideration to make reasoned policy decisions that helps humanity better survive the extremes of nature’s fury. Why this is important is because the El Reno super tornado was heading on a direct path toward Oklahoma City, and just after the tornado lifted the powerful mesocyclone did pass over downtown Oklahoma. Knowing this fact allows Federal government and State planners an opportunity to develop stronger structures, better shelters, and optimize ways to manage a pending disaster of such magnitude. Fortunately, this tornado just became a near miss to a major populated area.
In summary, as paraphrased, new data indicates this tornado produced short term EF4+ and EF5 strength near ground sub-vortices, had a rotational maximum with fluctuating lower velocity winds approximately extending outwards up to 2.15 miles on either side of the main core flow region, and did mostly EF3 damage to structures within the perimeter of the enormous ground raking tornado collar cloud.
1-3 “Preliminary Results from the ROTATE-2013 Season, Joshua Wurman, Karen Kosiba, and Paul Robinson, Center for Severe Weather Research (CSWR), Boulder, Colorado, Tim Marshall, Haag Engineering (2013), American Meteorological Society (AMS), 36th Conference on Radar Meteorology (16-20 September, 2013), Breckenridge, Colorado
“187 Preliminary Results from the ROTATE-2013” (Radar Observations of Tornadoes and Thunderstorms) experiment, https://ams.confex.com/ams/36Radar/webprogram/Paper229323.html (Monday, 16 September 2013)
“5/31/13 Widest Ever (2.6 Miles Wide) El Reno Tornado and Oklahoma City Tornadoes,” Basehunters, http://www.youtube.com/watch?v=ZSlAF9SD41k&list=TLcjpXCeUJhbPzvPUbHU3quk… (May 31, 2013) published June 2, 2013
“The Role of Multiple Vortex Tornado Structure in Causing Storm Researcher Fatalities, Joshua Wurman, Karen Kosiba, Paul Robinson, Tim Marshall, American Meteorological Society (AMS), 10.1175/BAMS-D-13-00221.1, http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-13-00221.1