Remembering TWISTEX

 The May 31, 2013 El Reno tornado is considered one of the most powerful tornadoes to hit the midwest, crossing US-81. With the highest width of 2.6 miles, it was recorded by several storm chasers, and among them, was the group TWISTEX (Tactical Weather-Instrumented Sampling in/near Tornadoes Experiment), which was founded and led by Tim Samaras. The crew at the time of El Reno consisted of Tim Samaras, Paul Samaras and Carl Young. A brief summary of the events is as follows. At around 6 pm, the development of a tornado wall cloud was imminent, and at 6:03 pm, the ground circulations coincided and a tornadic system of multiple sub-vortices and circulations had developed south of El Reno. With increasing intensity (which initially categorized the tornado to EF3), the system developed over 2.6 miles, and over a span of 25 minutes had a course across the Canadian County, OK. The exact categorization of the tornado is controversial, and is typically associated to the EF5 scale. 

One of the characteristics that the El Reno tornado is infamously associated with is that of quick course changing. For instance, the tornado changed directions quickly and cut across the I-40, and would go on for a total span of $\sim $ 40 minutes, stretching over a span of around 17 miles. Another prominent characteristic attributed to El Reno is that the usual clear inside the cell of precipitations around a tornado was not present, and rather the outermost circulations of the tornado itself was a cell of precipitation. Unfortunately, the TWISTEX team was not travelling in their usual chasing-suited heavy lined vehicle, but rather in a Chevrolet with little modifications to suit it to the chase, and some of the first casualties of El Reno was that of Tim Samaras, Paul Samaras, and Carl Young. In Reed Timmer's video of the same tornado [1, 2], the Dominator 2's hood was badly damaged by overthrown lines, and it is suggested that had it not been that they stopped due to the overthrown lines on the road, they would have likely run into the same abrupt-direction changing incident that claimed TWISTEX. While usually the vehicles would be less susceptible to such situations while intercepting from the weaker side, the internal sub-vortices impacted the team. I recommend the paper by NOAA on the aerial survey of the El Reno tornado [3].

Associated to this mesmerizing but dangerous tornado was also the characteristic ``walking dead man" vortices, which can be seen forming and dissipating in the footage of the El Reno tornado [4]. 

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References

[1] Reed Timmer et al, Tornado Chasers S2E11: Nemesis, Part 1. Tornado Chasers, S2 Episode 11: "Nemesis, Part 1" 4K [May 31, 2013]

[2] Reed Timmer et al, Tornado Chasers S2E12: Nemesis, Part 2. Tornado Chasers, S2 Episode 12: "Nemesis, Part 2" 4K [May 31, 2013]

[3] Wakimoto et al, Monthly Weather Review -NOAA. Aerial Damage Survey of the 2013 El Reno Tornado Combined with Mobile Radar Data. Aerial Damage Survey of the 2013 El Reno Tornado Combined with Mobile Radar Data [2016]

[4] Markus Pfister, Multivortex-Tornado south of El Reno, May 31, 2013