The American Meteorological Society has released a preliminary version of its after-action report on the El Reno, Oklahoma, tornado, which killed noted storm chaser Tim Samaras, his son Paul and chase partner Carl Young. The result, even in dry, acronym-heavy academic language, manages to serve as both an enlightening and horrifying account of storm chasing's worst day.
A storm chaser who heeded the bad feeling in his gut and decided to hang back that day told me the tornado was "designed to kill storm chasers." This report indicates he's more right than he could have known. Doppler imaging pegged the tornado's width at 2.5 miles, the widest ever documented. But the main circulation was crawling with smaller tornadoes, some moving at speeds of 260 feet per second (177 mph), according to the report. The authors conclude, "it is likely that no clear direction to safety was apparent."
Samaras' Chevy Cobalt was traveling east down a dirt road with the tornado to his south. He almost certainly didn't know that the rain-shrouded vortex was hooking toward him, to the northeast, and that he had entered its circulation. The breathtakingly fast subvortex -- the tornado within a tornado -- is visible to the south in footage captured by fellow chaser Dan Robinson's rear dashboard cameras as he fled several hundred yards ahead of Samaras. The debris field created by Samaras' wrecked car, the report concludes, corroborates the footage, which shows the subvortex moving across the face of the larger tornado at about the time Samaras' headlights disappear. What's eerie is that the subvortex becomes stationary on the road, like it chose to stop right on top of them. After 20 seconds, it rotates back around to the south side of the tornado.
The shredded pieces of the car hook to the south then across the road to the northeast:
"The last sighting of the Samaras vehicle's headlights, the location of the trunk contents, and the location where the vehicle was discovered are consistent with it being transported initially southward by strong northerly flow on the west side of the sub-vortex, then roughly eastward about the south side of the vortex as the vortex remained quasi-stationary for about 20 (seconds). The vehicle could have covered the approximately (656-yard) path from starting to ending location during the 20 (second) period that the sub-vortex was quasi-stationary, if the vehicle was transported at a plausible speed of about (30 yards per second)..."
I have difficulty fathoming the violence implied in that paragraph.
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The rest of the report deals with how we quantify El Reno, which surprisingly can be pretty subjective. As we wrote a while back, the National Weather Service downgraded the tornado from an EF-5 to an EF-3. The scale is based on observable destruction, and little was damaged as it tracked through the remote, relatively featureless farm country.
Was El Reno a giant tornado populated with powerful subvortices? Or was it a rotating thunderstorm (a supercell) with small- to moderate-sized tornadoes swirling about one another? Either prospect is equally remarkable.
And what of its width? Two and half miles has been the widely accepted dimension, but if you measure wind speeds, the tornado could have been anywhere from three to 4.5 miles across. On the other hand, if you calculate its width by how much debris was lofted into the air, we may be talking about a mile and a quarter to nearly two miles in width.
You can read the preliminary version here. The authors are Joshua Wurman, Karen Kosiba and Paul Robinson with the Center for Severe Weather Research, and Timothy Marshall of Haag Engineering, a damage-path surveyor from Flower Mound whom I interviewed for our cover story on the tornado.