The El Reno tornado of May 31, 2013 broke a record no other tornado has since matched: at its peak it was 2.6 miles wide — the widest tornado ever recorded. It also killed three professional storm chasers, including Tim Samaras, his son Paul Samaras, and Carl Young of TWISTEX — the first professional chasers ever killed by a tornado.
Mobile Doppler radar operated by researcher Howard Bluestein documented the tornado's continuous rotation over an area 2.6 miles across — greater than the previous record set by the Hallam, Nebraska tornado of 2004. At its widest, the tornado covered nearly the entire distance between rural county roads.
The tornado also produced radar-measured winds of 296 mph, one of the highest values ever recorded in Earth's atmosphere and comparable to the 1999 Bridge Creek reading of 301 mph.
Despite the radar-measured EF5-caliber winds, the National Weather Service rated the tornado EF3 based on damage indicators along its path. The tornado formed over open rural country west of El Reno and largely stayed there — encountering few well-built structures capable of documenting its full intensity. The EF Scale is a damage-based rating; a tornado that does not strike a strong structure cannot be rated based on peak wind alone.
This event is often cited by tornado researchers as a case study for the limitations of damage-based ratings. Some meteorologists refer to El Reno 2013 informally as a "hidden EF5."
The tornado touched down at 6:03 PM CDT approximately 8 miles west of El Reno. Over the next 40 minutes it exhibited highly unusual behavior:
Storm chaser and severe weather researcher Tim Samaras — founder of the TWISTEX (Tactical Weather-Instrumented Sampling in/near Tornadoes Experiment) program — was intercepting the tornado to deploy scientific probes when the tornado unexpectedly turned toward his vehicle and rapidly accelerated. He, his son Paul Samaras, and colleague Carl Young were killed. They remain the only professional storm chasers ever killed by a tornado in the field.
The Weather Channel meteorologist Mike Bettes and his crew narrowly survived after their vehicle was thrown by a sub-vortex.
The El Reno tornado led to significant changes in storm chaser safety practices, including greater emphasis on longer standoff distances, better forecasting of erratic behavior, and improved communications between chasers and NWS forecasters. It also reignited debate about whether the EF Scale should incorporate radar-measured winds when high-quality mobile Doppler data are available.
Just 11 days earlier, the same corridor of central Oklahoma had been struck by the deadly Moore, OK EF5 tornado — making late May 2013 one of the most intense two-week periods in modern US tornado history.
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