Largest Tornado on Record: the May 31 El Reno, OK EF-5 Tornado

The largest tornado in recorded history was Friday's May 31, 2013 EF-5 tornado in El Reno, Oklahoma, the National Weather Service in Norman, Oklahoma announced on Tuesday. The EF-5 re-classification was based upon Doppler radar data taken by Oklahoma University's mobile RaXPol radar. According to comments made by tornado researcher Rick Smith at a press conference today, the mobile radar was positioned on top of an overpass, and recorded winds close to the surface of up to 295 mph in satellite suction vorticies that orbited the large, main vortex. The large, main vortex had EF-4 winds of 185 mph, and the satellite suction vortices moved across the fields at that speed, and rotated on their own at speeds of up to 110 mph, giving a combined wind speed of up to 295 mph in some of the satellite vortices. It's no wonder that so many storm chasers got in trouble with this tornado, since these suction vortices moved as speeds of up to 185 mph towards them as the tornado rapidly expanded into the largest on record. The tornado killed tornado scientist Tim Samaras and his two chase partners, Paul Samaras and Carl Young, and also killed an amateur storm chaser, Richard Charles Henderson. The 295 mph winds of the El Reno tornado rank second only to the world-record 302 mph (135 m/s) winds recorded in the Moore, Oklahoma tornado of May 3, 1999. However, the Moore tornado's winds were measured at an altitude of 105 feet (32 meters), so the winds near the surface may have been higher in the El Reno tornado.


Figure 1. Path of the May 31, 2013 El Reno, Oklahoma tornado from the National Weather Service in Norman, Oklahoma. Note how the tornado began moving directly down I-40 as it headed towards Oklahoma City; had the tornado maintained its EF-5 strength and moved down I-40 into Oklahoma City, where traffic was bumper-to-bumper due to people trying to flee, the greatest tornado disaster in U.S. history would have resulted.


Video 1. The May 31, 2013 El Reno, Oklahoma EF-5 tornado as filmed by storm chasers Justin Hoyt and Stephen Barabas, another team of chasers that were in extreme danger from the tornado. Their description: "The LONGER, INCREDIBLE WAY TOO CLOSE video of the multivortex tornado near El Reno, Oklahoma on May 31st. This beast quickly turned onto us and grew into an over 2.6 mile wedge, the largest on record. After the easy escape from the multivortex, we ended up dropping south right into the damage path of the monster, getting caught up in its outer circulation. The dangerous aspect was that chasers were positioned all over the road and backed up in a panic instead of immediately turning around." Warning: foul language, including one F-bomb. A more detailed account of the chase is here.

Previous record largest tornado: 2.5 miles in diameter
The previous official record for the widest tornado belonged to the EF-4 Wilber - Hallam, Nebraska tornado on May 22, 2004, which had a damage path up to 2.5 miles wide. However, NOAA's Storm Data publication documents that the EF-3 Edmonson, Texas tornado of May 31, 1968 had a damage path width between 2 and 3 miles (3.2 and 4.8 km) wide. In addition, Doppler radar measurements indicate that the May 4, 1999 Mulhall, Oklahoma EF-4 tornado--which thankfully passed mostly over farmland--would have caused damage over a path 4 miles wide at its peak size, had it encountered a built-up area.


Figure 2. Damage swath of the Wilber - Hallam, Nebraska F-4 tornado of May 22, 2004 was up to 2.5 miles wide, making it one of the largest tornadoes on record.

Wunderground has large 2 Mb animations of the high-resolution radar reflectivity and Doppler velocity Level II radar data, with the damage path of the May 31, 2013 El Reno tornado overlaid.

Jeff Masters