<P> What at one time was thought to be the record holder for the longest tornado path is now thought to be the longest tornado family, with a track of at least 293 miles (472 km) on May 26, 1917 from the Missouri border across Illinois into Indiana . It caused severe damage and mass casualties in Charleston and Mattoon, Illinois . </P> <P> What was probably the longest track supercell thunderstorm tracked 790 miles (1,270 km) across 6 states in 17.5 hours on March 12, 2006 as part of the March 2006 tornado outbreak sequence . It began in Noble County, Oklahoma and ended in Jackson County, Michigan, producing many tornadoes in Missouri and Illinois . </P> <P> Officially, the widest tornado on record is the El Reno, Oklahoma tornado of May 31, 2013 with a width of 2.6 miles (4.2 km) at its peak . This is the width found by the National Weather Service based on preliminary data from University of Oklahoma RaxPol mobile radar that also sampled winds of 296 mph (476 km / h) which was used to upgrade the tornado to EF5 . However, it was revealed that these winds did not impact any structures, and as a result the tornado was downgraded to EF3 based on damage . However, another possible contender for the widest tornado as measured by radar was the F4 Mulhall tornado in north - central Oklahoma which occurred during the 1999 Oklahoma tornado outbreak . The diameter of the maximum winds (over 110 mph (49 m / s)) was over 5,200 feet (1,600 m) as measured by a DOW radar . Although the tornado passed largely over rural terrain, the width of the wind swath capable of producing damage was as wide as 4 mi (6.4 km). </P> <P> The F4 Hallam, Nebraska tornado during the outbreak of May 22, 2004 was the previous official record holder for the widest tornado, surveyed at 2.5 miles (4.0 km) wide . A similar size tornado struck Edmonson, Texas on May 31, 1968, when a damage path width between 2 to 3 miles (3.2 to 4.8 km) was recorded from an F3 tornado . </P>

Where did the widest tornado on record occur