Tornado outbreak sequence of May 21–26, 2011
The tornado outbreak sequence of May 21–26, 2011 was one of the largest tornado outbreaks on record which affected the Midwestern and Southern regions of the United States. Most of the tornadoes developed in a corridor from Lake Superior southwest to central Texas; isolated tornadoes occurred in other areas. An especially destructive tornado destroyed one-third of Joplin, Missouri, resulting in 158 deaths and over 1,000 injuries. The Joplin tornado is the deadliest in the U.S. since April 9, 1947, when an intense tornado killed 181 in the Woodward, Oklahoma area. Tornado-related deaths also occurred in Arkansas, Kansas, Minnesota, and Oklahoma. Overall, the tornado outbreak resulted in 184 deaths, 6 of those non-tornadic, making it second only to the 2011 Super Outbreak as the deadliest since 1974, and the second costliest tornado outbreak in U.S. history behind that same April 2011 outbreak, with insured damage estimated at $4–7 billion.
2011 Joplin tornado
In 2013, the American Society of Civil Engineers published a study disputing the tornado's initial EF5 rating, based on surveying damage on over 150 structures within a six mile segment of the storm's path. According to the report, over 83 percent of the damage was caused by wind speeds of 135 miles per hour or less, the maximum wind speed of an EF2 tornado. An additional 13 percent was caused by EF3 wind speeds, and 3 percent was consistent with EF4 winds. The study found no damage consistent with wind speeds over 200 miles per hour, the minimum threshold of an EF5 tornado. Researchers concluded that the inability to find EF5 damage was due to the absence of construction standards that were able to determine the necessary wind speeds. Bill Colbourne, a member of the engineering team that surveyed the damage, declared that "a relatively large number of buildings could have survived in Joplin if they had been built to sustain hurricane winds."