May–June 1917 tornado outbreak sequence
Tornado damage in Mattoon, Illinois, on May 26
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| Type | Tornado outbreak |
|---|---|
| Duration | May 25–June 1, 1917 |
| Tornadoes confirmed | ≥ 73 |
| Max rating1 | F5 tornado |
| Duration of tornado outbreak2 | 8 days |
| Damage | > $6.88 million (1917 USD); >$129 million (2017 USD) |
| Casualties | ≥ 383 fatalities, unknown injuries |
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1Most severe tornado damage; see Fujita scale 2Time from first tornado to last tornado |
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1Most severe tornado damage; see Fujita scale
The 1917 May–June tornado outbreak sequence was an eight-day tornado event, known as a tornado outbreak sequence, that killed at least 383 people, mostly in the Midwestern and parts of the Southeastern United States. It was the most intense and the longest continuous tornado outbreak sequence on record, with at least 73 tornadoes including 15 that were analyzed to have been violent (F4–F5) based upon reported damage. The deadliest tornado of the entire sequence produced a 155-mile (249 km) track across Illinois, killing 101 people and devastating the towns of Charleston and Mattoon along with small farming communities. Once believed to have traveled 290-mile (470 km) cross Illinois and into Indiana, it is now assessed to have been a tornado family of four to eight separate tornadoes.
A series of low-pressure areas affected the Central and Eastern United States between May 25 and June 1, 1917. The first of these developed by May 25 east of the Rocky Mountains in eastern Colorado. By 7:00 p.m. CST/0100 UTC that day, it intensified to 29.45 inches of mercury (997.3 mb) with temperatures rising at or above 70 °F (21.1 °C) over most of Kansas. The next day, the low-pressure system deepened further into the morning, eventually centering near Yankton, South Dakota, about 7 a.m. CST/1300 UTC. Upon weakening to about 29.55 inHg (1,000.7 mb) in the evening and centering near Des Moines, Iowa, the low was followed by another surface low which formed over the Texas Panhandle and moved northeast. This second low passed near Oklahoma City, Oklahoma, on the morning of May 27 and approached the St. Louis, Missouri, area in the evening. On May 30, yet another low of about 29.5 inHg (999.0 mb) by 7 p.m. CST/0100 UTC moved northeast from near Concordia, Kansas, to Des Moines.
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