The F4-strength St. Louis–East St. Louis tornado hits in St. Louis, Missouri, and East St. Louis, Illinois, killing at least 255 people and causing over $10 million in damage.

The Fujita scale, or Fujita–Pearson scale, is a scale for rating tornado intensity, based primarily on the damage tornadoes inflict on human-built structures and vegetation. The official Fujita scale category is determined by meteorologists and engineers after a ground or aerial damage survey, or both; and depending on the circumstances, ground-swirl patterns, weather radar data, witness testimonies, media reports and damage imagery, as well as photogrammetry or videogrammetry if motion picture recording is available. The Fujita scale, named for the meteorologist Ted Fujita, was replaced with the Enhanced Fujita scale (EF-Scale) in the United States in February 2007. In April 2013, Canada adopted the EF-Scale over the Fujita scale along with 31 "Specific Damage Indicators" used by Environment Canada (EC) in their ratings.

The 1896 St. Louis–East St. Louis tornado was an extremely deadly, powerful and catastrophic tornado that caused severe damage to downtown St. Louis, Missouri, East St. Louis, Illinois, and surrounding areas on Wednesday, May 27, 1896, at around 5:00 pm. One of the deadliest and most destructive tornadoes in U.S. history, this tornado was the most notable of a major tornado outbreak sequence across the central United States which produced several other large, long-track, violent tornadoes and continued across the eastern United States the following day. The St. Louis tornado killed at least 255 people, injured over a thousand others, and caused more than $10 million in damage in about 20 minutes. More than 5,000 people were left homeless and lost all of their possessions. The hardest-hit areas of the city were the fashionable Lafayette Square and Compton Heights neighborhoods, as well as the poorer Mill Creek Valley. It remains the third-deadliest tornado in United States history.

St. Louis is an independent city in the U.S. state of Missouri. It lies near the confluence of the Mississippi and the Missouri rivers. In 2020, the city proper had a population of 301,578, while its metropolitan area, which extends into Illinois, had an estimated population of over 2.8 million. It is the largest metropolitan area in Missouri and the second-largest in Illinois. The city's combined statistical area is the 20th-largest in the United States.