In the United States, a night-time F5 tornado strikes the small city of Udall, Kansas as part of a larger outbreak across the Great Plains, killing 80 and injuring 273. It is the deadliest tornado to ever occur in the state and the 23rd deadliest in the U.S.

The Fujita scale, or Fujita–Pearson scale, is a retired 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.