The U.S. central plains region -- nicknamed Tornado Alley -- suffers the highest frequency of tornadoes in the world [source: Tarbuck]. Many of these twisters leave death, injury and destruction in their wake, but one stands in a class by itself.
Sweeping out from southeastern Missouri on March 18, 1925, the Tri-State Tornado careened across the southern tip of Illinois before dissipating in lower Indiana. Remarkably, these three locales lie 219 miles (352 kilometers) apart, and the tornado traveled this distance in just three and a half hours [source: SEMP].
Typical tornadoes measure 500 to 2,000 feet (150 to 600 meters) wide and move at a speed of about 30 mph (45 kph). Generous estimates suggest they travel an average of 6 miles (10 kilometers) before petering out [source: Tarbuck]. The Tri-State Tornado achieved an average speed of 62 mph (100 kph) and topped out at 73 mph (117 kph). It covered more than 36 times as much ground as an average tornado. Some eyewitnesses reported its path as nearly a mile wide [source: NOAA].
Scientists today wonder if the Tri-State Tornado instead might have been a family of tornadoes spawned by a massive supercell storm, which would account for both its extremity and for the remarkably straight path it followed for 183 of its 219 miles [source: NOAA].
All told, the EF5 storm killed 695 people, 234 of whom lived in the town of Murphysboro, Ill., thereby setting the grim record for the most fatalities incurred by a tornado in a single U.S. city. In total, 2,027 people sustained injuries from the tornado's passage, and 15,000 homes were destroyed. Entire towns were obliterated [source: SEMP].
Next, let's look at a more recent storm that the world won't soon forget.