Tornadoes are among nature’s most powerful and destructive phenomena, capable of unleashing immense force upon the landscape. These rotating columns of air, extending from a thunderstorm to the ground, can cause widespread devastation in their path. Among these formidable storms, the most extreme category, known as F5 or EF5 tornadoes, represents the pinnacle of intensity and destructive potential.
Understanding Extreme Tornadoes: F-Scale vs. EF-Scale
The intensity of tornadoes was historically assessed using the Fujita Scale, or F-Scale, developed by Dr. Tetsuya Fujita in 1971. This scale classified tornadoes from F0 to F5 based on the damage they inflicted on structures and vegetation, with F5 representing the most severe damage. The F-Scale also estimated wind speeds, with F5 tornadoes estimated at 261-318 mph, though these were not direct measurements.
The National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) introduced the Enhanced Fujita Scale, or EF-Scale, in 2007 to improve tornado classification. This updated scale refines the damage assessment process by using 28 specific “damage indicators” and considering the quality of construction. The EF-Scale provides more accurate estimates of wind speeds associated with observed damage, aligning them more closely with engineering studies. While the method of rating changed, previously documented F5 tornadoes retain their F5 classification in the historical record.
The Rarity of F5 Tornadoes
F5 and EF5 tornadoes are exceptionally rare events in the United States. Since 1950, a total of 59 tornadoes have been officially rated as F5 or EF5. Fifty of these were classified as F5s under the original Fujita Scale, occurring between May 1953 and May 1999. Following the implementation of the Enhanced Fujita Scale in 2007, nine tornadoes have been rated as EF5.
The most recent EF5 tornado to strike the U.S. occurred on May 20, 2013, in Moore, Oklahoma. This extended period without an EF5 tornado marks the longest such “drought” in recorded history since 1950.
Notable F5 Tornadoes and Their Legacy
Several F5 and EF5 tornadoes have left lasting impacts. The Tri-State Tornado of March 18, 1925, though occurring before the F-Scale was devised, is retrospectively considered an F5 and remains the deadliest single tornado in U.S. history, killing 695 people. It carved a devastating path across Missouri, Illinois, and Indiana. The Waco, Texas, tornado of May 11, 1953, holds the distinction of being the first tornado officially rated F5, resulting in 114 fatalities.
The May 3, 1999, Oklahoma tornado, which struck areas including Moore, was an F5 that produced some of the highest wind speeds ever recorded on Earth, with a Doppler On Wheels unit measuring 318 mph a few hundred feet above the surface. More recently, the EF5 tornado that devastated Joplin, Missouri, on May 22, 2011, caused 158 fatalities, making it the deadliest single tornado in the U.S. since 1947.
Why F5s Are So Infrequent
The formation of an F5 or EF5 tornado requires a highly specific and rare confluence of atmospheric conditions. These tornadoes typically develop from powerful supercell thunderstorms, characterized by a persistent rotating updraft called a mesocyclone. For such an intense tornado to form, the mesocyclone must be particularly robust and well-organized.
A significant amount of warm, moist air near the ground fuels strong updrafts, while cooler, dry air aloft creates atmospheric instability. Strong wind shear, the change in wind speed or direction with height, is essential to tilt and intensify the rotation within the storm. While many tornadoes form under favorable conditions, the precise combination of these factors needed to produce an F5 or EF5 tornado is exceptionally rare.