When was the last EF5 tornado?
The most extreme tornadoes have winds over 200 mph and can measure over a mile wide, and it has been over a decade since the last EF5 has struck the United States.
Experts show AccuWeather how they survey and document damage to determine the wind speed and path of destructive tornadoes.
Tornadoes are among the strongest and deadliest types of weather, capable of destroying entire neighborhoods in minutes. However, the most powerful tornadoes, classified as EF5, make up less than 1% of all tornadoes in the United States, and it has been 12 years since one touched down.
There have been many powerful tornadoes that have carved deadly paths across the U.S. in recent years, but none have hit with the ferocity of an EF5.
Moore, Oklahoma, tornado May 20, 2013
The most recent EF5 tornado in U.S. occurred on May 20, 2013, when a devastating twister barreled through Moore, Oklahoma, killing 24 and injuring hundreds more. The mile-wide tornado devastated several neighborhoods south of Oklahoma City with winds of 210 mph—the second time an EF5 hit Moore in the span of 14 years.
It was on the ground for roughly 20 miles and hit several neighborhoods, including a housing complex in Westmoor, the Plaza Towers Elementary School, the Moore Medical Center, and Highland East Junior High School.
Just 11 days later, another catastrophic tornado touched down in Oklahoma, hitting 35 miles northwest of Moore in El Reno. This was the widest tornado on record at 2.6 miles across, but it was ultimately rated an EF3.
How are tornadoes rated?
Tornadoes are rated on the Enhanced Fujita scale, an adaptation of the original Fujita scale, created by Dr. Tetsuya “Ted” Fujita in 1971. After a tornado occurs, a survey team inspects the damage. Based on the assessment, experts can then estimate the peak winds of the tornado, which determines the rating.
The weakest are EF0s with winds under 85 mph, and they can cause minor damage to buildings and cause weaker trees to topple. If a tornado moves over an open area, such as a field, and there is no damage that can be surveyed, it is called an EF-unknown (EFU).
EF5 is reserved for monstrous tornadoes with winds over 200 mph, strong enough to blow the bark off trees, rip up pavement and blow entire buildings off their foundations.
There have been 59 tornadoes rated either F5 or EF5 in the U.S. since 1950, according to NOAA. This accounts for 0.08% of all tornadoes in that time span.
EF5 tornado 'drought'
It has been 12 years since a tornado was given an EF5 rating, the longest stretch without such a powerful tornado in the U.S. since the 1950s.
A study published in the Bulletin of the American Meteorological Society in January investigated the current drought in EF5 tornadoes, and identified several factors behind the recent trends.
"The EF scale can be somewhat subjective and hasn't been applied consistently over the years," AccuWeather Meteorologist and Digital Producer Jesse Ferrell said. "When we moved to the new EF scale in 2008, the wind speeds to confirm an F5/EF5 tornado changed from 200 to 201 mph, but damage indicators which validate the wind speeds did not change."
Additionally, one of the indicators of an EF5 tornado is a home being swept clean from its foundation, but changes to building codes in recent years has made it harder for powerful tornadoes to cause such damage, Ferrell added.
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