Oklahoma Tornado Is Nation's Strongest In Over A Year, NWS Says

A​ destructive Oklahoma tornado Saturday was the nation's strongest in just over a year.

A National Weather Service damage survey team rated the tornado that raked through parts of Marietta, Oklahoma, on the night of April 27 an EF4 with estimated peak winds up to 170 mph. This upgrade in the EF-scale rating was due to damage sustained at the Dollar Tree Warehouse and a retail store in the town after consultation with an engineer, according to NWS-Norman warning coordination meteorologist Rick Smith.

The tornado killed one person along its 27-mile-long path from the west side of Marietta to near Dickson, in southern Oklahoma, according to the National Weather Service.

"Violent tornadoes": While all tornadoes are capable of damage, meteorologists use the term "violent tornadoes" to refer to those rated EF4 or EF5, the highest two ratings on the Enhanced Fujita scale.

What makes these most intense tornadoes — with estimated winds of 166 mph or more — so dangerous is their capability of devastating damage: tossing and crushing vehicles, leveling well-constructed homes and even sweeping foundations clean. (Note: The Fujita (F) scale was replaced by the Enhanced Fujita (EF) scale in February 2007. Wind speeds associated with each category were reduced, but the general type of damage expected was not changed.)

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Strongest in over a year: This was the nation's first EF4 tornado in just over a year. According to tornado historian Thomas Grazulis, that was the third longest stretch without an F/EF4+ tornado dating to 1871.

Only two violent tornadoes occurred in 2023. Both of them - Rolling Fork, Mississippi and Keota, Iowa - occurred in late March.

T​he March 24, 2023, EF4 tornado in Mississippi demolished some homes, leaving just piles of debris on concrete slabs, mangled and debarked trees, and scoured the ground, leaving utility poles snapped near the ground covered in 1 to 2 inches of mud, according to the National Weather Service damage survey.

T​he few: These tornadoes are, thankfully, pretty rare. This century, the U.S. has averaged only 5 to 6 violent tornadoes per year, about 0.5% of the nation's total.

In 2018, there were no EF4 or EF5 tornadoes anywhere in the U.S. It was the only year without a single violent tornado dating to 1950.

There hasn't been a tornado rated EF5 in the U.S. since the Oklahoma City/Moore tornado on May 20, 2013.

Almost 90% of tornadoes from 2000 through 2022 were weak — rated F/EF0 or F/EF1 — but they're still capable of light to moderate damage to trees and homes, and significant damage to mobile homes.

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T​he deadly: From 2000 through 2023, the most recent year in which finalized tornado death counts are available from NOAA's Storm Prediction Center, this tiny fraction of tornadoes was responsible for roughly half of all U.S. tornado deaths.

The death toll from these 126 violent tornadoes (850 lives) exceeded the death toll from the other 27,317 tornadoes combined (820 lives). Put another way, each F/EF4 tornado killed an average of four or five people, while F/EF5 tornadoes killed an average of 37.

Spring is peak time: We examined the 646 violent tornadoes in NOAA's database from 1950 through 2023 to see if there was a peak time of year.

We found a broad peak from April through early June, during which 59% of violent tornadoes occurred.

• April 2011 Super Outbreak: 15 violent tornadoes on April 27 alone, including four rated EF5
• May 3, 1999, Plains Outbreak: First F5 on record to hit Oklahoma City metro; F4 strikes southern side of Wichita, Kansas
• April 1974 Super Outbreak: 30 violent tornadoes, including six rated F5
• April 1965 Palm Sunday Outbreak: 22 violent tornadoes

The 25 deadliest tornadoes on record in the U.S. all occurred from mid-March through June.

Why spring: Spring typically provides a prime overlap of ingredients in the southern and central U.S. needed to generate the intense, rotating supercell thunderstorms that can spawn violent tornadoes.

Increasingly warm, humid air streaming northward out of the Gulf of Mexico is topped by cold, dry air aloft and a powerful jet stream pivoting out of the West. This provides the instability needed to generate thunderstorms.

In these cases, wind shear — the change in wind speed and direction with height — is intense. This allows supercells to form and provides the spin needed to stretch and tilt into tornadoes.

Violent tornadoes are much less common from midsummer through fall and winter, but they can happen any time of year if the volatile setup is in place. They have occurred in every month, including winter.

For example, Christmas Eve F4 tornadoes tore through parts of Arkansas and Missouri in 1982 and Tennessee in 1988.

Top tornado states: It should come as no surprise where violent tornadoes occur most often.

From 1950 through 2023, the conventional Plains "Tornado Alley" states of Oklahoma, Texas, Iowa and Kansas had the largest number of violent tornadoes.

Elevated violent tornado counts also extend eastward into the Ohio Valley and a southern corridor that includes Alabama, Mississippi and Tennessee.

Damage from at least one violent tornado has been observed in 33 of 50 states.

Violent tornadoes are less common east of the Appalachians but have occurred as far north as Massachusetts and upstate New York and as far south as Florida.

Just one violent tornado has been documented from the Rockies to the West Coast.

On July 21, 1987, an F4 tornado reportedly uprooted 1 million trees as it ripped a path across the Teton and Yellowstone areas of northwestern Wyoming. The tornado affected elevations between 8,500 and 10,000 feet, making it the highest altitude that a violent tornado has been documented.

M​ORE ON WEATHER.COM

-​ How Often Your State Sees Tornadoes In A Year

-​ 15 Severe Safety Tips That Could Save Your Life

-​ How Tornadoes Are Rated

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. His lifelong love of meteorology began with a close encounter with a tornado as a child in Wisconsin. He completed a Bachelor's degree in physics at the University of Wisconsin-Madison, then a Master's degree working with dual-polarization radar and lightning data at Colorado State University. Extreme and bizarre weather are his favorite topics. Reach out to him on X (formerly Twitter), Threads, Facebook and Bluesky.