A Tiny Fraction of Tornadoes Claim the Most Lives. Saturday's Violent EF4 Iowa Tornado Was the Latest Example.

A National Weather Service damage survey team rated a tornado that raked through parts of Madison, Warren, Polk and Jasper counties Saturday an EF4 tornado with estimated peak winds of 170 mph.

Six people were killed in Madison County.

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 are 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.)

"It was just complete devastation," Stacie Carter told weather.com's Jan Wesner Childs in a phone interview, describing her home in Madison County after the storm passed Saturday. "Roof down. Windows blown out. Garage was gone to the foundation. It was just total devastation. It just looked like everything had been shredded through a woodchipper."

From 2000 to 2019, the most recent year in which finalized tornado counts are available from NOAA's Storm Prediction Center, violent tornadoes were responsible for roughly half of all U.S. tornado deaths.

But these tornadoes are, thankfully, relatively rare. In that same 20-year period, violent tornadoes made up less than 0.5% of the nation's tornadoes.

The death toll from these 113 violent tornadoes (741 lives) exceeded the death toll from the other 24,442 tornadoes combined (727 lives). Put another way, each F/EF4 tornado killed an average of four people, while F/EF5 tornadoes killed an average of 37.

Almost 90% of tornadoes from 2000 to 2019 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.

Since 1950, the U.S. has averaged nine violent tornadoes per year, according to NOAA.

There were three violent tornadoes in 2021 – Newnan, Georgia, on March 25; and a pair of long-track tornadoes from Arkansas into southeast Missouri, northwest Tennessee, and Kentucky, including Mayfield, on Dec. 10 – all rated EF4. The Mayfield tornado claimed 57 lives, according to the National Weather Service.

Four of the six violent tornadoes in 2020 happened within a week's time from Easter Sunday to the following Sunday. Three of those occurred within 40 miles of each other in southern Mississippi.

Since 2020, nine of the last 10 violent tornadoes in the U.S. claimed at least one life.

But some years have few, if any, violent tornadoes.

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

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

Spring Is Peak Time of Year

We found a broad peak from April through early June, during which 61% of violent tornadoes occurred.

Multiple violent tornadoes can often cluster in higher-end outbreaks, accounting for some of this spring peak. Among these historic outbreaks include:

• 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.

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.

The Top Violent Tornado States

It should come as no surprise where violent tornadoes occur most often.

From 1950 through March 2022, the conventional Plains "Tornado Alley" states of Oklahoma, Texas, Iowa and Kansas had the biggest number of violent tornadoes.

Saturday was Iowa's first EF4 tornado since Oct. 4, 2013, according to the National Weather Service in Des Moines. It's 69.5-mile long path was also the state's second longest in records dating to 1980.

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.

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