Tornadoes that hit the top of the intensity scale: What are the odds?

Tornadoes rated a 5 on the National Weather Service’s intensity scale are so strong they can level strong frame houses, debark trees, launch cars great distances through the air and etch a scar into the earth. More than a decade has elapsed since the last one.

A recordlong streak of 3,654 days since the last tornado rated a 5 is ongoing, and it’s the longest by more than two years.

While it might be comforting to think that something has changed to tame these monstrous twisters, such a view would be misplaced. The lack of these top-tier tornadoes probably has more to do with luck and storm rating nuances than science.

They still pose a threat.

The last tornado rated an EF5 on the 0 to 5 Enhanced Fujita scale for tornado strength formed in central Oklahoma on May 20, 2013. Along its devastating path from Newcastle to Moore, just south of Oklahoma City, 24 people died, 212 were injured, and as many as 1,200 homes and dozens of businesses were destroyed, including two elementary schools.

Tornadoes this strong – with peak winds of at least 200 mph – are rare, making up less than a tenth of a percent of all twisters. Still, on average, they’ve occurred about every other year; 59 have struck since 1950. They’ve caused 1,347 deaths, or an average of 23 per tornado.

Some years have seen multiple tornadoes rated a 5, and several notorious days have featured multiple 5s. In 1953, tornadoes this strong occurred on five different days. In 2011, they occurred on three different days. The most 5s in one year is seven – all of which struck within 24 hours during the 1974 Super Outbreak.

The system used to rate tornadoes has changed over time, complicating any efforts to interpret trends. Two decades ago, the original Fujita (F) Scale – named after tornado scientist Theodore Fujita – was modified to become the Enhanced Fujita scale

“The original F scale had limitations, such as a lack of damage indicators, no account for construction quality and variability, and no definitive correlation between damage and wind speed,” a National Weather Service website about the scales says. “These limitations may have led to some tornadoes being rated in an inconsistent manner and, in some cases, an overestimate of tornado wind speeds.”

Tim Marshall, a meteorologist and engineer who is part of the Weather Service’s Quick Response Team for surveying tornado damage, said he does not believe tornadoes have become any less violent.

If anything, “weather has become more violent as more people get in its way,” Marshall said in an interview.

Pure chance plays a role as to whether a tornado can earn a rating of 5. The full furies of its winds must hit a well-built structure. If a violent tornado with winds equivalent to a 5 only passes over forest or farmland, it cannot earn that rating.

In other words, it’s probable EF5 tornadoes have occurred in the last decade, but just haven’t hit a strong building where their force could be evaluated. A 2021 study found the Weather Service is substantially underestimating the strength of some rural tornadoes.

Marshall said a refresh to the EF-scale is in the works that will incorporate more indicators for evaluating damage, including more focus on rural locations, all of which should refine any perceived shortcomings.

Even when a tornado earns a rating of 5, it is typically only for damage observed over a tiny sliver of its track. When tornado damage is surveyed, a rating is assigned along many damage indicator points along the storm’s path.

Marshall, who says he has surveyed at least eight 5s during his career, was an author on a study following the 2013 Moore tornado which described the rating process and compared it to other top-tier tornadoes.

An EF5 rating requires that a “ ‘well constructed’ home is swept clean from its foundation,” according to the study.

Only 0.4 percent of Moore’s damage indicators reached EF5 level, while about 1% reached that mark in three other infamous EF5 tornadoes. By comparison, EF4 damage was much more common in these twisters – observed at about 20% of the areas surveyed.

For the 2013 Moore tornado, points along more than 4 miles of the track exhibited EF4 damage, at least half of it continuous. A few isolated spots exhibited EF5 damage within that 4-mile swath.

Tornadoes don’t need to be rated a 5 to be disastrous. 2023 opened with one of the highest tornado-related death tolls in modern history, including 17 fatalities from the EF4 tornado that struck Rolling Fork, Mississippi, in late March.

Three twisters since 2019 have killed 19 people or more. 2021, for example, produced the deadliest December on record for twisters, primarily driven by the Mayfield, Kentucky, tornado. It killed 57 people as it remained on the ground for three hours, devastating numerous communities.

“There’s no difference between a high-end EF4 and an EF5. Both are deadly, and both must be taken seriously,” said Marshall.

Marshall was on one of three teams to survey the Mayfield EF4 and it was “the closest to EF5 that I can remember” since the Moore EF5 of 2013, he said.

But as the surveying teams could not find EF5 damage consistent with winds of at least 200 mph, the tornado was ultimately ranked just shy of that mark, with 190 mph winds.

Some buildings where the storm’s most violent winds struck were completely obliterated, but they were so poorly constructed it was impossible to know if EF5 winds affected them. “They were horribly constructed and could not resist 100 or even 150 mph wind let alone 200 mph,” Marshall said.

The recent lack of EF5 tornadoes brings to mind to the “major hurricane” landfall drought that ended several years ago. After Hurricane Wilma struck southwest Florida in 2005, there wasn’t a single hurricane rated Category 3 or higher to strike U.S. shores for nearly 12 years (Sandy, which struck New Jersey in 2012, wasn’t officially considered a hurricane at landfall). The drought came to a sudden and dramatic end in 2017 with Category 4 Hurricane Harvey, and then a slew of others.

It’s “just a matter of time” before another EF5, Marshall said. “That day is coming.”

The Washington Post’s Jason Samenow contributed to this report.