Eight years ago, the Newcastle-Moore, Okla., tornado, rated EF5, mercilessly scoured the earth along a mile-wide swath through the heart of several neighborhoods. In its wake, 24 were dead, including seven children at Plaza Towers Elementary. It would be years before the scars were hidden, but the pain remains fresh.
Since then, there have been no twisters rated 5 on the Enhanced Fujita scale for tornado damage. The most dangerous and destructive of their kind, EF5s (or F5s before 2007) make up a tiny fraction of all tornadoes. That’s a good thing, given their winds of 200 mph or greater.
At 2,924 days since the Newcastle-Moore EF5, the ongoing streak has set a record, and we’ll probably extend it further. The question, however, is how far.
The recent lack of EF5s fits into a trend toward fewer of these most intense tornadoes in recent years. However, because of their rarity and some changes in the way tornadoes are rated, experts aren’t convinced of how meaningful this trend is.
To begin, it’s difficult to draw inferences from events that happen infrequently. There have been 59 F/EF5 tornadoes in the modern record, which began in 1950. An annual average of EF5 tornadoes yields just shy of one per year. But violent tornadoes can come in swarms. In the years when you have one, there is a decent chance that there’s more than one. For instance, 2011 had six across three days in April and May.
In addition, the EF scale has limitations, because tornadoes are rated on what they hit, not what they miss. In other words, if a violent tornado plows an open field, it wouldn’t earn the same high rating that it would if it a leveled a town. Ratings on today’s EF scale for tornadoes are based on 28 potential damage indicators, which range from small buildings to large buildings, and include other assorted objects.
Long pauses in these mammoth twisters are not uncommon because of their infrequency. Over the past seven decades, there have been seven lengthy streaks of 1,000 days or more without tornadoes of EF5 intensity.
Before the current streak, the longest previous gap between EF5s or F5s spanned May 3, 1999, when a devastating tornado yet again struck Moore, Okla., and May 4, 2007, when a massive twister demolished Greensburg, Kan.
While so-called droughts in these top-tier tornadoes are not uncommon, the current pause does happen to coincide with a general reduction in EF4-plus twisters more broadly, or what the meteorological literature refers to collectively as “violent” tornadoes.
There have only been 11 violent tornadoes recorded in the past four years. During the April 27, 2011, Super Outbreak, that many occurred in a single day.
In 2018, not a single violent tornado touched down for the first time on record. So far in 2021, just one has been observed.
The lack of violent tornadoes both this year and in 2018 is all the more remarkable, considering increasing development, which gives twisters more stuff to hit.
The EF-5 drought is better phrased as "a drought of tornadoes causing EF-5 damage" and I think that is even more worth celebrating. Many of the markers for that level of damage require construction typically found in more populated areas.— Dylan Lusk (@wxdylanl) May 20, 2021
Even so, Harold Brooks, senior research scientist with the NOAA National Severe Storms Laboratory, urged caution in analyzing violent tornado trends. He told The Washington Post that “the most reliable” accounting of tornadoes includes all twisters rated EF1 or higher. “Counts of events stronger than that have been affected by changes in reporting over the years,” he wrote.
In the past, he said, it was arguably easier for a tornado to earn a high rating. “Pre-1978 tornadoes were rated retrospectively by summer students based on the text description of the damage,” he wrote.
In addition, when the F scale changed to the EF scale in 2007, Brooks said, changes were made “in what is needed to get the highest rating,” which makes comparisons over time difficult.
Changes in the sturdiness and the engineering of buildings may also have affected how ratings have evolved.
“It is incredibly difficult to consider ALL possible construction outcomes,” Stephanie Pilkington, an assistant professor of engineering at the University of North Carolina at Charlotte, wrote to The Post. “Building standards have improved greatly since the 90s with concern for wind.”
Could the weather itself have changed to result in fewer of these intense tornadoes? It’s hard to make a compelling case for that.
The documented eastward shift in tornado activity in recent years from the Plains toward the South, if anything, would put twisters into higher population regions overall. And even though we haven’t seen an EF5 enter the books in recent years, we’ve had plenty of active tornado seasons, including May 2019, with more than 500 tornadoes.
Perhaps we shouldn’t tempt fate in dissecting the EF5 tornado drought. There’s still plenty of time this year for tornadoes to flare up, although weather patterns do not appear favorable in the near term. Historically, two-thirds of all F/EF5s have occurred in April or May, and odds thankfully dwindle significantly once past June.