No Killer Tornadoes in May

May is typically the busiest month for twisters in the lower 48. This year, not one that spun up during the month proved fatal. For the first time in seven years, the United States had no killer tornadoes in May, a welcome statistic for parts of tornado country accustomed to holding their breath during the springtime. While numerous tornadoes did form through the Plains, in the swath traditionally known as Tornado Alley, the vast majority of strong tornadoes avoided communities and structures. The fortuitous distribution of storms, coupled with advanced forecasts and warnings, are credited for the lack of serious casualties. ¹

EF5 tornadoes are the most powerful storms on the Enhanced Fujita Scale

EF5 tornadoes are the most powerful storms on the Enhanced Fujita Scale, which allows weather officials to use damage indicators to make a judgment of a tornadoes' likely wind speeds. EF5 tornadoes have maximum wind speeds of more than 200 miles per hour and can cause 'complete destruction.' Eight years ago, the Newcastle-Moore, Oklahoma 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. ² 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 make up a tiny fraction of all tornadoes. That's a good thing, given their winds of 200 mph or greater. 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. The current pause happens to coincide with a general reduction in EF-4 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. ²

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The lack of violent tornadoes

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. 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. ² This year has been a quiet one for severe storms in general. Said AccuWeather Senior Weather Editor, Jesse Ferrell,“So far 2021 has seen the second fewest issuances of severe thunderstorm and tornado warnings since 1995, when radar data became routinely available. When it comes to tornado reports, 2021 is currently in the bottom 25th percentile, meaning this year has seen fewer tornado reports than 75% of the year since 1950.” ³ Mother Nature can be extreme, variable and fickle. Events and years unlike recent experience are inevitable. When unexpected (or inconceivable) weather events occur, we should try to figure out what happened and why, instead of lazily attributing it to man-made global warming. ⁴

References

Matthew Cappucci, “The US avoided tornado fatalities in May,” washingtonpost.com, June 6, 2021

Ian Livingston, “For a record 8 years, the US has avoided the most destructive kind of tornado,” washingtonpost.com, May 22, 2021

Zachary Rosenthal, “May snaps long standing streak for strong tornadoes in US,” accuweather.com, June 11, 2021

Dan Sutter, “The 'new normal' that wasn't,” wattsupwiththat.com, May 23, 2021