Swarms of tornadoes have been tearing across the United States for nearly a month straight, keeping meteorologists and the public on guard for weeks. It’s been the most active May for severe weather since 2011 and has featured violent tornadoes, a 100 mph downburst that tore through Houston and even hail larger than grapefruits.
End of carouselTornadoes touched down on all but two days between April 25 and May 27 — that’s 94 percent of days. That beats out other exceptionally active stretches in recent memory — such as in 2017, 2019 and 2022 — when between 88 percent and 91 percent of days had tornadoes.
Eight days during the recent spate netted 40 or more reported tornadoes, with more than 100 filtered tornado reports on April 26. At least three dozen people have been killed by tornadoes in 2024, including 23 since May 1.
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The extreme season is the result of a stagnant weather pattern that has sent a barrage of disturbances barreling across the central states. Each has whipped up a slew of rotating thunderstorms or supercells, cranking out tornadoes from the High Plains to the East Coast.
Now, after a trying month meteorologically, a large-scale pattern change could spell a drop-off in tornado activity into next week.
How many tornadoes have there been so far this year? And what is normal?
May is typically the most active month of the year for tornadoes in the Lower 48. That’s because of a seasonal clash of air masses. As summer’s warmth tries to build northward — and bring along Gulf of Mexico humidity — it encounters lingering pockets of winter’s chill that surge southeast out of Canada. The colliding air masses brew strong to severe thunderstorms, and strong winds aloft in the jet stream sculpt them into spinning supercells.
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By late spring, the highest concentration of tornadoes usually shifts from the Deep South to the southern Plains. That creates a bull’s eye over Texas, Oklahoma and Kansas. A lesser, albeit considerable, risk also stretches westward to the edge of the Rockies, northward toward the southern Great Lakes, then east through most of the Mid-Atlantic, Midwest and South.
For the most part, this month’s storminess has hit in typically prone areas. That said, northern zones like Nebraska, Iowa and parts of the Ohio Valley have seen an unusually high tornado count for this early in the season.
Why have there been so many tornadoes this year?
Across the Deep South, namely Mississippi and Alabama, the spring tornado season was unusually quiet. The National Weather Service in Birmingham, for example, has issued only four tornado warnings this year — the fewest for this date since at least 1987. By this time last year, it had issued 44, and 175 through this date in 2011. The Jackson, Miss., office has issued just 19 tornado warnings, its fewest since 1986.
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That’s typical of an El Niño winter, when the jet stream — a river of swiftly moving winds in the upper atmosphere — dives farther south over North America. That allows cooler air to spill all the way down to the Gulf Coast, shunting any severe weather risk into the Gulf of Mexico or Florida.
But in the late spring, the El Niño climate pattern wore off quickly, making way for a burgeoning La Niña. That sudden transition is rare, but historically it has been associated with above-average tornado activity over the Plains.
We’ve also had a favorable jet stream pattern. That jet stream has dipped in the west, producing a “trough” of low pressure. And the trough has been spitting out smaller “shortwave” disturbances seemingly nonstop to trigger storms.
The same jet stream has also been surging over the Gulf Coast states, allowing warmth and moisture to waft northward. That makes for a reservoir of storm fuel.
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Each storm system has either used up or scoured out most of the available storm fuel over the Plains, but persistent “return flow,” or southerly flow in the wake of storm systems, has helped the atmosphere to reload gulf moisture time and time again. That has meant back-to-back tornado outbreaks can occur on consecutive days — like on April 26, when 108 reported tornadoes occurred across Nebraska and Iowa, followed by 51 preliminary tornadoes on the evening of April 27. Among them was an EF4 in Marietta, Okla., on the 0-to-5 Enhanced Fujita intensity scale, and multiple EF3s that claimed lives in Sulphur and Holdenville, Okla.
When those factors are added together, it’s no surprise the tornado season has been hyperactive. As far as textbook tornado setups go, this month has had a lot of them.
Is it unusual to have so many deadly twisters?
The stretch from April 26 to May 26 has been the deadliest such window since 2014, when 34 people died because of tornadoes. Otherwise, the past eight years (from 2015 to 2023) had 30 deaths total during the same time frame.
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The 23 tornado deaths in May is also the most in the month since 2013, when 32 people died. That month featured the most recent confirmed EF5 tornado that struck Moore, Okla., on May 20, as well as the El Reno, Okla., tornado that killed renowned storm chaser Tim Samaras.
Though no individual tornadoes this year have resulted in a double-digit death toll, the sheer number of tornadoes that caused one or more deaths is notable. At least 14 killer tornadoes occurred between April 26 and May 26. That’s the third most on record for that time frame dating back to 1950.
When will it finally end?
Historically speaking, June is the second most active month for tornadoes in the United States. That’s around the time the greatest concentration of tornadoes shifts from Texas, Oklahoma and Kansas to Colorado, Nebraska and the Dakotas, particularly the High Plains.
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There’s no reason to think that severe weather chances are going to suddenly flatline, but we do think that, at least briefly, the Plains should catch a breather. High pressure will become established in the western United States, with a bowling ball upper-level low in the east. That should induce northwesterly flow over the Plains, bringing cooler, drier air to the nation’s heartland and suppressing the warmth and moisture needed to get big storms. There will also be a dearth of large-scale “triggers.”
Still, smaller-scale setups can and will happen. And it’s likely that sprawling storm complexes called MCSs, or mesoscale convective systems, will occur nightly with strong winds and lots of lightning. But, at least temporarily, the chances of another tornado outbreak are limited.
More severe weather stats
In case it’s still not clear just how wild of a stretch this past month has been, here’s a recap by the numbers:
More than 1,250 tornado warnings were issued during the month-long stretch, in addition to more than 5,600 severe-thunderstorm warnings.
If all the warnings were placed side by side perfectly across the country, they would cover more than 100 percent of the land area. Oklahoma has had enough warnings to be covered seven times over, Iowa six times over, and Missouri five times over. Nearly 48 percent of both Oklahoma and Iowa has been placed under a tornado warning and instructed to shelter at least once this season. In Kansas, 99.5 percent of land has been encompassed in one or more severe thunderstorm warnings.
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The National Weather Service in Norman, Okla., has been working to issue said warnings seemingly nonstop. It has drawn up more than 600 of them, including 133 tornado warnings. Dallas, Tulsa, Springfield, Mo., and Omaha are next in line to have issued the most warnings of any of the nation’s 122 Weather Service offices.
Between April 27 and May 26, five days have had PDS tornado watches issued, meaning it was a particularly dangerous situation. Those are bulletins cautioning residents that especially intense tornadoes might form and that they should have multiple ways to be notified of tornado warnings.
Between April 25 and May 27, 17 days had PDS tornado warnings, the most on record for that stretch. A whopping 104 of them were issued. PDS tornado warnings, which were nationally implemented in 2016, are usually reserved for when a significant tornado is sighted visually or detected on radar.
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Most sobering were the 14 tornado emergencies issued — a souped-up tornado warning only utilized during the most extreme tornado events. They are used to warn of an immediate life-or-death situation associated with a confirmed large, strong to violent and extremely dangerous tornado. Emergencies were issued in Nebraska, Iowa, Oklahoma, Michigan, Alabama, Tennessee, Texas and Kentucky on seven days. Michigan’s was the first on record for the state.
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