2024 had some wild weather. Here’s why.

If it feels like the weather was a bit much this year, you’re not imagining things. The United States dealt with “hyperactive” hurricane and tornado seasons, and a burgeoning La Nina is in large part to blame.

The term “hyperactive” may seem hyperbolic, but it’s actually a meteorologically defined threshold. And while tornadoes and hurricanes are vastly different phenomena, they have one thing in common: a developing La Nina weather pattern that helped increase the frequency of tornadoes and hurricanes in 2024 — even as the pattern hasn’t materialized exactly how scientists expected.

For a hurricane season to be hyperactive, it has to churn through 159.6 units of “accumulated cyclone energy” — a metric that gauges how much energy a season’s storms churn through. That’s about 65% more than the 1991-2020 median.

The 2024 Atlantic hurricane season, which produced 18 named storms, expended 161.6 units. Five hurricanes struck the Lower 48 — Beryl, Debby, Francine, Helene and Milton. Three slammed Florida.

For tornadoes, records are a lot shakier. Data technically goes back to 1950, but most tornadoes back then were missed or not reported. It wasn’t until about 1990 that cataloging tornadoes became routine and reliable, and only in the past decade have cellphones provided documentation of events that otherwise would have been overlooked.

Still, January through November featured 1,762 preliminary tornado reports. That falls just shy of the top spot. In 2004, 1,787 tornadoes were tallied by the start of December.

The 1991-to-2020 average during this same time frame is 1,187 tornadoes nationwide — putting this year just over 48% ahead of average.

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How La Niña conditions can make their mark

La Nina is the opposite of El Niño, both phases of an alternating weather pattern that begins in the tropical Pacific. In the case of La Nina, cooler than average water temperatures prevail in the eastern Pacific. That cooling chills the air above, causing it to sink and driving pressure higher, which in turn affects weather features in the atmosphere and triggers downstream effects in North America and beyond.

A clear link exists between La Nina and hurricanes. The sinking air in the Pacific is counteracted by rising air in the Atlantic. (After all, if the air is sinking in one place, it needs to be rising in another.) That upward motion makes it easier for hurricanes to form.

When the winds are too strong, fledgling storms can be torn apart before they ever become hurricanes. That’s usually not an issue during La Nina years. The ongoing conditions have also allowed hurricanes to survive longer, which in some cases meant they could drift far enough west to affect the United States.

With tornadoes, the relationship is more nuanced. There is research to suggest that the Great Plains sees at least some uptick in tornadoes during La Nina years because the climate pattern shifts the position of the jet stream, or a river of winds in the upper atmosphere. The wavier jet stream favors the formation of low pressure systems in the Rockies, which draw warm, humid air north across the Plains and set the stage for rotating thunderstorms.

One catch is that this year, La Nina conditions did not begin to emerge until the autumn. For tornado season, the pendulum was swinging through the “neutral” category from El Niño to La Nina.

But there’s emerging research to show that quick swings between El Niño and La Nina, which happened between March and May, can result in booming, busting tornado barrages across the Corn Belt and Nebraska in particular, with enhancement elsewhere on the Plains.

Iowa and Nebraska in particular this year saw repeated onslaughts of destructive tornadoes, and the entirety of the U.S. Great Plains, often dubbed “conventional Tornado Alley,” roared to life in a way it hadn’t for years.

And there’s no telling what next year’s weather conditions might bring.

At first glance, if La Nina conditions weaken in the spring and shift back again toward El Niño, it could lead to near average or slightly below average hurricane activity — though any decrease in atmospheric favorability might be offset by anomalously warm ocean waters.

For tornado season in the spring, the Deep South may see a bit extra activity in February or March under these same conditions, with increased tornado activity in Kansas and Oklahoma in April. For May, a near or slightly above normal stretch of tornado activity is probable.