The year 2024 was scaring people across large parts of the US as hurricane warnings and phone calls sent them scrambling for cover.
More than 1,100 storms have been recorded through May – a first but nearly double the 30-year average for that period and behind only 2011, when deadly hurricanes lashed the US Southeast.
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The US experienced several major disasters in 2024. Hurricanes destroyed homes from Texas to Minnesota and east to West Virginia and Georgia. They caused extensive damage to several towns, including Greenfield, Iowa; Westmoreland, Kansas; and Bartlesville, Oklahoma. Barnsdall, Oklahoma, was hit twice in two months.
In May, at least every day there was a hurricane somewhere in the country.
Greenfield, Iowa, after an EF4 tornado ripped through the town on May 21, 2024, amid a deadly storm surge.
What makes some years so stormy? I am a meteorologist who studies hurricanes and thunderstorms. Here is what created the perfect conditions for these violent storms.
2 essential storms, on steroids
The period of extreme activity is due to the abundance of two important tools for storms: shear and instability.
The jet stream – a group of strong high-level winds that usually blow west to east, flowing between warm air to the south and cooler air to the north – plays an important role in how and where the weather systems change, and the wind shear.
In April and May 2024, the jet stream tended to descend south over the western US before returning to the northeast across the Great Plains. This is a perfect way to produce severe storms in the central US
The area has long been considered Tornado Alley and some of the influences that can cause tornado weather. The red curved line shows the warm front east of the jet stream. Image provided by NOAA
In the area east of the southern jet stream, the air rises. That creates a strong low pressure system, which causes the winds near the ground to blow from a different direction than the one going up, which causes the wind to not blow.
To make this year even more active, persistent heat waves were common in Mexico and Texas, while the Rockies and the far north of the United States remained cool. The extreme temperature difference created a stronger than normal jet stream, leading to drastic changes in wind speed and altitude. As a result, air shaving has been used on steroids.
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A change in wind speed with height can cause the wind to have a rotational motion. The rapidly ascending air of a thunderstorm can tilt the motion to form a rotating thunderstorm that can lead to the rotation of the storm.
The Gulf of Mexico was also much warmer than usual, producing more heat and moisture that could be carried north to fuel thunderstorms. That creates atmospheric instability, which is another important ingredient for storms.
Image provided by the National Weather Service
The weakening of El Nino was a warning
This perfect combination of hurricane ingredients was not entirely surprising.
El Nino and La Nina – opposing weather patterns in the middle of the Pacific Ocean – can affect winds and weather around the world. A 2016 study found that when El Nino transitions to La Nina, the number of hurricanes in the Central Plains and Upper Midwest is often larger than usual.
READ MORE: La Nina is on the way back. Astronomer explains what to expect
That’s exactly what happened in the spring of 2024. Tornadoes have mostly been in the traditional Tornado Alley, from north Texas to South Dakota, extending through the Corn Belt through Iowa and into reach east to Ohio, consistent with the study’s findings.
How El Nino and La Nina influence hurricane behavior.
How does storm activity change?
However, the active season on the Great Plains was somewhat unusual. The findings show a long-term trend of a decrease in hurricane numbers in the region and an increase in hurricanes to the east, near or east of the Mississippi River.
That change is consistent with what climate models suggest is likely to occur during the remainder of this century as global temperatures continue to rise.
A map showing the average number of days per year where a tornado registers EF1 strength or greater within 25 miles of each location shows Tornado Alley moving eastward. Period covered 1986 to 2015. Image provided by NOAA Storm Prediction Center
The expected decrease in the number of hurricanes in the Plains is likely related to increased temperatures in the high desert of the Southwest and Mexico. That heat flows over the Great Plains a few thousand feet above the earth, and forms a blanket or mantle. The cover allows heat and moisture to accumulate until it breaks through to form a thunderstorm. This hot, humid air is why the central US is home to some of the strongest hurricanes on Earth.
Another theory is that, with climate change, it may be harder to break through that blanket, reducing the number of hurricanes in the Plains. At the same time, increasing heat and humidity in some areas will cause more storms in the East.
Long-term patterns and weather forecasts also suggest more storms during the colder months, especially in the Southeast. Hurricanes also occur on a few days each year, but on the days they do occur, there are likely to be more storm surges.
This article is reprinted from The Conversation under a Creative Commons license. Read the first article.
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