Ag Weather Forum

On the afternoon of July 15, 2024, a severe windstorm developed in eastern Iowa that moved through northern Illinois, southern Wisconsin, and northern Indiana into the early morning hours of July 16. The windstorm was classified as a derecho, or a windstorm that contains constant severe wind gusts along its path of at least 240 miles. Some of these wind gusts need to be hurricane strength -- more than 74 miles per hour, which did occur.

More information about the details of this derecho can be found here: https://www.dtnpf.com/….

The term derecho has gotten a lot of attention in recent years due to the prevalence of social media, but also because of a significant one that struck during the late summer of 2020. Since then, the term derecho has been met with perked ears and standing hairs for those that witnessed, read, or saw damage from that windstorm.

Multiple derechos have formed since the infamous storm that rolled through on Aug. 10-11, 2020, but none of them have had nearly the impact of that late-summer storm. But the one that moved through a week ago was the closest we've seen, coming through the same areas as the one from four years ago. This year's derecho will not be remembered as vividly as the 2020 storm, mostly due to the more limited damage. But why did this year's storm not have the same impact as the one four years ago?

DAMAGE NOT NEARLY THE SAME AS 2020

The windstorm that moved through eastern Iowa, northern Illinois, and northern Indiana in July 2024 followed a remarkably similar storm track to the one that moved through in August 2020. But the damage was not nearly the same.

Multiple stories were written about the impact from that storm in 2020, which at the time was the costliest thunderstorm complex in the nation's history.

In 2021, we marked the one-year anniversary of the derecho: https://www.dtnpf.com/… and https://www.dtnpf.com/….

You can see a lot more coverage DTN did about the derecho -- including its impact on crops, grain storage and even grain prices in 2020 -- at the bottom of this article.

The storm from this year was not nearly as costly. Though it formed in roughly the same areas and went through the same corn and soybean fields as the one in 2020, several factors came together to make this year's derecho a far cry from the one from four years ago.

DIFFERENT BEGINNINGS, TIMING

The differences between the two derechos start with their beginnings. The one from 2020 started as a cluster of thunderstorms the night before in southeast South Dakota and northeast Nebraska. In going across Iowa during the morning, the storm strengthened as it moved eastward across the state during the afternoon, then matured going through Illinois in the late afternoon and evening. The immediate presence of a cluster of thunderstorms already built the potential for more sustained and widespread damage and the strength during the afternoon allowed for more potential to use the heat of the day to ride through the Corn Belt.

This year's derecho started differently. Instead of continuing thunderstorms from the previous night, there were clusters of thunderstorms developing over central Iowa in the afternoon that formed together to get a derecho going more in the late afternoon and evening hours. Damage was then spread out through these different segments of the storm. Instead of one unified storm like the 2020 derecho, this one was slightly more segregated in the damage reports that formed. While a unified presentation was noted on radar, the 2024 storm lacked a singular, unified "rear-inflow jet", or a rush of wind coming from behind the leading edge that pushes the windstorm forward.

THE DIFFERENCE IN CONSTRUCTION, WIND DAMAGE

Since it was one large zone instead of several along the storm length, the rear-inflow jet from 2020 produced incredibly strong winds over 100 mph and a peak wind gust of 130 mph, a comparison to a major hurricane. Wind gusts over 80 mph were widespread and common and the damage was severe.

In 2024, the rear-flow jets were more localized in at least two sections of the storm, which led to wind gusts more commonly in the 70-80 mph range with only two recorded gusts over 100 mph. The 2020 storm had 12 recorded gusts over 100 mph.

The more localized nature of the storms may also explain the increased tornadoes from the 2024 storm, in which there were 41 confirmed tornadoes compared to the 2020 storm which contained 24.

Though the two derechos formed in similar fashion under similar conditions, their differences in development and timing led to major differences in the damage. While the damage was severe across both storms, the increased winds of the 2020 storm led to much more widespread damage. Buildings were destroyed and debris was scattered miles away from their original locations.

THE DIFFERENCE A MONTH MAKES

The time of year also played a role, especially for agriculture. The 2020 derecho occurred in August, a time when corn was filling its grain and some of the crop was nearing maturity.

The USDA NASS weekly Crop Progress report from the Sunday prior indicated that nearly all of the corn crop had completed silking in Iowa, Illinois and Indiana and most of the crop was past its dough stage (66%, 66% and 56%, respectively). Even some of the corn had dented (9%, 10% and 4%, respectively).

This year's corn is not nearly as far along, as should be expected. This year, corn had not finished silking (44% Iowa, 62% Illinois, and 42% Indiana) and very little of the crop had reached the dough stage (6%, 8% and 3%, respectively). None of the crop has reached the dented stage, either.

The weather situation in 2020 was also more severe, as much of Iowa was undergoing a flash drought with conditions worsening after the derecho across all three primary states. This year, none of the area that was hit is under drought and rainfall in the weeks prior had given rise to good soil moisture, allowing the crop to be more resilient to the strong winds.

In other words, this year's crop, though it may have sustained some damage, has a greater ability to right itself before harvest given good weather conditions to follow.

There can still be some weather challenges ahead for this year's crop, though. The setup for severe weather increases heading into August as does the heat, which will come at a critical time period for the filling corn crop. This year's crop may have dodged a collective bullet, but is not out of the woods yet.

To find more weather conditions and your local forecast from DTN, head over to https://www.dtnpf.com/…

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DTN stories about the 2020 derecho, its impact and tips to prepare for future derecho or deal with their aftermath:

-- "Straight-Line Winds Picked Up Speed Across Iowa, Illinois," https://www.dtnpf.com/…

-- "Storm Devastates Commercial, On-Farm Grain Storage Just Weeks Ahead of Harvest," https://www.dtnpf.com/…

-- "Crop Experts Find Wide Variety of Damage to Corn, Soybeans Across State," https://www.dtnpf.com/…

-- Editors' Notebook, "The Answer, My Friend ..." https://www.dtnpf.com/…

-- "Estimated 6.95 Million Illinois Corn Acres Were in Path of Destructive Storm," https://www.dtnpf.com/…

-- Todd's Take, "Corn Finds a Bullish Trigger," https://www.dtnpf.com/…

-- "USDA Estimates 14 Million Acres of Insured Crops in Iowa Path of Storm," https://www.dtnpf.com/…

-- "Mangled Grain Storage Adds to Harvest Uncertainty," https://www.dtnpf.com/…

-- "Foreign Matter Takes on New Meaning After Midwest Storm," https://www.dtnpf.com/…

-- "Grain Bins Can Be Built to Sustain Hurricane-Force Winds, But at a Cost," https://www.dtnpf.com/…

-- Kub's Den, "Effects of August Derecho on Iowa Corn Basis Still Linger," https://www.dtnpf.com/…

-- "Tips to Manage Corn Residue in Derecho-Damaged Fields," https://www.dtnpf.com/…

-- "Grain Bin, Building Companies Hasten to Mend Derecho Damage," https://www.dtnpf.com/…

-- "With Recovery Comes Preparedness for Iowa Farm Family," https://www.dtnpf.com/…

-- "One Year Later: A Look at 2020's Destructive Derecho," https://www.dtnpf.com/…

-- Editors' Notebook, " 2020 Derecho Showed Midwest Resilience," https://www.dtnpf.com/…

-- "Congress Adds $10 Billion in Disaster Aid for Hurricanes, Wildfires, Derechos, Other Storms," https://www.dtnpf.com/…

-- "New UNL Research Aims to Strengthen Grain Bins Against Natural Disasters Such as Derechos," https://www.dtnpf.com/…

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John Baranick can be reached at john.baranick@dtn.com

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