July 2024 may be history, but it’s worth a look back at unusual weather events and trends that developed in the Midwest. Illinois was in the heart of most of these events, although they spilled over into Iowa, Indiana, Missouri and Minnesota.

For starters, the remnants of Hurricane Beryl moved up through the Midwest, bringing much-needed rain to many areas, including east-central Illinois. In some places, 3 or more inches fell, and less in other locations.

Then a major thunderstorm event brought up to 8 inches to Fulton County, Ill., and lesser amounts to surrounding areas. While many soils there are on the sandy side, soils in surrounding counties are not.

Water was allowed to overtop the dam near Nashville, Ill., to avoid risking breaking the dam and creating even more severe flooding.

FILL THE GAUGE: Over 6 inches of rain fell in one night near Marietta, Ill., with even higher totals elsewhere.

“We also had a derecho event with strong, straight-line winds in some locations,” says Trent Ford, Illinois state climatologist with the Illinois Water Survey at the University of Illinois. “It created a lot of damage, but it was not nearly as severe as the derecho which came through here after devastating Iowa in August 2020. That was a much stronger, broader storm system.”

Why these weather events?

Several features in the weather pattern across the country influenced what happened in July, Ford says. “A big ridge of high pressure set up across the western U.S., creating a hot dome with record or near-record temperatures there,” he explains. “On the other side of the country, the Bermuda High in the Atlantic set up a bit farther west than normal for July.

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“This setup allowed warm, moist air to flow up from the Gulf of Mexico into the Midwest, buffeted by the ridge on one side and the Bermuda High on the other. Meanwhile, low pressure systems originating as far north as Alaska could penetrate southward without being blocked, due to that same ridge.

“When cooler air from way up north met very warm air from the Gulf, laden with moisture, thunderstorms formed. That’s what gave us these unusual events during July.”

He adds that the El Niño-Southern Oscillation cycle, now in the neutral phase, was not a factor in these events.

Late-summer forecast

As August approached, the ridge forming the hot dome to the west showed signs of breaking out, allowing heat to spread farther east. Warmer-than-normal weather returned for much of the central Midwest, including Illinois and Indiana, over the first weekend of August, Ford says.

“The pattern that set up in July kept temperatures slightly below normal,” he observes. “In Illinois, July averaged about 1 degree F below normal. Before July, temperatures all spring were averaging above normal. It is the primary reason why many crops ran ahead of schedule all spring and through June.”

Now, Ford believes the trend for temperatures in the eastern Corn Belt, including Illinois, will likely return to warmer than normal for August. However, because the Bermuda High isn’t moving, moisture from the Gulf can still flow northward. He anticipates that the chance for occasional thunderstorms and rain will continue into August.