During the week of June 17th, a robust upper-level ridge settled over the eastern United States. As this ridge expanded, temperatures soared across the Midwest. The combination of hot air temperatures and high dew point values pushed the heat index from the upper 90s to the low 100s. Overnight lows remained warm, breaking daily records in several Midwest locations. The National Weather Service issued Excessive Heat Warnings and Heat Advisories to address the dangerous conditions.

Drought Conditions and Rapid Onset Drought

While drought conditions had improved from late winter through spring, the heat and humidity triggered rapid onset drought in parts of the Ohio Valley. The Weather Prediction Center highlighted risk areas in Illinois, Indiana, and Ohio. Within a two-week period, Abnormally Dry to Moderate Drought conditions developed.

As drought expanded across the Ohio Valley, the Upper Midwest faced heavy rainfall and catastrophic flooding. Multiple low-pressure systems moved across the Northern Plains and Upper Midwest from June 21 to 22. A stationary warm front over northern Iowa and southern Minnesota became the focal point for intense rain and thunderstorms. Portions of Iowa and southern Minnesota reported rainfall amounts of 8-11 inches, with some areas in eastern/southeastern South Dakota receiving up to 11.52 inches. Flash flood and flood warnings were issued due to the rapid accumulation of rain.

River Levels

Many rivers and streams in the affected area reached Moderate to Major Flood stage levels. As of June 30th, several rivers in northern Iowa and southern Minnesota were still experiencing significant flooding.

The upper-level high that had brought widespread heat earlier in the month retreated westward, allowing for troughing and a northwest flow to develop across the Midwest from June 24th to June 26th. During this period, several mid to upper-level waves of energy traversed the region. As the waves moved through an atmosphere with abundant moisture and strong instability, they sparked multiple rounds of severe thunderstorms, beginning early on Tuesday, the 25th, and continuing through Wednesday morning, June 26th.

Initial Round (Tuesday Morning): This first round of storms impacted areas in northern Illinois, southern Michigan, and northern Indiana. It brought locally damaging winds with it.

Round Two (Tuesday Afternoon and Evening): Eastern Illinois, south-central/southern Indiana, and northern Kentucky experienced severe storms. Notably, this line caused significant tree damage at Indiana University in Bloomington, IN, and blew the roof off a barn in western Indiana. Nearly 100,000 people were left without power across western and south-central Indiana due to this storm.

Round Three (Tuesday Evening): Northwestern Illinois and central/eastern Iowa faced additional storms. While most of these produced damaging winds, a few tornadoes were reported in Iowa.

Final Round (Late Tuesday into Wednesday): Starting small in eastern Nebraska, this system grew overnight into a large MCS (Mesoscale Convective System). By Wednesday afternoon, it had produced damaging winds extending into Arkansas and Oklahoma.