08/30/2026
I am keeping a very close eye on Tuesday as the combination of increasing heat, humidity and a very unstable atmosphere could set the stage for multiple rounds of thunderstorms across portions of Iowa and eventually into Illinois.
Before we even get to Tuesday, the heat and humidity will become increasingly noticeable. Heat index values around Muscatine could climb to near 105 Monday, around 104 Tuesday and remain around 104 Wednesday. That surge of heat and moisture will provide a tremendous amount of fuel for thunderstorms once disturbances begin moving along the northern edge of the heat ridge.
The first opportunity for thunderstorms could actually arrive during the overnight hours Monday night into Tuesday morning. There are indications that thunderstorms may develop farther west and then travel east or southeast across portions of Iowa during the early morning hours Tuesday.
Right now, I would watch approximately 3 AM through 10 AM Tuesday for that first potential round, although the exact placement and timing will continue to change. Some locations could wake up to thunderstorms Tuesday morning while others may completely miss that first round.
Any morning thunderstorms could produce frequent lightning, gusty winds and locally very heavy rainfall. Exactly how widespread that activity becomes will also have a major impact on what happens later Tuesday.
If Tuesday morning thunderstorms move through quickly enough and we are able to get several hours of sunshine afterward, the atmosphere could reload very quickly.
That is where my concern begins increasing for Tuesday afternoon and evening.
With temperatures climbing, humidity increasing and a very unstable atmosphere developing, thunderstorms that form later Tuesday could strengthen rapidly. There also appears to be enough changing wind speed and direction with height to allow storms to become organized instead of simply producing ordinary summertime thunderstorms.
At this point, I am watching approximately 2 PM through midnight Tuesday for the main afternoon and evening severe-weather window across Iowa, with the greatest concern potentially developing during the late afternoon and evening.
For eastern Iowa, I would currently watch approximately 4 PM through 10 PM Tuesday, with the threat potentially reaching the Mississippi River and portions of western Illinois approximately 6 PM through midnight.
Those times are NOT locked in yet. Where morning thunderstorms occur, how quickly clouds clear, where boundaries are left behind and exactly where afternoon storms initially develop will determine whether those windows need to be moved earlier or later.
If storms are able to remain more isolated initially, large hail and damaging wind gusts would become concerns. There could also be enough organization for some storms to develop rotation, so an isolated tornado cannot be completely ruled out at this stage. I am not making tornadoes the primary concern right now, but it is something I will continue watching as we get closer.
As storms become more numerous Tuesday evening, they could eventually merge into larger clusters. If that happens, damaging straight-line winds could become an increasingly important concern as storms move east toward eastern Iowa and eventually western Illinois.
Very heavy rainfall will also be possible. With the amount of moisture expected to be available, stronger thunderstorms could produce extremely heavy downpours over short periods of time. If multiple thunderstorms follow similar paths, localized rainfall totals could add up quickly.
The biggest question for Tuesday continues to be how the morning round affects the atmosphere later in the day. If widespread clouds and thunderstorms linger into the afternoon, that could reduce the severe-weather potential. If the morning activity moves away and we break into several hours of sunshine, instability could rebuild rapidly and the afternoon/evening threat would become considerably more concerning.
I am also starting to keep an eye on Thursday. There are early indications that another corridor of showers and thunderstorms could develop, with some of the heavier rainfall potentially becoming focused along and east of the Mississippi River.
It is much too early to start putting rainfall amounts or an exact timeframe on Thursday, and the location of that heavier rainfall corridor could certainly shift. However, with plenty of moisture remaining in place, any repeated thunderstorms could produce locally significant rainfall. This will be another period worth watching, especially for portions of western Illinois and areas farther east.
So right now, Tuesday remains my primary concern for strong to severe thunderstorms and locally heavy rainfall, but Thursday is beginning to show up as another day to watch for potentially heavier rain along and east of the Mississippi River.
There is still plenty that can change over the next several days. I will continue going through everything as new information comes in and will tighten up the timing, areas of greatest concern, severe-weather threats and heavy-rain potential as confidence increases.
Forecast is sponsored by Jessica Jessica Yoder & Sarah Bigley, Realtorsona Realty, Inc.
