textproduct: Des Moines

KEY MESSAGES

- Strong to severe storms continue tonight into the morning hours. Damaging winds, hail and heavy rain are the main concerns, but tornadoes are also possible.

- Storms today through Friday may lead to flooding or flash flooding concerns, especially in areas impacted by multiple rounds of heavy rainfall.

- Uncertainty remains with the forecast into the holiday weekend, but hot and humid conditions persist with thunderstorm chances at times.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 407 PM CDT Thu Jul 2 2026

A rather eventful forecast remains in place now through the next 24 to 48 hours, as a hot and humid air mass continues to bring potential for thunderstorms and muggy conditions through the end of this week and early in the weekend.

Our most immediate concerns are the storms ongoing right now, as a mesoscale boundary sags southward over the northern half of Iowa. A moist and unstable air mass with 3000+ J/kg of instability sits over much of central into eastern Iowa, but the best effective wind shear around 40 to 45 kts is in place along the mesoscale boundary. All severe hazards are possible with these storms, including tornadoes generally in proximity to the boundary where better vorticity is available to the storms. Likewise, damaging winds and hail are also possible, with the highest threat being the damaging winds. At least scattered storms are expected to persist through much of this afternoon and evening, especially as the low level jet ramps up overnight. With the east northeast storm motions, and training development along the boundary expected through the evening, heavy rainfall also remains a concern as this activity persists into the evening. Rainfall amounts of 1 to 3" have already been observed over northern Iowa, with additional storms expected through the evening and overnight, which would only exacerbate conditions. A Flood Watch has been issued for much of northern Iowa. Will also be watching for a southern expansion of the heaviest rainfall, especially as storms persist through the day and evening.. More on the flooding concerns in the hydro discussion below.

As we get late into tonight, storms developing to our west over Nebraska and South Dakota are expected to evolve into a mesoscale convective system (MCS) which will run along the mesoscale boundary, fueled by a 45+ kt low level jet. This MCS arrives in western Iowa early Friday morning, bringing the potential for damaging winds and more heavy rainfall along similar areas to today. As it tracks eastward, it will eventually lose support from the low level, but the 2000 to 3000 J/kg along the boundary and a strong enough cold pool would help the storms persist all the way across central Iowa. Of course, this Friday morning MCS will be dependent on how mesoscale features evolve overnight, meaning the exact path and evolution will be heavily dependent on how this afternoon plays out. Regardless, the signal and environment is there for a complex of storms to pass through the state.

Assuming the morning MCS comes to fruition, conditions will likely stabilize some through Friday morning. However, the overall environment generally remains unchanged with strong theta-e advection continuing. Atmospheric recovery is expected through the day and more thunderstorm activity will likely develop into Friday afternoon, especially if there are any leftover outflow boundaries and/or mesoscale circulations over Iowa. Instability and shear will once again be sufficient for a few strong to severe storms capable of producing damaging winds and hail, as well as a brief tornado along any boundaries that set up. Likewise, the high precipitable water environment will promote heavy rain. This risk looks to shift farther south than today's, but any areas or basins that receive multiple rounds of rainfall could be at risk of isolated flash flooding and/or rises on creeks and rivers.

In addition to the thunderstorm chances, heat indices will once again approach the upper 90s to near 100. However, convective debris leftover from the overnight storms, as well as any additional development, will likely help keep temperatures cooler over much of Iowa on Friday. Therefore, have decided to only extend the far southern portions of the Extreme Heat Warning across southern Iowa through Friday. It will still be muggy, but likely not to the extremes of earlier this week.

LONG TERM /SATURDAY THROUGH THURSDAY/

Issued at 407 PM CDT Thu Jul 2 2026

The synoptic pattern begins to transition to a more zonal flow pattern through the day Friday and into the weekend. This generally keeps the warm and moist conditions going through the weekend, although some reprieve may be on the horizon. Models are currently depicting a shortwave passing through the state Friday night into Saturday morning, bringing another MCS across Iowa. This system will likely ride along the mesoscale boundary/instability gradient (similar to tonight's), which will likely be farther south in the state. As this occurs, damaging winds and heavy rainfall will accompany it, again bringing severe weather and flash flood concerns Friday night into the morning of Independence Day. However, with the less persistent synoptic pattern, conditions seem to stabilize at least through the day on Saturday. The boundary will be pushed either into southern Iowa or northern Missouri, acting as the focal point for redevelopment on the afternoon and evening of Independence Day. Therefore, the southerly extent of the Friday night into Saturday morning storms may be able to spare much of Iowa from storm chances later in the day Saturday. This would also lead to slightly cooler conditions, albeit still warm in the upper 80s. There is still a lot to happen between now and then, so stay tuned to the forecast for the latest on the Independence Day forecast! Warm and humid conditions then persist into the end of the weekend and early next week, although still not to the extremes of the beginning of this week.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1225 PM CDT Thu Jul 2 2026

TAFs are a combination of VFR and MVFR as showers and thunderstorms are moving across northern Iowa bringing impacts to KFOD, KMCW and KALO. KDSM and KOTM are spared from the low CIGS from ongoing convection but diurnal cumulus clouds around 4K ft are starting to develop. Through the remainder of the afternoon into the overnight, shower and storm chances are expected to exist but there could be a brief lull in activity toward 06Z before showers and storms increase in coverage again. By 14Z, shower and storm chances will start to wane from northwest to southeast through the end of the period. Any shower or storm could bring localized gusty and erratic winds; as well as, brief category reduction.

HYDROLOGY

Issued at 407 PM CDT Thu Jul 2 2026

Flash flood and river flood concerns exist over at least the next couple days due to heavy rainfall potential mentioned above. Greatest concerns are across northern Iowa mainly coincident with the flash flood watch. Main flash flood concerns would be in cities and towns. Soil moisture in some areas has significantly increased due to heavy rain over the past couple days. Additional rainfall combined with relatively short soil recovery times may lead to more runoff than we have recently seen, especially if it falls in those areas, increasing the flash flood risk to within flash flood watch criteria. Lower risk of flash flooding exists farther south into central Iowa. Ponding looks to be the most likely outcome at this time. If flash flooding occurred then it would again be most likely in cities and towns.

Flash flood concerns continue into Friday with more heavy rain possible. Confidence is relatively low in exact placements and amounts. If the weather evolves tonight as expected then the greatest risk on Friday would likely be along and north of the US 30 corridor, with lower risk farther south again.

River flooding would tend to be a longer term concern, depending on heavy rain evolution over the next couple days. National Water Model, HEFS and QPF ensemble hydrograph output suggest the most likely scenario would be minor to significant within-bank rises on many streams north of US 30, with a couple locations possibly seeing minor flooding. If rainfall is higher than expected then locally higher river levels would be possible.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Friday morning for IAZ004>007-015>017- 023>028-033>039. Extreme Heat Warning until 10 PM CDT this evening for IAZ059>062-072>075-082-083. Extreme Heat Warning until 10 PM CDT Friday for IAZ084>086- 092>097.