textproduct: Des Moines

KEY MESSAGES

- Showers and thunderstorms are ongoing across southwestern Iowa. There is a low (20%) chance for northward expansion through the morning.

- Heat and humidity continue through Wednesday across Iowa with heat indices nearing 100 degrees across southern and central Iowa.

- Shower and thunderstorm chances return tonight through tomorrow morning. Damaging wind gusts are the primary threat with large hail and locally heavy rainfall possible.

- Wildfire smoke will remain aloft over Iowa through Wednesday.

- On and off thunderstorm chances continue through most of the week.

SHORT TERM /THROUGH TUESDAY/

Issued at 341 AM CDT Mon Aug 10 2026

Current conditions across central Iowa include some patchy to locally dense fog, with the densest of fog confined to the Nishnabotna Valley. Cloud cover across the state will keep the potential for fog (especially dense) relatively low elsewhere. Otherwise, showers and thunderstorms are ongoing across the southwestern corner of the state. The low level jet is kicking these off. The low level jet will move and nose into Iowa around sunrise, yielding to the potential for more widespread showers across southern Iowa through the morning. This would come from a complex of showers and storms making its way across Nebraska, and as it decays it could leak into Iowa during this timeframe.

Continuing through the day today, the heat and humidity will linger. Dewpoints were taken back a little bit and high temperatures were poked down due to the potential for cloud cover and a dense push of smoke aloft. Even with these changes, high temperatures are expected to be in the 80s and 90s with heat indices approaching 90 degrees (northern IA) to 100 degrees (southern IA). As far as precipitation chances through the afternoon go, deterministic guidance suggests that, despite ample instability (2000+ J/kg of MUCAPE), 700mb temperatures are expected to be between 12 and 15C, leading to a strong cap through the day. Combined with weak moisture return, PoPs will remain low during the afternoon and evening hours.

Going into tonight/Tuesday morning, things get more active. A mesoscale convective system (MCS) is forecast to form in the Dakotas during the evening hours and make its way into Iowa. SPC has highlighted northwestern Iowa with a Slight (Level 2 of 5) Risk which is driven by the threat for damaging straight-line wind gusts. There are some uncertainties about how strong the MCS is and how strong it will remain as it moves across Iowa. Compared to the past several nights, convection allowing models (CAMs) are in relative agreement that the MCS will happen, with varying solutions as far as timing and strength. Something of note is how the low level jet sets up tonight. The GFS hints at a much stronger jet (40-45kts) pointed into Iowa, which would imply the MCS stays stronger and raises the potential for severe weather through the night. The NAM and Euro still indicate a favorably oriented jet, but it's not as strong (25- 30kts), which would help dampen the severe threat through the night. The position of the jet also keeps the MCS confined to areas north of I-80 as it moves through Iowa. All this is to say, while there is pretty decent confidence in an MCS occurring overnight, there are still lingering questions about just how strong it remains through the area and the exact timing as it moves through the area. Regardless, there is some level of a damaging wind threat with it. Similar to Sunday morning, if storms can grow taller the damaging hail threat will increase, but for now straight-line wind gusts are the primary threat. Finally, the expected progressive nature of storms will limit the excessive rainfall threat, but high rain rates could lead to an isolated flooding threat, particularly in cities and towns.

Showers and thunderstorms will primarily be out of the area by midday Tuesday, with the potential to linger just through the afternoon. Similar to previous days, with the MCS tracking over northern Iowa, highs will top out in the mid-80s. Elsewhere in the state, highs are expected to be in the upper 80s to low 90s once again. Heat indices across southern and central Iowa will be right around 100 degrees. Some guidance hints at redevelopment in the afternoon and evening Tuesday along the boundary that has been draped across Iowa for the past several days, however this depends on mesoscale details that will be determined by the behavior of tonight's MCS. Once again, shower and thunderstorm chances continue Tuesday night into Wednesday with the potential for another MCS to move through the area.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 206 PM CDT Sun Aug 9 2026

Little change in the upper level pattern as westerlies aloft prevail through at least mid-week before a trough develops over the Western CONUS leading to weak ridging into Iowa. Expect wildfire smoke to persist over Iowa until the trough develops to the west and changes the source region of the upper flow. This smoke remains dense enough for solar filtering and perhaps will result in slightly cooler temperatures than forecast. The little change in the pattern will also keep the surface boundary in the vicinity of Iowa through Wednesday then it will shift a bit south into Missouri. On and off chances for thunderstorms will occur during this period, especially during the overnight hours as the LLJ fuels thunderstorm development in addition to the periodic short wave passages. Thunderstorm chances will continue to end the week despite the arrival of cooler air as an overrunning event of the surface boundary appears possible. Heat index values may eclipse 100 degrees Tuesday and Wednesday over central and southern Iowa but at this time, should remain below headline criteria.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 619 AM CDT Mon Aug 10 2026

Prevailing VFR conditions are expected through most of this TAF period. Locally dense fog has developed early this morning, placing KMCW in LIFR, however this fog should burn off by around 13z. Similarly, while not as dense, fog has developed around KFOD and will burn off around the same time. At KDSM and KOTM, shifting winds are expected through the day, though winds will remain light (under 10kts). Across southern Iowa, scattered thunderstorms are ongoing and are expected to drift east, potentially impacting KOTM briefly this morning. Otherwise, late period, showers and thunderstorms are expected to impact northern terminals. For now, confidence is too low in timing for a TAF mention, but will be addressed in future TAF issuances.

DMX WATCHES/WARNINGS/ADVISORIES

None.