textproduct: Des Moines

KEY MESSAGES

- Thunderstorms this morning with isolated to scattered storms this afternoon. The severe weather and heavy rainfall threat has diminished. A damaging wind gust or locally heavy rain could still occur.

- Gusty winds possible early this morning associated with meso- high/meso-low over west central Iowa. Gusts over 40 mph are possible.

- A few storms possible again on Wednesday, mainly over western Iowa. The threat for severe weather is low.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 249 AM CDT Tue Aug 18 2026

Thunderstorms have remained to the north and to the west of Iowa so far this morning. The strongest storms are now entering southeast Nebraska. These storms have maintained cold pool balance and there is even an evident meso-high pressure on the latest surface analysis. These storms are tracking southeast and may still clip far southwest Iowa though the current stability from the lingering surface high will be a challenge and likely result in a weakening along any part of the complex moving into Iowa. Additional storms are moving southeast out of South Dakota. While these storms are not currently severe, these may have a better potential to remain intact as they enter Iowa with the instability axis leaning into northwest Iowa in the next few hours. Overall though, the threat for severe weather and heavy rainfall through today is on the wane. The potential remains for a damaging wind gust this morning associated with storms. In addition, a meso-low has developed over northwest Iowa, likely in response to the meso-high. Gusty winds are possible between these two and there is a pressure gradient near 40 ubars/km that has developed between the two. This may lead to wind gusts greater than 40 mph. This is already showing up around Sioux City where personal weather stations are recording gusts of 30-40 mph. The wind did turn more southeast when this occurred so it is possible this could resemble more of a wake low as it is near the back edge of the eroding stratiform precipitation.

The showers and thunderstorms this morning are likely the main period of precipitation. Some recovery does occur this afternoon, mainly across northern Iowa and may result in isolated to scattered storms. The recovery includes skinny CAPEs through the instability layer so not much potential for strong parcel accelerations. With this weaker CAPE, any storm tops will likely be strongly sheared due to quickly increasing speed shear aloft. Perhaps that can maintain updraft/downdraft balance. The heavy rain threat is decreasing as well. Moisture recovery has not been quite as strong as previously advertised and now max PWAT values are expected to be closer to 1.75 inches and with lack of training potential or vigorous convection, widespread heavy rain isn't likely. The main focus for storms later today will be along the retreating warm front across Kansas where the primary instability axis will be located. Trending drier tonight while a few showers and storms remain possible over western Iowa on Wednesday.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 308 PM CDT Mon Aug 17 2026

Additional precipitation chances are in the forecast on Wednesday as shortwave energy continues to move through the otherwise northwesterly upper flow. Drier conditions are then forecast on Thursday as another high pressure moves across before returning again Thursday night into Friday with another push of energy. This seems to be a common pattern into the weekend with about every other day dry- precipitation chances but with overall lower confidence in the placement and timing at this range. Temperatures remain pleasant this week in the the 70s to 80s.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1237 PM CDT Tue Aug 18 2026

Scattered shower and thunderstorm redevelopment remains possible this afternoon to evening but confidence in impacts at TAF sites remains too low to move mentions from previously issued prob30 groups. In some cases confidence in impacts at a terminal is falling with highest confidence close to KMCW, but maintained at other sites for continuity. If clearing can occur, some fog may be possible overnight, especially at eastern sites KOTM/KALO but with questions in cloud cover, uncertainty remains in extent of impacts. At least scattered MVFR CIGs are expected this afternoon and could become BKN at times if a shower/storm were to occur. Gusty winds may also occur near storms with otherwise winds becoming light and variable tonight.

HYDROLOGY

Issued at 819 AM CDT Tue Aug 18 2026

Overall flood threat from today's event has decreased. QPF amounts have trended downward, and the heaviest amounts have trended away from locations that are most susceptible to flash flood-like hydro responses (mainly from along the I-80 corridor south to US Hwy 34, with a secondary maximum extending from the Des Moines to Fort Dodge areas). Thus, minimal short-term hydrologic responses are expected, and tools like the National Water Model short-range output concur.

Minimal longer term hydrologic responses like on rivers are expected as well. In general, less overall runoff is expected, leading to less than expected rises on area streams. Our QPF ensemble hydrographs, HEFS and the National Water Model medium-range output all concur as well.

DMX WATCHES/WARNINGS/ADVISORIES

None.