textproduct: Des Moines

KEY MESSAGES

- A few small showers in southern Iowa this afternoon, then clearing by tonight with quiet weather into Monday.

- Thunderstorm chances return at intervals from late Monday into Tuesday night. Severe weather may be possible in northwestern Iowa around Monday evening into early Monday night, then across much of the state on Tuesday.

- A generally active weather pattern continues with lingering rain chances from Tuesday night into Thursday or Friday, but diminishing severe weather chances during that time.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 102 PM CDT Sun Aug 16 2026

A remnant mesoscale convective forecast has drifted slowly eastward near the Missouri/Iowa border today, spreading stratiform rain and isolated thunderstorms across our southern counties through the morning. Most of the rain has now departed, but a few patches of sprinkles and a couple of small showers are lingering this afternoon. These will continue to diminish and end before sunset. Meanwhile, a large surface high pressure area is approaching from the northwest and helping to push/erode thick cloud cover slowly southward, through farther north it is filling in somewhat with diurnally generated cumuliform. The high pressure area will settle across Iowa overnight into early MOnday, providing a brief respite from recent active weather and helping skies to clear further overnight. It will also bring lower dewpoints in the upper 50s to mid-60s, but these will be unfortunately short-lived late tonight into early Monday before rebounding again as modest southwesterly surface flow returns. In the interim, very light/calm winds around sunrise Monday with clearing skies may lead to some potential fog development, though this is somewhat tempered by the lower dewpoints working into the area. Some high-resolution models do indicate patchy fog while others do not, and for now have limited mention in the official forecast to patchy fog in our southwestern areas near the Nish valley, but observational trends will need to be monitored overnight.

A subtle upper level shortwave will move east southeastward over the Dakotas on Monday, with a reflective surface front stretching from around western Nebraska into central Minnesota by Monday evening. With moisture pooling ahead of this boundary SBCAPE of around 1500-2500 J/KG or so will spread across areas just to our northwest, and at peak heating the forcing associated with the approaching shortwave should kick off thunderstorm development in those areas. Deep- layer shear of 40+ KT is forecast and supercells and severe weather will be possible over eastern South Dakota, southwestern Minnesota, and adjacent areas. The frontal boundary will then push into at least parts of our forecast area Monday night, but with the upper level wave pushing eastward toward the Great Lakes and stranding the slowing surface boundary behind, storms should gradually weaken in intensity as they spread into our area, with upper forcing and near-surface instability waning. Mid- level lapse rates also appear less impressive with southeastward extent, supporting a weakening trend. Still, there is some threat of at least isolated severe storms mainly in our northwestern counties around Monday evening, as appropriately outlined by SPC outlooks.

The old frontal boundary that sags in Monday night will likely stall out somewhere across Iowa on Tuesday, as a more robust mid/upper shortwave trough approaches from the west northwest. Stronger destabilization is anticipated ahead of this wave, with SBCAPE of 2000-3000 J/KG developing across much of our area by early to mid- afternoon. Concurrently, 0-6 KM Bulk Shear of around 40-50 KT will overspread the region from the west, with hodographs showing weak curvature and relatively straight orientation. While this presents a favorable synoptic set-up for severe weather potential, questions remain regarding convective evolution. Some model solutions depict lingering cloud cover from decaying Monday night storms that could limit insolation/destabilization Tuesday morning. Other solutions, such as the 12Z NAM, develop additional storms in eastern Nebraska late Monday night and drift them eastward across Iowa Tuesday morning, likewise limiting destabilization ahead of other storms that develop later in the day. In any event, high (70-90%) POPs are maintained on Tuesday, and severe thunderstorm potential will continue to be assessed over the next couple of days. There is also the potential for locally heavy rainfall, particularly in areas that may experience multiple rounds of storms between Monday night and late Tuesday. Once the main push of the second shortwave moves overhead around Tuesday afternoon into the evening, showers/storms should gradually diminish and trend a bit more southward Tuesday night.

LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/

Issued at 1249 PM CDT Sun Aug 16 2026

From Wednesday through Friday, Iowa will continue to reside beneath northwesterly 500 MB steering flow, though which at least two more shortwave impulses will travel overhead. At the surface, however, the old decayed frontal zone should be pushed to our south over Missouri by convective outflows from Tuesday/Tuesday night storms. Additional showers may linger in our southern counties Wednesday into Wednesday night, but then decrease from Thursday onward with generally 10-30% POPs in the extended. The quick passage of a surface ridge along with light northwesterly flow should also allow for somewhat cooler weather, with daily highs generally in the 70s to lower 80s, though dewpoints will likely remain in the 60s to lower 70s. There are some indications that next weekend a larger surface high pressure system will build into the Upper Midwest and Great Lakes region, which if this occurs, may provide more tangible relief from the humidity that has persisted for the past few weeks.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1237 PM CDT Sun Aug 16 2026

Low clouds will affect the area this afternoon, with intermittent MVFR ceilings (FL022-029) possible at FOD/MCW/ALO/DSM in the next couple hours before rising into the VFR range. At OTM ceilings may be lower (FL012-018) and persist longer with light showers in the area, but will then also gradually rise to VFR before 00Z. Thereafter, skies will steadily clear and VFR conditions are forecast for the remainder of the TAF period. There is also a low (20%) chance of fog impacts at some terminals around sunrise Monday, but given the low probability have not advertised this in the 18Z TAFs.

DMX WATCHES/WARNINGS/ADVISORIES

None.