textproduct: Des Moines

KEY MESSAGES

- Storms chances increase over northern Iowa into Tuesday morning, then spread southeastward through the day.

- Additional shower and storm development is expected later Tuesday and through Wednesday, with an increased potential for flash flooding, mainly in urban areas. The severe threat remains low at this time.

- Drier conditions later in the week, with warming into the weekend.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 305 PM CDT Mon Aug 3 2026

A look at surface features this afternoon shows an area of weak high pressure over the Ohio Valley and Great Lakes region, covering much of Iowa yet. A surface low pressure system in relation to an upper level shortwave trough sits over the Dakotas into Nebraska, with a frontal boundary extending from western Minnesota through central Nebraska. These features have resulted in a tightened pressure gradient into western Iowa, along with increased diurnally driven mixing of the PBL, leading to slightly breezy winds, with gusts up to 20-25 mph out of the south/southwest. Satellite imagery shows increasing cumulus development this afternoon, mainly near and east of I-35, but could expand further west slightly before dissipating near sunset. Wildfire smoke is also noted into western Iowa as upper level flow remains out of the northwest, though this should remain aloft. With breaks in the clouds and more of a haze further west, temperatures should continue to warm a bit more this afternoon, with most areas expected to see values in the mid to upper 80s. Winds will decrease into the evening as the sun sets, with surface flow light from the south/southeast into the night. Conditions are expected to remain dry across the forecast area this evening, though the upper ridge over the Upper Midwest departs eastward and the aforementioned trough and surface frontal boundary tracks southeastward into north/northwest Iowa. This system will be the primary focus over the next few days, as shower and storm chances increase over northern Iowa into Tuesday morning, with more broad coverage across the forecast area later Tuesday and especially Wednesday.

For tonight into Tuesday morning, ahead of the aforementioned front, an increase in theta-e advection is indicated, along with a strengthening low-level jet into Kansas/eastern Nebraska/western Iowa. Model soundings however continue to show dry air remaining present overhead given the slowly departing area of high pressure, with most guidance suggesting increasing saturation through the column after midnight and perhaps after 3-4am over north/northwest Iowa. Scattered showers and storms look to remain rather spotty in coverage over the northwest half of the state throughout the morning, with low concerns for severe weather given rather limited instability and weak shear overhead. Into the afternoon, most model guidance indicates the surface boundary to have crossed much of the forecast area, located generally over southern Iowa as this initial round of activity tapers. The primary concern with this activity through the day will be heavy rainfall, given PWATS around 1.75 inches and deep warm cloud depths, though this first wave of shower and storm activity should be progressive enough to limit flooding concerns.

While the surface front looks to be somewhere over far southern Iowa or northern Missouri by late Tuesday afternoon to evening, the 850mb front looks to lag behind, with more uncertainty though on exact location as model guidance is quite varied in location being anywhere from north-central Iowa to south central Iowa in a slight southwest to northeast orientation as it generally stalls out into Wednesday. Further aloft, a broad mid to upper level longwave trough over Canada descends slightly further south into the Midwest, leading to better forcing into Iowa. Additional shower and storm activity looks to develop along and behind this elevated boundary through Tuesday evening and much of Wednesday, with this setup of support for lift aloft and pooling of moisture in the low levels being much more conducive for flash flooding concerns to enter the picture. PWATS in the 1.75 to 2 inch range, deep warm cloud depths and skinny CAPE profiles, as well as parallel flow along the boundary are indicated, leading to higher concern for heavy rainfall and repeated rounds of rainfall leading to a higher potential for flash flooding. While rural areas should largely be able to handle higher rainfall amounts given mature crops, urban areas are of more concern. At this time, most recent guidance indicates more members suggesting the heaviest rainfall amounts over Central Iowa of 2-3 inches possible, while locally higher amounts near 4-5 inches are certainly not out of the question as the higher-end RRFS suggests, considering potential for training storms and several rounds over the same areas. Will continue to monitor trends over the next 24 hours, with increasing confidence more likely as models better grasp this particular time period of concern. The Slight Risk for heavy rainfall from the WPC remains over much of Central Iowa Wednesday, so planning ahead for potential impacts is recommended while remaining in tune to latest forecast updates.

Besides the rain, temperatures will be much cooler Wednesday as thick stratus and northwest winds cover the state, with highs expected to top out in the 70s.

LONG TERM /THURSDAY THROUGH SUNDAY/

Issued at 305 PM CDT Mon Aug 3 2026

As the boundary gradually departs Wednesday, dry conditions are expected to return through the evening. The trend Thursday and beyond shows a period of dry conditions as ridging generally builds across the Western CONUS, with gradual warming occurring as highs return into the upper 80s to low 90s by the weekend. Could see a few shortwaves ride the broader ridge late week and more so later in the weekend that could introduce some potential for showers and storms, though this is low confidence given this being in the long range period of the current forecast, and will continue to keep an eye on trends over the next several days.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 626 PM CDT Mon Aug 3 2026

Shower and thunderstorm chances will increase tonight near KFOD/KMCW and expand into KDSM/KALO on Tuesday. Widespread precipitation is expected in those areas by mid to late afternoon. Cigs will lower as well and will be MVFR at times by the afternoon. Expected VFR conditions at KOTM through the period. The wind will be generally light.

DMX WATCHES/WARNINGS/ADVISORIES

None.