textproduct: Des Moines

KEY MESSAGES

- A Flood Watch remains in effect through this afternoon as lingering heavy rain threats persist through this morning.

- Many rivers and streams south of Highway 30 and along/north of US 34 have seen rises, mostly within bank, but a few locations have reached or exceeded minor flood stage.

- Diminishing showers/storms through the day today into this evening before coverage of storms increases after midnight into Thursday morning.

- Trend towards the heaviest rainfall late this week pushing over northern Iowa and north, but saturated soils farther south leave conditions susceptible for flash flooding and potentially further stream rises.

SHORT TERM /THROUGH THURSDAY/

Issued at 340 AM CDT Wed Sep 16 2026

The forecast period begins with the area situated between two main synoptic features while remaining under the influence of surface high pressure. Regarding the first feature, yesterdays cold front has passed through the CWA, but its impacts persist with ongoing showers and thunderstorms across Missouri and southeastern Iowa. To our northwest, a second cold front, associated with the persistent upper-level trough and surface low that pushed yesterdays front through, is moving southeast from the Northern Plains. Additionally, a surface wave is noted over the High Plains of western Texas. Locally, showers and isolated thunderstorms are beginning to lift northward back into the area from Missouri. While heavy rain is not anticipated initially, this additional round of rainfall will maintain moist antecedent conditions ahead of subsequent rounds of showers and storms.

Through the remainder of the morning and the rest of today, the stationary boundary will begin lifting north as a warm front, supported by an upper-level trough moving onshore along the California coast. This trough will amplify the downstream flow, leading to upper-level height rises and a gradual decline in PoPs through the afternoon. However, PoPs will remain around 30 percent or less through late this evening, primarily over the southeastern CWA. With decreasing precipitation chances, a temporary reprieve from heavy rainfall is expected today, allowing the Flood Watch to expire on time.

This break will be brief, as the aforementioned Texas disturbance lifts north, driving the warm front across the region late tonight through Thursday. This system will introduce another round of potentially heavy rainfall overnight. Forecast soundings ahead of the boundary exhibit classic heavy rainfall signatures, with precipitable water and integrated vapor transport values climbing toward the 99th percentile to maximum of local climatology. Furthermore, a 25 to 35 knot nocturnal LLJ will advect deep moisture into the region, serving as a primary focus for convective development and maintenance. The highest rainfall totals through the end of the period are currently forecast across Missouri; however, if the boundary lifts further north or convection over-performs Wednesday night into Thursday, these higher totals could extend into areas along and south of the I-80 corridor.

In summary, a short break in precipitation is expected today under very weak high pressure as yesterdays cold front exits. However, a disturbance lifting from Texas will drive a warm front into the region tonight through Thursday, bringing another round of potentially heavy rain supported by high moisture levels and a strong low-level jet.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Issued at 253 PM CDT Tue Sep 15 2026

Similar to Wednesday, whatever showers and storms early Thursday look to become less common through the day as forcing weakens. This will be in part as the ridge over the southeastern US bulges a bit poleward, which pushes the upper level kinematics and track of the nebulous vorticity piece away from Iowa. Further, low pressure over the High Plains look to surge the elevated warm front well north of the state with the highest rainfall amounts now trending northward to northern Iowa if not points farther north over South Dakota and Minnesota. This focus of rainfall may remain north Friday night into Saturday. Meanwhile, a substantive trough over the interior West will push eastward on Friday, which will finally shunt the ridge southeastward, but also bring the return of favorable heavy rainfall parameters this weekend. This front should bring drier conditions at some point, eventually, next week in what is an overall wet and active pattern until then.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1028 PM CDT Tue Sep 15 2026

Showers and storms are still forecast across southern and parts of central Iowa through this TAF period. Timing, however, has slowed from previous TAF periods and is reflected in the KOTM and KDSM TAFs. After showers and storms clear the area around midday Wednesday, MVFR to IFR ceilings will move into Iowa with impacts expected at all terminals through the remainder of the TAF period. Another thing of note this period is the potential for patchy fog impacting KFOD through the morning hours should cloud cover not fill in as quickly as forecast. Winds should remain fairly light through the overnight hours before shifting to being from the east by 12z/7am and remaining around or under 10kts.

HYDROLOGY

Issued at 253 PM CDT Tue Sep 15 2026

Although flash flood and river flood concerns persist this week, the overall threat decreased from Monday. In the short term (through tonight), flash flooding remains a threat mainly along and south of US Hwy 30, and along and north of US Hwy 34, where top-layer soil moisture saturation percentages are highest. Additional heavy rain through tonight may lead to ponding and lower end flash flooding as far south as the MO border, where amounts and rates may be higher. At this time, significant flash flooding is not anticipated.

Some rivers and streams have increased significantly from last night's rain. These elevated stages and flooding will remain a concern through at least the end of this week. The NBM-forced National Water Model (NWM) with 10 days of QPF agrees, suggesting significant within-bank rises on many streams mainly between US Hwy 30 and US Hwy 34, with some minor flooding possible. The GEFS-driven Hydrologic Ensemble Forecasting Service (HEFS) basically agrees as well, however its probabilities decreased from Monday, reflective of lower trending QPF. The 50% exceedance probabilities show multiple streams reaching action stage or minor flood stage in central IA. The 30% exceedance probabilities show more pervasive minor flooding with a few locations at moderate flooding. The 10% level shows more pervasive moderate flooding with a few locations at major flooding. Variations in QPF location and amounts may impact the probabilities, so people should continue monitoring for river flood potential.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 1 PM CDT this afternoon for IAZ057>062- 070>074-081>084-092>095.