textproduct: Des Moines

KEY MESSAGES

- Rain continues through much of the day today.

- A reinforcing push of rain and thunderstorms arrives later this afternoon and evening, bringing heavy rain and flash flood potential. The prolonged rainfall and already saturated conditions may lead to river flooding as well.

- Rain and storms diminish from northwest to southeast through the day on Thursday, giving way to cooler and drier conditions into the weekend.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 328 PM CDT Wed Sep 30 2026

The current surface analysis places a stationary boundary over the Central Plains, including Iowa. This boundary has been the primary focal point for ongoing precipitation across the region. To the southwest, the remnants of Hurricane Polo have moved onshore and transitioned into an extratropical low. This surface low is centered over the High Plains of Texas, tracking along the stationary boundary. Statewide surface observations show widespread rainfall across the southern half of Iowa, with southwesterly flow maintaining temperatures in the upper-60s to lower-70s.

Through the remainder of the afternoon and overnight, the upper- level trough absorbing the remnants of Polo will continue to eject northeastward, spreading heavy rainfall across central Iowa. Recent model guidance shifted the heaviest QPF axis slightly northwestward, but overall impacts remain unchanged as forecast parameters meet climatological maxima. From a hydrological perspective, all factors align for a heavy rain event that could cause areal flooding and subsequent river flooding. Given recent rainfall, river levels are already responding rapidly. Abundant tropical moisture, PW values well above climatological normals, and low-level flow parallel to the boundary combine to drive this severe hydrological event. This could potentially make September 2026 the wettest September on record for Des Moines (DSM) while pushing several local rivers into action and minor flood stages.

As the core of the surface low tracks through the area overnight into Thursday morning, a surface cold front will push southwestward into the region, shunting the tropical low east of the area by Thursday afternoon. Showers will gradually dissipate from northwest to southeast throughout the day. Behind the front, soundings indicate steep low-level lapse rates without a cap, and high BUFKIT momentum transfer values across northwestern Iowa favor strong north- to-northwesterly post-frontal winds. Significantly cooler, fall-like temperatures will follow in the wake of the front.

A stationary front over the Central Plains is interacting with tropical moisture and an upper-level trough absorbing the extratropical remnants of Hurricane Polo, generating widespread heavy rainfall and potential flooding across Iowa through Thursday morning. As the surface low moves out on Thursday, a cold front will clear the precipitation from northwest to southeast, bringing strong gusty northwesterly winds and cooler temperatures to the region.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

Issued at 328 PM CDT Wed Sep 30 2026

The extended forecast period is expected to mark the first true transition to fall-like weather. Behind Thursdays cold front, surface high pressure will build back into the region, bringing several days of dry weather and cooler temperatures. Previous forecast iterations depicted a shortwave diving southeastward toward the upper Mississippi River Valley, but this afternoons model guidance has largely removed that feature, leaving the area mostly dry until precipitation chances return late in the period.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 646 PM CDT Wed Sep 30 2026

VFR to LIFR conditions are in place across the area early this evening with rain ongoing through much of central and southern Iowa. This rain is expected to continue, and even strengthen in intensity tonight through the overnight which will drop visibilities at times, potentially even lower than advertised in the current TAFs. Ceilings will also become largely IFR to LIFR to go along with the rain and any potential fog. Have limited thunder mentions in the short term with thunder/lightning potential back closer to the surface low and may only affect southern sites KDSM, maybe KOTM late overnight into Thursday morning. Timing in all cases (rain/visby/cig/thunderstorm) may still need further adjustments and will watch trends closely. Rain gradually ends northwest to southeast as a cold front moves through the area on Thursday with gradually improving ceilings behind. Additionally, winds out of the north will increase behind the front bringing breezy conditions on Thursday.

HYDROLOGY

Issued at 330 PM CDT Wed Sep 30 2026

All types of flooding, including flash, areal and river, remain possible as additional moderate to heavy rain falls across much of the CWA. Rain across the southern CWA last night led to more significant responses than normal for the amount of rain that fell, which shows the degree of ground saturation.

River flood warnings have been issued for locations where we have high confidence (at least 80%) of reaching at least flood stage. We mentioned larger basins where confidence is lower, in our going flood watch instead of issuing individual river flood watches for those locations. Refer to the National Water Prediction Service at weather.gov/desmoines/water for the latest river observations and forecasts.

The Raccoon River basin will be among the more tricky forecasts. Recent rainfall in much of that basin will lead to faster and more significant runoff. Competing factors are nudging the river forecasts higher and lower especially in that basin. If the rain falls farther south then it will tend to lower the crests especially on that stream.

Flash flooding remains possible, especially in urban areas including creeks and smaller streams. It includes Walnut and Fourmile Creeks in the Des Moines area. Seasonally high soil moisture will lead to faster and more significant runoff than normal. Given the relatively small size of those basins, they will be more affected by rain location and amounts. Thus although reaching flood stage is not a certainty on those streams, it is also nonzero, thus will have to be monitored.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch through late Thursday night for IAZ024>028-033>039- 044>050-057>062-070>075-081>086-092>097.