textproduct: Des Moines

KEY MESSAGES

- Moderate to heavy rainfall continues this morning. Flash flooding remains possible, and river flooding likely.

- Rain this morning tapers off from northwest to southeast through the day today, with potential for an additional 1 to 2 inches over southern into southeastern Iowa this afternoon.

- Once rain ends across the area today, cooler, drier and breezier conditions develop with dry, fall-like weather through the weekend.

SHORT TERM /THROUGH TONIGHT/

Issued at 216 AM CDT Thu Oct 1 2026

Heavy rain is ongoing early this morning, as the low pressure formerly known as Hurricane Polo makes it's way into western Iowa. Flash flood warnings litter eastern Nebraska into western Iowa where a slow moving, convectively driven line of storms brought efficient rainfall to the area. Rainfall amounts reported out of the Omaha area have ranged from 4 to as high as 8 inches with this line. Upon it's arrival in the DMX forecast area, the line has since fallen apart, but the remaining vort max is still slowly pushing across the area. Fueled by a moisture rich low level jet, this vort max is producing a swath of heavy rainfall with efficient 1-2 in/hr rates. While rates likely won't be as robust as the more convectively driven mode seen to our west, the less progressive nature of this heavy rainfall will allow amounts to rack up quickly. Model guidance continues to show a swath of 2 to 4 inch rainfall falling out of this, with embedded pockets up to 6 inches. Current radar trends would suggest this band is going to set up in a roughly west southwest to east northeast line, following along US Highway 30 west of Ames, passing through the Ames area, then drifting slightly north of highway 30 up towards the Waterloo/Cedar Falls area. This rainfall will likely lead to ponding and flooding throughout north central Iowa, as heavy rain falls on already saturated soils. The Flash Flood Watch continues through this evening, although some adjustments to the watch are likely as rain begins to end today.

After the vortmax pushes through later this morning, the trailing cold front will begin to push southward, ending the rainfall from northwest to southeast through the day. Barring a few elevated showers, much of the forecast area will see rain ending by noon, if not sooner. Before completely pushing out of the area this afternoon, we may see showers and even a few storms fester along the boundary in southern and southeastern Iowa. These will have the potential to bring another 1 to 3 inches to southeastern Iowa, although it's possible this secondary band ends up south and east of our forecast area. Regardless, given the widespread rain that fell yesterday and saturated soils over southern Iowa, WPC has maintained a slight risk for excessive rainfall (level 2 of 4) to account for this secondary swath of rain in southeastern Iowa later today.

Behind the cold front today, conditions over Iowa will be drying out and cooler air filling in. Slightly enhanced pressure gradients combined with the cooler, descending air mass will lead to some breezy post-frontal conditions today. Northerly winds of 15 to 20 mph are expected today, with gusts up to 30 mph especially over northern Iowa.

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 /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1108 PM CDT Wed Sep 30 2026

VFR to LIFR conditions remain to start the period and will continue through the overnight with IFR to LIFR conditions persistent during the expected rain through the overnight. The heaviest rain is expected during this time period which will cause visibility drops at times due to the intensity of the rain, 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 kept limited thunder mentions at KDSM and will monitor closely should thunder remain long enough to affect KOTM as well 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 216 AM CDT Thu Oct 1 2026

All types of flooding, including flash, areal and river, remain possible as additional moderate to heavy rain falls across much of the CWA. Responses on area rivers are already ongoing with the rainfall that's fallen through early Thursday morning, with additional rain still on the way.

River flood warnings have been issued for locations where we have high confidence (at least 80%) of reaching at least flood stage. A handful of river flood watches have been introduced at rivers where confidence in flooding is relatively lower. Refer to the National Water Prediction Service at weather.gov/desmoines/water for the latest river observations and forecasts.

The Raccoon River basin will likely be impacted by rainfall this morning, but will see a more delayed response with the heaviest rain falling farther north (upstream) in the basin. Recent rainfall in much of that basin has already primed rivers for a response, with additional water fallen or falling now early this morning.

Flash flooding remains possible through this morning, especially in urban areas including creeks and smaller streams. Seasonally high soil moisture will lead to faster and more significant runoff than normal. With the heavy rain threat shifting slightly northward, quick responding streams in the Des Moines metro (Walnut and Fourmile Creek) seem less likely to see significant responses, but Ioway Creek in Ames may still end up under the heaviest rainfall and will be monitored closely through the morning.

DMX WATCHES/WARNINGS/ADVISORIES

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