textproduct: Des Moines

KEY MESSAGES

- Showers and thunderstorms across the area should diminish through the afternoon before storm chances return late tonight/early Monday morning.

- Severe thunderstorms and excessive rainfall are possible Monday afternoon and into the overnight hours. Heavy rainfall and training storms may result in flash flooding, particularly in cities and towns.

- Heavy rain and storm chances persist through at least the middle of the week, leading to both river flooding and flash flooding concerns.

SHORT TERM /THROUGH MONDAY/

Issued at 240 PM CDT Sun Sep 13 2026

Showers and a few thunderstorms are ongoing across portions of Iowa. These showers are expected to continue today before diminishing later this afternoon and clearing by sunset. Apart from brief periods of heavy rain leading to localized ponding, this rainfall should be fairly unimpactful. That said, multiple rounds of heavy rainfall are likely and efficient rainfall is occurring with these storms. Most of the night should be clear and cooler with lows in the 50s with some portions in the north having the potential to dip into the upper 40s overnight.

The active weather pattern will continue tomorrow as surface high pressure clears the area early on. There will be two waves of storms, the first coming early in the morning on Monday and the second developing later Monday afternoon and evening. Heavy rainfall is expected with both of these rounds, but the primary severe risk will be later in the day on Monday. Currently, SPC has a Slight (Level 2 of 5) Risk of severe weather for portions of the area. WPC also has a Slight (Level 2 of 4) Risk of excessive rainfall for much of the area.

The severe threat for tomorrow/Monday has a couple of potential outcomes which are dependent on the evolution of storms that form in the very early morning hours of the day. A band of showers and storms should form in eastern Nebraska/western Iowa along an elevated boundary. Once these storms clear the area, a strong Low Level Jet (LLJ) will be in place. Plenty of moisture will be available and CAPE is sufficient for organized storms (~1400- 2000J/kg of MUCAPE). The environment will also be highly sheared with 40-50kts of 0-6km shear available. The uncertainty remains with how the atmosphere recovers after the morning convection, which has strong implications on the severe threats. The two potential scenarios for tomorrow are:

1. The morning convection clears the area, allowing for the environment to recover and take advantage of diurnal heating and allowing some of the stronger winds just above the surface to mix down. Stronger southwesterly to southerly surface winds will lead to a favorable wind profile for surface-based supercells to become tornadic, as well as being capable of producing large hail and damaging winds.

2. The morning convection doesn't clear as quickly, leading to less diurnal heating at the surface. This would keep the environment capped and winds at the surface would be much lighter. This, in-turn would lead to storms being elevated and posing more of a damaging wind and large hail threat.

With either scenario, destabilization across Iowa looks to happen later in the day, leading to a narrow temporal window for organized severe storms. Furthermore, with either scenario, heavy rain remains a threat and this will become a theme over the next few days. More specifics about the heavy rain threat can be found in the hydrology discussion below, as multiple days of heavy rainfall are expected. Specific to Monday's heavy rain threat, strong moisture transport from the Gulf pushes into Iowa with models pointing to a stronger push in the low levels compared to previous runs. PWAT values meet or exceed 2 inches across much of the area. Furthermore, warm cloud depths between 13000 and 15000ft are being modeled, which would lead to very efficient rainfall with any storm. Training storms are also a consideration as storm motions are expected to be parallel to the boundary that sets up before it sags south. Storms are expected to last through much of the night as this front moves. Given all of this, flash flooding is a concern, particularly if several rounds of storms go over any area with lots of concrete (towns and cities).

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 240 PM CDT Sun Sep 13 2026

How far this boundary moves will become the focal point of showers and storms Tuesday. Strong moisture transport is expected to continue and PWAT values will remain rather high through the day. The continued heavy rain potential leads to another Slight (Level 2 of 4) Risk from WPC for excessive rainfall Tuesday and beyond as each successive day will see a threat for heavy rain, with the potential for the heavy rain threat to last through Saturday. The Extreme Forecast Index (EFI) signals at anomalously high QPF values each day, reading around 0.4 or greater until Saturday. The EFI signal is greatest through Wednesday, but the additive effects of several days with heavy rain will lead to both flash flooding and river flooding concerns through the week.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1216 PM CDT Sun Sep 13 2026

Light showers and occasional thunder are spanning much of the area through mid-day, leading to occasional visibility reductions. This activity will continue tracking south and eastward through the afternoon, and has already cleared out of KFOD and KMCW. Conditions completely dry out later this afternoon and evening, with quiet conditions overnight. However, another push of showers and storms will arrive early Monday morning, lifting southwest to northeast across most of the area and last through the end of the period.

HYDROLOGY

Issued at 240 PM CDT Sun Sep 13 2026

Multiple rounds of persistent and potentially heavy rainfall really beginning today and continuing through much of this week is raising concerns for flood and flash flood impacts through the week. Any flash flooding risk with heavy rainfall today and again Monday morning will be fairly localized. This afternoon's rainfall has been rather efficient, but also scattered and not overly intense. Still, some areas have picked up a half inch to an inch of rainfall over western and southwestern Iowa. A lull in precipitation is expected overnight, but another push of moisture and heavy rain is expected Monday morning into mid-day. Again, this rain should be progressive, but PWATs approaching two inches could lead to some localized rainfall amounts of 1 to 2" or even higher if redevelopment occurs on the back side of the initial wing. This locally heavy rain could again lead to ponding water or minor flash flooding tomorrow morning. The widespread nature of this rainfall will also add more water to the overall system.

As we get into Monday night, the flash flooding risk increases thanks to high PWAT values and storm motions along a southwest to northeast oriented boundary. Training storms and efficient rainfall will lead to prolonged periods of heavy rainfall. Flash flooding will become increasingly likely by Monday morning, especially if the heavy rain coincides with urban areas or areas impacted by previous rains. Likewise, some small streams and basins could see rapid responses. However, the location of greatest impact will be heavily contingent on where the mesoscale boundary and training storms set up. This is causing quite a spread among guidance for where exactly the heaviest QPF footprint will reside, ranging anywhere from northern to southern Iowa. For this reason, have held off on a Flood Watch for flash flooding at this time, but will continue to assess the need for one in future shifts.

The perpetual heavy rainfall continues into Tuesday and Wednesday, with more waves of storms possible both days. With cumulative rainfall over the area, it's becoming increasingly possible that we will see the flooding threat expand to rivers as well. GEFS driven Hydrologic Ensemble Forecasting Service (HEFS) 30% exceedance probabilities show rivers reaching action or minor flood stage along multiple rivers in central Iowa. In the top 10% of model solutions, rivers start pushing moderate to major flood stage. This of course would be a higher end, lower probability scenario, but it's a good indicator of the potential residing in this weeks pattern. Of course, variations in the QPF axis, as well as the placement of mesoscale features after each successive round will greatly dictate what happens, but the river flooding component is worth monitoring closely.

DMX WATCHES/WARNINGS/ADVISORIES

None.