textproduct: Des Moines

KEY MESSAGES

- Heavy rainfall with the potential for flash flooding will persist through cold frontal passage this afternoon.

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

SHORT TERM /THROUGH WEDNESDAY/

Issued at 314 AM CDT Tue Sep 15 2026

The early overnight surface analysis reveals an active synoptic pattern across much of the central CONUS. An occluding 993 mb surface low is centered over south-central Canada with a trailing cold front oriented south-southwestward through the Central Plains to the Four Corners. A secondary surface low is riding along the front, while a stationary boundary extends southeastward across much of the southern US. Meanwhile, yesterdays surface high has shifted eastward and is centered over the northern Mid-Atlantic. Locally, a combination of the approaching cold front and the secondary surface low continues to drive showers and thunderstorms eastward across the region, producing showers and thunderstorms with heavy rainfall rates.

Through the remainder of the overnight period and into the day, the cold front will slowly track through the DMX CWA, gradually pushing the precipitation out of the area. Recent model runs show slight variability regarding exact timing, but the consensus brings FROPA through the region by early afternoon. Prior to FROPA, showers and thunderstorms will persist across the southern half of the forecast area. High precipitation efficiency is evident, with rain gauges reporting rates of 1.5 to 2.5 inches per hour as the core of the activity moves through the Des Moines metropolitan area and points along the I-80 corridor. While widespread flash flooding is not currently observed, a strong LLJ continues to transport rich moisture into the region. With low-level flow aligned parallel to the front, training convective cells remain likely until frontal passage, elevating the threat for flash flooding.

Behind the front, a very brief lull in activity is expected as weak surface high pressure builds in from the north today. However, upper- level dynamics associated with the right entrance region of a departing jet streak will lift the precipitation shield back northward, bringing rain chances back to the area late Tuesday night into Wednesday. Abundant moisture and strong synoptic lift will keep heavy rainfall ingredients in place over already saturated soils, maintaining a heightened flood risk. Consequently, a Flash Flood Watch remains in effect through Wednesday afternoon, and the WPC maintains a Slight Risk for Excessive Rainfall across much of the forecast period.

An active frontal system and surface low will bring heavy rainfall and potential flash flooding to the area through early afternoon before a brief break in precipitation occurs behind the front. However, upper-level jet dynamics will quickly push moisture back northward late Tuesday night into Wednesday, prolonging heavy rain risks over saturated ground and keeping the Flash Flood Watch active.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 209 PM CDT Mon Sep 14 2026

On a broad scale, Iowa will reside in generally fast flow around mid- level high pressure over the Deep South/Southeastern US, which will migrate slowly back to the west by week's end. In this fast flow, there will be a few shortwave troughs that pass through along with fragmented vorticity pieces, which will interface with a surface and elevated boundary draped across the region if not the state at times. The pattern is thus conducive to additional rounds of rainfall on what will be increasingly saturated soil and thus increased risk of flash flooding with each successive round of rain. This rainfall will route into waterways and lead to increasing river levels with additional details in the hydrology discussion below.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1253 AM CDT Tue Sep 15 2026

Showers and thunderstorms continue along and southeast of a line from DSM to ALO. Other scattered showers are developing just west of FOD. This is expected to continue through the night before activity settles across southern IA later this morning. Generally VFR conditions can be expected, with MVFR or brief IFR conditions in the heaviest showers and storms. The TS threat should diminish area wide by 11Z. Light winds overnight will shift north behind a cold front Tuesday morning.

HYDROLOGY

Issued at 210 PM CDT Mon Sep 14 2026

Flash flood and river flood concerns continue this week due to forecast multiple rounds of moderate to heavy rain. Flash flooding is more of a concern in the short term (later today into Tue morning). Short term National Water Model rapid onset flooding (ROF) guidance continues suggesting the greatest risk of flash flooding mainly between US Hwy 30 and the MO border, or roughly the same area included in the current flood watch. Most likely scenario will be ponding and low end flash flooding, however if QPF overachieves then pockets of more significant flash flooding may occur especially over urban areas. Since general storm motion is anticipated to be from W- E or SW-NE, small stream basins oriented in those directions would be most susceptible to flash flood impacts especially with training thunderstorm activity. Additional heavy rain will prolong flash flood concerns beyond Tue morning.

Longer term, river flood concerns exist too. The NBM-forced National Water Model (NWM) with 10 days of QPF shows significant within-bank rises on many streams across roughly the southeast half of the CWA, with some minor flooding possible. The GEFS-driven Hydrologic Ensemble Forecasting Service (HEFS) basically agrees, with 50% exceedance probabilities showing several 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 moderate to major river flooding across much of the southeast half of the CWA. Variations in QPF location and amounts as well as mesoscale features after each successive round will greatly dictate what happens, but the river flooding component is worth monitoring closely.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Wednesday afternoon for IAZ025>028-034>039- 045>050-057>062-070>074-081>084-092>095.