textproduct: Des Moines

KEY MESSAGES

- Thunderstorms with pockets of heavy rainfall will move through the area this morning.

- Severe thunderstorms and excessive rainfall are possible this 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 TUESDAY/

Issued at 323 AM CDT Mon Sep 14 2026

Overnight surface analysis shows high pressure anchored over the western Great Lakes. While the high maintains influence over much of the region, the next system is rapidly advancing northeastward, as evidenced by expanding radar returns across Nebraska and Kansas. Surface observations place the approaching warm front in southwestern Missouri, extending northwestward through Kansas into central Nebraska. Locally, the area remains in the pre-warm frontal environment, with temperatures ranging from the lower 50s in the northeast to the lower 60s in the southwest.

EARLY MORNING THROUGH THIS EVENING:

A warm front will lift northeastward through the region today, bringing an initial round of showers and thunderstorms this morning. A lull in activity is expected as the area transitions into the warm sector. Thermal destabilization may take place this afternoon, supporting the potential for strong to severe thunderstorms through the early overnight hours but once the severe threat wanes, a hydrologic threat emerges as rounds of thunderstorms with potential training overnight.

At this time yesterday, guidance depicted an upper-level trough traversing the northern Rockies into the High Plains of eastern Wyoming and the Dakotas. Overnight model runs maintain this upper- level trough but displace it further north, with an embedded closed circulation tracking northeastward across Montana toward the lakes of Manitoba. As this feature advances, the associated warm front will lift northeastward through the forecast area this morning. The initial convective line over Kansas and Nebraska continues to track northeastward toward Iowa. Forecast soundings ahead of this line are not particularly impressive, but morning activity is being sustained by an LLJ that is intensifying ahead of the cold front. Nonetheless, strong embedded convection capable of producing heavy rainfall remains possible within this initial morning push.

Behind the warm front, the region will be positioned within the warm sector, where the LLJ will strengthen further this afternoon. Kinematic parameter space will be fully supportive of strong to severe convection; however, the severe threat remains conditional due to potential instability deficits and widespread mid-level capping. Should boundary-layer mixing erode the cap, severe thunderstorms are forecast to develop and move northeastward across southwestern Iowa during the afternoon and evening. Overnight CAMs suggest a few discrete supercells could grow upscale into a convective complex by the early evening. Kinematic fields, specifically vertical wind shear and SRH, are favorable, but surface- based convection will depend on complete capping erosion or elevated storm initiation. Should severe storms develop, all hazards are likely. Outside of the convective threat, widespread gusty winds are expected within the warm sector. While a low-level inversion will keep the strongest winds aloft, surface gusts to 30 mph are likely, with higher gusts possible where deeper mixing occurs.

Alongside the severe weather threat, a widespread heavy rainfall and flash flooding hazard exists for this afternoon and evening. Pockets of heavy rain will accompany the morning convection; however, as the LLJ intensifies and drives robust moisture advection, the flash flooding potential will increase substantially. Forecast soundings depict PW values increasing from 1.50 inches to over 2.00 inches overnight, paired with tall, skinny CAPE profiles and mean mid-level flow oriented parallel to the surface boundary, favoring training convective cells. Deterministic models and ensembles consistently highlight southwestern portions of the forecast area for the highest flash flood risk and greatest QPF totals. The deterministic NAM and high-resolution CAMs indicate widespread 2 to 4 inch rainfall totals, with ensemble guidance showing similar or locally higher amounts. Given these factors, a collaborated WPC Day 1 Moderate Risk for excessive rainfall was introduced overnight, alongside a Flash Flood Watch issued during the evening shift for these same locations.

TUESDAY:

The cold front will push through the area Monday night into Tuesday, but it is forecast to stall near the region, serving as the primary focus for additional rounds of showers and thunderstorms throughout Tuesday. While severe weather is not anticipated, frontal forcing will again support heavy rainfall. Deterministic soundings maintain a highly efficient rainfall profile similar to Monday, with PW values hovering between 1.50 and 1.70 inches, which is above the 90th percentile, and saturation extending up to 200 mb alongside weak, deep CAPE profiles. Model guidance exhibits run-to-run variability regarding the exact placement of the heavy rain axis, but consensus favors locations along and south of the Interstate 80 corridor. This zone is highlighted within a WPC Slight Risk for excessive rainfall, and given antecedent soil saturation from Mondays precipitation, an extension of the Flash Flood Watch will likely be required.

A dynamic weather system will affect the region from Monday through Tuesday, bringing consecutive threats of severe weather and heavy rainfall. A warm front lifting through the area this morning will bring initial showers and embedded storms, followed by a warm sector transition where severe thunderstorms and high surface wind gusts become possible by late afternoon if atmospheric capping erodes. As an associated cold front approaches and stalls across the region Monday night into Tuesday, rich atmospheric moisture and cell training will create a significant flash flooding threat overnight, particularly across southwestern Iowa and along the Interstate 80 corridor. The heavy rain and flash flooding threats will continue into Tuesday.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

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 /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 637 AM CDT Mon Sep 14 2026

A line of showers and thunderstorms will move through the area this morning. Categorical reductions are likely with this line; as well as, gusty and erratic thunderstorm winds. Once this line moves off to the northeast, a lull in activity is expected through the afternoon where gusty south to southwest winds are expected to develop. Widespread wind gusts from 25 to 30 knots will possible. By this afternoon and evening, shower and thunderstorm chances will increase again and persist through the remainder of the TAF period. Gusty and erratic thunderstorm winds and category reduction will once again be likely with the second round of showers and thunderstorms.

HYDROLOGY

Issued at 240 PM CDT Sun Sep 13 2026

Multiple rounds of persistent and potentially heavy rainfall begin today as a warm front lifts northeast through the region this morning. This initial round of showers and thunderstorms should be progressive enough but ponding of water and isolated instances of flash flooding still remain possible with this first round. Following a lull in activity later this afternoon, a cold front will move into the region later this evening bringing heavy rain through much of the overnight. Driven by a strong LLJ, convergence along the front and potential training the flash flooding potential will increase substantially. Forecast soundings depict PW values increasing from 1.50 inches to over 2.00 inches overnight due to robust moisture advection, paired with tall, skinny CAPE profiles and mean mid-level flow oriented parallel to the surface boundary, favoring training convective cells. This combination has prompted the issuance of a Flash Flood Watch and WPC Day 1 Moderate Risk for excessive rainfall.

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

Flood Watch through Tuesday morning for IAZ025>028-034>039- 045>050-057>061-070>073-081>083-092-093.