textproduct: Des Moines

KEY MESSAGES

- The heavy rainfall threat for Iowa continues due to ongoing convection with efficient rainfall production, and further still by convection expected tomorrow.

- Severe weather is possible tomorrow, with damaging wind gusts and heavy rain as the primary threats. Large hail and a tornado or two are also possible.

- The pattern remains active with storm chances through the weekend and mid next week.

SHORT TERM /THROUGH SATURDAY/

Issued at 325 AM CDT Fri Aug 14 2026

Convection is ongoing across central Iowa which the HRRR has been struggling to assimilate over the past several hours (up to 06z/1am Friday). The Friday 00z suite of CAMs has the basic footprint down for the ongoing convection, however, they have been struggling with timing for convection. One potential reason for this is that CAMs are not properly modeling the Elevated Mixed Layer (EML). Model soundings suggest decent capping up to around 700mb. Looking at mesoanalysis, these storms are forming in an area with decent deep moisture convergence. The expectation through the night is that these storms will continue to develop and push to the north/northeast into the mid to late morning hours. Models show the low level jet weakening around 12z/7am, which would lead to any remaining convection decaying as it loses its forcing. Until that happens, the ongoing convection will have fairly high rain rates, as they are not moving particularly quickly. SO far, these storms have already produced over 1in of rainfall in an hour, with one swath of just over 2in in an hour. Unseasonably high dewpoints and PWAT values exceeding 2in aid to the heavy rainfall potential, however, with convection being elevated updrafts would not be as deep to take advantage of the whole warm cloud layer (around 13500ft).

Due to the poor representation of ongoing convection, more uncertainties crop up as we move through the day today, where the bulk of our heavy rain potential lies. In central Nebraska, an MCS driven by a shortwave is in the process of decaying. As it decays, an associated MCV will move towards Iowa which will serve as the focus point for the next round of storms. There is some severe potential with convection in the afternoon, given decent shear (25- 35kts) and a strong push of instability into Iowa. Damaging winds looks to be the primary threat, with large hail and a tornado or two possible. See SWODY1 for details. The uncertainties are with the location of the MCV and how convection behaves as it forms. The most likely scenario is cells that quickly grow upscale before moving east along the instability gradient that sets up, which looks to mainly be south of the Highway 20 corridor. The northward or southward extent of this line will have implications on which areas receive the most rainfall. As mentioned before, PWAT values are quite high and there is another push of moisture through the day. This, combined with warm cloud depths will lead to efficient rainfall production.

As the MCS exits the area, the rest of tonight looks to be fairly dry. Most of the day tomorrow will be fairly dry before more shower and thunderstorm chances return Saturday night into Sunday morning.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Issued at 252 PM CDT Thu Aug 13 2026

The ring of fire pattern continues through Saturday night. PWATs over 2" linger until a cold front sweeps through Sunday morning. GEFS/EPS guidance highlights Saturday into Sunday morning as another period of storm chances, with similar potential for marginal severe chances and flash flooding as we have seen most of this week. High pressure and drier canadian air may bring a brief break from any rain chances before the ridge breaks down a bit and shortwaves and enhanced flow return to our part of Midwest by midweek. This will need to be monitored for renewed severe weather and heavy rain concerns.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 544 AM CDT Fri Aug 14 2026

Prevailing IFR to MVFR conditions are expected through this TAF period. Showers and thunderstorms are lifting north across Iowa this morning and are currently impacting KDSM and KOTM. As thunderstorms lift north, terminals across northern Iowa could see impacts from this activity, although storms should weaken through the morning. Otherwise, lower ceilings will linger through the morning before recovering slightly pending another round of showers and thunderstorms beginning around 20z. Depending on how quickly the next round of storms clears the area, fog will be possible overnight Friday into Saturday morning. Due to low confidence in storm timing, the only mention of fog is at KDSM.

HYDROLOGY

Issued at 326 AM CDT Thu Aug 13 2026

Periods of heavy rainfall remain possible through tonight. Cumulative impacts from several rounds of moderate to heavy rainfall beginning Thursday morning and another round currently ongoing across central Iowa followed by more storms later today and tonight. These may lead to river and/or flash flooding and certainly will lead to significant ponding.

WPC has carried the previous Day 2 excessive rainfall outlook (ERO) to moderate risk for Today into the Day 1 outlook and includes much of central and southern Iowa. The primary concern with the current convection is it is moving across areas that received 2-4 inches of rainfall less than 24 hrs ago. In addition, this heavy rain may move into the Des Moines metro and lead to urban impacts. Will also be monitoring Walnut Creek, which responded to the previous rainfall and reach action stage. Additional heavy rainfall will increase the potential for flooding along these faster responding streams including Walnut Creek.

Little change regarding the potential for river flooding, as significant within-bank rises are still expected on many streams. At least isolated to scattered minor river flooding is possible, with more significant flooding possible as well. Since QPF will be around rainfall-runoff inflection point, just a little more QPF than forecast may produce more significant flooding. For example, if QPF averages around 0.5 to 1 inch more than forecast, then widespread minor river flooding with multiple locations seeing moderate or possibly major flooding may occur.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Saturday morning for IAZ023>028-033>039- 044>050-057>062-070>075-081>086-092>097.