textproduct: Des Moines

KEY MESSAGES

- Storms are expected particularly across the central part of the state this evening through the overnight and again tomorrow afternoon into Saturday morning.

- Storms that occur tonight and tomorrow pose a threat for large hail and damaging wind, and perhaps an isolated tornado. The larger impact will be large rainfall amounts. There is a Flood Watch issued for most of the state for potential for flash flooding in urban areas as well as stream and river flooding.

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

SHORT TERM /THROUGH SATURDAY/

Issued at 252 PM CDT Thu Aug 13 2026

Lingering subsevere storms and anvil shield are in the process of clearing the CWA this afternoon as the morning MCS has dissipated and moved east. Our active weather pattern continues on through the short term with a ridge over the south central US and ridge-riding shortwaves continuing to be directed across Iowa. The outflow boundary was pushed into Missouri this morning but has begun recovering instability into southern Iowa. A conditional storm threat exists towards southern to central Iowa along the instability gradient. If surface based convection can develop on this boundary before dark, it will be in an environment with decent low level shear given surface easterlies. This could support a brief window for supercells, however, any surface based convection will be opposing poor low level lapse rates and subsidence.

Because the low has developed eastward, the main storm development region tonight will be focused more over Iowa rather than development over the high plains and MCS maturing off to our west like has been the case the last several nights. The next round of storms tonight may be less organized and will be primarily driven by the LLJ exit region convergence. Convection is expected to develop generally after 2z tonight on the gradient of better lapse rates and MUCAPE. Instability should certainly be sufficient for support widespread convection, though shear will be limited above 3km. 1-3km shear on the order of 30-40 knots may be favorable for some brief bowing segments, but this effect may be offset by largely saturated profiles and limited DCAPE, so cold pools may struggle to get organized. All things considered the threat still remains for some large hail or damaging winds. The larger impact will likely be rainfall amounts and hydrology impacts, so see the updated hydrology section below. A swath of 1-3" will be common especially where continued storm development occurs around the LLJ nose.

By Friday morning, rain clears out in the morning once again and reloads for an afternoon and evening round of storms. An MCV rides the western fringe of the ridge and will provide the forcing needed for afternoon storm development. A weak surface low associated with the MCV meanders across the central part of the state through the afternoon and evening. Beginning with afternoon severe threats. CAMs are notoriously bad at handling the low level wind fields in these types of environments. Mid and upper level flow will be weak, so long duration storms are less likely. However, the strengthening LLJ through the afternoon could lead to some enhanced low level shear. The most likely environment tomorrow is one with some pockets of enhanced CAPE and perhaps 0-3 CAPE, overlapping with mainly some low level shear. This could support some transient supercell or bowing segments for some isolated large hail and gusty winds with perhaps a tornado if everything comes together. Again the larger impact will be hydro concerns. Weak flow and PWATS over 2" will result in slow moving or training storms with efficient rainfall production through a large portion of the Friday overnight period. HREF guidance shows widespread 1-3" of rain through Friday night with the main swath setting up over central to eastern Iowa. However, a few members show precip amounts over 5 inches over some very localized areas. Again, CAMs frequently don't handle convective coverage well from MCV setups so there is still large uncertainty in rain totals tomorrow.

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 1038 PM CDT Thu Aug 13 2026

Storms lifting northward out of Kansas, along with additional t-storm development associated with the low level jet, will begin to impact the KDSM/KOTM terminals after 08Z tonight. Storms will then continue to lift n/newd and impact KFOD/KALO and possibly KMCW between Expect decreasing CIGs to MVFR to IFR, with occasional lower VSBYs with heavier thunderstorms. After the initial round of storms, persistent MVFR to IFR may linger through the day, especially in the north through the afternoon. There is a chance for additional thunderstorm development tomorrow afternoon and into tomorrow tonight.

HYDROLOGY

Issued at 252 PM CDT Thu Aug 13 2026

Active weather with periods of moderate to heavy rain are expected through at least Friday night. Main questions are location and amounts, which may significantly impact hydrologic responses.

WPC plans to upgrade their Day 2 excessive rainfall outlook (ERO) to moderate risk for much of our CWA south of US Hwy 20. A Day 2 moderate risk ERO is rare for our area, averaging once every 2+ years, which highlights the potential significance. Locally significant flash flooding is possible in urban areas or other areas that receive the heaviest rain. We typically have decent capacity this time of year for heavy rainfall in the rural areas, however, the recent bouts of moderate to heavy rain have reduced that capacity. Additional heavy rain especially with current QPF values would produce more significant responses than typical.

In terms of river flooding, significant within-bank rises are 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.