textproduct: Des Moines

KEY MESSAGES

- Early showers will continue to fade as they head east leaving a dry afternoon.

- Isolated severe storms are possible with a passing cold front, though dry air may limit coverage.

-A more active weather pattern will return with additional thunderstorm chances next weekend, but any further details remain unclear at this range.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 312 AM CDT Mon Aug 24 2026

Monday

Monday morning will begin with a slight increase in cloud cover compared to Sunday, alongside a localized light fog that will yield minimal operational impacts. Recent mesoscale analysis reveals a strengthening LLJ positioned over north-central Nebraska and south- central South Dakota. Along the nose of this LLJ axis, where richer low level moisture return is concentrated, showers and thunderstorms have begun to initiate. Overnight, the LLJ and associated convection will shift gradually eastward. Areas near and west of Omaha and Sioux Falls will maintain 30-50% PoPs through the morning hours. As showers propagate eastward into central Iowa, they will increasingly decouple from the primary moisture transport axis and encounter a significantly drier airmass. Consequently, precipitation will diminish rapidly, with the highest remaining chances (~30%) confined to Crawford and Sac counties. PoPs drop to near 10% toward Des Moines, where any surviving activity will be limited to trace amounts of light sprinkles.

By Monday afternoon and evening, deep layer mixing and dry air entrainment will continue to scavenge lingering morning moisture, yielding dry surface conditions. Synoptically, a 500 mb trough currently centered over the Great Lakes will slide eastward, clearing the way for a shortwave to approach the region by Wednesday morning. Further west, a shortwave traversing the Pacific Northwest and southern British Columbia will ride along the upper level ridge, carving out a surface trough across the Northern Plains and Upper Midwest. An associated cold front is projected to cross the Plains and Midwest Tuesday morning into the afternoon.

Tuesday

Isolated showers and storms remain possible across northern Iowa Tuesday morning, though the most favorable forcing will reside over southern Minnesota along the LLJ axis. Heading into Tuesday afternoon diurnal destabilization will increase; however, forecast soundings indicate a notable thermal cap that could suppress convection. Where storms manage to initiate, 30-35 0-6 km bulk shear will be sufficient to support isolated strong to severe storms. The Storm Prediction Center has places portions of northwest and Central Iowa in a Marginal Risk (Level 1 of 5), with damaging wind gusts and large hail as the primary hazards.

A key forecasting challenge remains moisture availability across central Iowa. Forecast soundings depict a prominent dry slot in the mid levels. Furthermore, upstream convective development across central and northwest Nebraska could effectively rob low level moisture transport into the local area. Given these uncertainties over the next 36 hours, updates to the convective risk profile may be necessary as high resolution guidance arrives. Following the cold front passage Tuesday night, quiet and dry conditions will return Wednesday.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 108 PM CDT Sun Aug 23 2026

By Wednesday the large 500 MB heat dome will remain in place over the southwestern/south central CONUS, while the trough described in the SHORT TERM section above moves away to our east. This will allow deep-layer ridging to reassert itself just to our west, leading to a period of dry, quiet, and seasonally mild weather with daily highs in the low to mid-80s for the remainder of the week. By Friday and Saturday the pattern will begin to shift a bit, as two large 500 MB lows develop over Canada and shunt the ridge southward, with the heat dome retrograding more over the far southwestern CONUS near Arizona and New Mexico. This will cause 500 MB flow over Iowa to become more zonal, with multiple shortwave impulses moving through the flow and providing several opportunities for thunderstorms from Friday or Saturday into early the following week. While the details of any such storms are very uncertain at this range, it is fair to say that overall the weather pattern will be more active by next weekend.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 639 AM CDT Mon Aug 24 2026

VFR conditions to prevail through the end of this TAF period. Light rain showers are passing thorugh central Iowa this morning with a scattered clouds present around 5,000 ft. Showers should taper off over the next few hours. Scattered clouds between 5000 and 7000 feet will continue into the afternoon before things clear out tonight.

DMX WATCHES/WARNINGS/ADVISORIES

None.