textproduct: Des Moines

KEY MESSAGES

- Hot and humid through the weekend with heat peaking on Monday.

- Scattered thunderstorms across southern Iowa this afternoon and evening. The severe potential is very low.

- More widespread thunderstorms are expected on Monday. Strong to severe storms are possible.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 255 AM CDT Sat Jul 18 2026

High pressure centered south of the state has kept skies clear across most of Iowa through the overnight with very light wind. Meanwhile, the trough across the Great Lakes region has deepened with a boundary trailing across Wisconsin and into Minnesota. Thunderstorms have developed along this boundary overnight and continue early this morning as it sinks into northern Iowa. Convection is expected to largely pass east of the area nearer the better forcing and diminish with sunrise, though an isolated thunderstorm may clip northeast parts of the area early this morning. That trailing front will continue to sink across Iowa through today. Northern Iowa will see the most notable effects, as the boundary pushes south early enough to impact day time highs. Temperatures there will top out in the mid 80s. Central and southern Iowa will be delayed such that temperatures will warm through the low 90s yet today. With dewpoints in the low 70s south of the boundary, heat indicies in central to southern Iowa will near 100 this afternoon. The boundary reaches southern Iowa late afternoon into the evening. Thunderstorms are expected to redevelop along the front which will likely be along and south of the I-80 corridor. There will be 1500+ J/kg of MLCAPE available for storm development, but very little (<15 kts) effective shear to organize convection. As such, storms are expected to be short lived and sub-severe.

On Sunday the thermal ridge rebuilds and shoves the boundary off to the north and east with temperatures into the low 90s again for much of the area. Isolated thunderstorms are possible in the afternoon along this remnant boundary, however forcing is quite weak and any development is expected to be rather isolated in nature should it occur. Zooming out, a shortwaves moving across Canada will reach the upper midwest and the Great Lakes trough late Sunday. This interaction will result in a couple local impacts. First, the trajectory of upper level flow will shift such that smoke that was sweeping east may filter into parts of northern and eastern Iowa on Sunday. This trough will also bring better forcing to the area with a strong upper level jet now overhead later Sunday and on Monday. With the troughing north and east and thermal ridge to the west, a notable gradient in instability looks to set up across Iowa along which storms are expected to develop and follow on Monday. With better shear (40+ kts at 0-6 km) for storm organization and more than sufficient instability (2000-2500+ J/kg MLCAPE), severe storms are possible.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 225 PM CDT Fri Jul 17 2026

The long-term forecast has much more uncertainty. For Monday, deterministic models are hinting at more thunderstorm potential with our biggest consideration being the location of the ridge. The eastern extent of the ridge's influence will determine the axis of where any organized convection would track. The most notable takeaways as far as storm potential Monday is that the ingredients are in place and better forcing will be available as we have a pattern change taking place. As we transition to northwesterly flow, subtle shortwaves will ripple overhead which will drive any precipitation chances through the next week. LREF and deterministic guidance show that the ridge will be well clear of Iowa through midweek, which would lead to an increased area of potential coverage for showers and thunderstorms as opportunities arise. Finally, with this pattern chance, temperatures are going to trend cooler. Instead of making daily runs for the 90s, temperatures will be in the lower to mid 80s at points through the week.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 641 AM CDT Sat Jul 18 2026

A few scattered thunderstorms have developed near KMCW that will be south of the terminal by 12z. A front will sink south across Iowa today with winds shifting to out of the north behind it, then northeast by this evening. Scattered thunderstorms will redevelop on the front in central and southern Iowa this afternoon and evening. Have included prob30 mention of -TSRA at KOTM where impacts are most likely. A stray storm may reach near KDSM, however confidence is lower here and have not included in the TAF at this time.

DMX WATCHES/WARNINGS/ADVISORIES

None.