textproduct: Des Moines

KEY MESSAGES

- Hot and humid this afternoon with highs pushing into the 90s and heat indicies near 100F.

- Another chance for severe storms possible Tonight into early Wednesday morning. A Marginal Risk issued (Level 1 of 5) with damaging winds the primary concern.

- Another round of storms expected Wednesday night into Thursday. Locally heavy rainfall possible.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 253 PM CDT Tue Aug 11 2026

Our County Warning Area (CWA) missed the main convective event by one county this morning, as the primary wind threat developed just east of Waterloo and tracked into eastern Iowa. Dry conditions will persist this afternoon, with highs climbing into the 80s and 90s across central Iowa. Given the lack of morning convection across southern Iowa, enhanced diurnal heating combined with mid level dry air and deeper boundary layer mixing, highs could climb into the mid 90s across southern Iowa during peak heating hours. Dew points in the upper 60s and lower 70s may briefly push heat index values into the lower triple digits in isolated spots; however, no heat headlines are anticipated due to low confidence in widespread 105 heat indicies. Similar to yesterday, robust afternoon instability will be present across the area. A few CAMS attempt to develop isolated storms, but most guidance maintains a strong 13-15C cap that should suppress initiation. This area will continue to be monitored through the afternoon.

Tuesday night

Attention shifts to Tonight for another potential severe storm threat. Similar to Monday, the scenario remains highly dependent on upstream evolution and whether key ingredients overlap. Initial supercellular development is expected across northern Nebraska and the southern Dakotas Tuesday afternoon. As these storms mature and generate strong cold pools, upscale growth into a MCS is expected. However, uncertainty remains regarding the track and longevity of the MCS. Model guidance depicts 2500 to 3500 J/kg of MLCAPE extending into central Iowa late tonight into Wednesday morning. However, synoptic forcing across the local area appears relatively weak, meaning storms will require additional mesoscale lift to tap into elevated instability. Furthermore, several models indicate mid- level dry air as convection approaches, which could cause storms to decay without sufficient forcing. Ultimately, storm evolution hinges on the positioning and strength of the LLJ. High Resolution guidance (HRRR,NAM and RAP) maintains the LLJ axis further south across southern Iowa, keeping it detached from the primary storm track. Conversely, the RRFS and GFS has the axis further north, allowing the MCS to latch onto better forcing. IF this northern solution materializes, the risk for severe weather increases, with damaging wind gusts being the primary concern. The highlight the severe potential the Storm Prediction Center has placed most of Iowa in a Marginal Risk (Level 1 of 5).

Wednesday

Any lingering morning convection should exit the CWA by late morning, giving way to another warm and humid day. Highs will range from the upper 80s to lower 90s. Factoring in the humidity, heat indices will climb into the mid to upper 90s, with a few spots approaching the triple digits. Attention then turns to a weak surface boundary progged to stall across southern Iowa by Wednesday afternoon. While a few CAMS attempt to initiate convection along this boundary, modest CIN will likely suppress widespread development, keeping confidence low. However, this bears watching; forecast soundings depict dry low level air, suggesting a localized severe threat if any sustained updrafts can break the cap.

Wednesday Night

Precipitation chances increases significantly Wednesday night into Thursday. An upper-level shortwave originating over the Rockies will eject eastward across the Plains. Ahead of this feature, a strengthening LLJ will advect a surge of moisture into the region, pushing surface dew points well into the 70s by early Thursday morning. As highlighted in the previous discussion, PWATs will pool near 2" across the CWA. The high moisture profiles will support highly efficient rainfall rates as storms move into central Iowa. A localized flash flooding threat will exist.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 249 PM CDT Tue Aug 11 2026

Active weather persists into Thursday night as another shortwave traverse into the Plains, The SPC currently highlights the southern CWA in a Marginal Risk (Level 1 of 5) for Thursday. The active pattern remains in place through Saturday, maintaining low-end severe storm probabilities. A more robust cold front will finally sweep through the region on Sunday, bringing a cooler and drier airmass. Highs look to top out in the upper 70s in northern Iowa to lower 80s in southern Iowa.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 101 PM CDT Tue Aug 11 2026

VFR conditions to prevail through the end of this TAF period though there is some uncertainty near the latter half of the period. Satellite imagery shows mostly clear skies across much of Iowa, though remnant cloudiness from departing showers lingers over far southeast sections. There is low confidence regarding overnight shower and thunderstorm development across central Iowa. Should convection materialize operational impacts are possible at KFOD,KDSM,KALO and KOTM; PROB30 groups have in introduced to reflect this potential.

DMX WATCHES/WARNINGS/ADVISORIES

None.