textproduct: Des Moines

KEY MESSAGES

- Thunderstorms are expected mainly across southern Iowa this afternoon and evening. A few strong to severe storms are possible along with isolated pockets of heavy rain.

- Additional scattered thunderstorms are possible overnight Thursday through Friday morning in northern Iowa.

SHORT TERM /THROUGH FRIDAY/

Issued at 222 PM CDT Wed Aug 19 2026

A complex of thunderstorms has pushed across Nebraska through the day, reaching eastern Nebraska to far western Iowa by 2pm. These are expected to continue on a southeast to east-southeast trajectory following the mean wind and moving across southern Iowa. At the same time a weak boundary is draped across southern Iowa, fed by weak moisture transport into the area and convection has begun to bubble along this boundary this afternoon. This area has 2000 J/kg of MLCAPE along with 40 kts of 0-6 km shear as noted by the SPC mesoanalysis page. Much of this shear is in the mid to upper portions of the soundings and should sustain updrafts for hail growth. For strongest cores, severe storms producing large hail is possible, along with a few severe wind gusts. Low level instability is on the rise in southern Iowa with 100-150+ J/kg of 0-3 km CAPE and funnel clouds are possible with low level stretching. A few have already been spotted in southern Nebraska this afternoon. As storms move across southern Iowa a few pockets of heavy rain are also possible. PWATs are around 1.5" so widespread heavy rain is not anticipated, but a few pockets of heavier rain with ponding is certainly possible.

The surface high across Minnesota into northern Iowa will continue to sink south overnight and on Thursday. A few pockets of patchy fog will be possible on Thursday morning with clearing skies and light wind. The high pressure across the area will help to keep the area dry for most of the day on Thursday. Late Thursday an upper level embedded shortwave with associated surface low will pass across the upper midwest. Storms across South Dakota and Minnesota are expected to diminish in strength when they swing into northern Iowa on a trailing boundary late Thursday night through Friday morning. The severe risk is expected to diminish quickly beyond northwest Iowa as storms become elevated with modest instability and mid level lapse rates.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 222 PM CDT Wed Aug 19 2026

The ridge-trough pattern across the CONUS will continue to amplify as we head into the weekend, with Iowa continuing to be positioned on the interface of the two, under enhanced NW flow. A similar pattern appears to be in place into early next week as well. There is still significant uncertainty timing of the frontal passage Friday, with the NAM even suggesting it holds off until Friday evening. NAM/GFS/ECMWF all suggest some storm chances Friday night, though more focused to our west under better instability. These storms would have a moderate amount of instability and bulk shear overlap and could perhaps pose a severe threat, hence the marginal across our area and slight risk to our west. GFS/ECMWF suggest the next shortwave (or waves) passing through the enhanced flow sometime Saturday night through Sunday, though timing still varies. With the passage of the cold front on Friday, and replacement with high pressure through the weekend, gulf moisture flow seems unlikely. However, evapotranspiration is still significant and may provide enough moisture for some marginal instability and low end storm chances. All things considered, the weekend seems drier overall, with a few marginal storm chances with uncertain timing. Temperatures remain relatively unchanged from this past week, with highs in the upper 70s and low 80s. More significant instability appears to return early next week, ahead of another cold frontal passage according to deterministic models. There is still uncertainty in timing of that front, and any further details given by deterministic models at this stage are certain to change.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1044 PM CDT Wed Aug 19 2026

VFR conditions prevail over the area late this evening, but will see the potential for visibility reductions as patchy fog develops through the morning. The greatest fog potential will be over southern and western Iowa, with KFOD and KDSM on the fringes of these chances. Therefore, have added 6SM BR for both these sites and will amend as conditions evolve. KOTM will have a better chance for fog, especially with recent rainfall and clouds clearing out of the area, so have went with a few hours of 5SM visibilities. Cnoditions improve at all sites shortly after sunrise, with light winds and mostly clear skies on Thursday. There is a low potential for isolated showers/thunderstorms near KMCW and KALO tomorrow evening, but no mention in TAFs at this time.

DMX WATCHES/WARNINGS/ADVISORIES

None.