textproduct: Des Moines

KEY MESSAGES

- Severe storms are expected this evening and overnight through Sunday morning. Large hail and damaging wind are the primary concern. Pockets of heavy rain are also possible.

- Warm and breezy on Sunday with gusts of 35+ mph possible. While a stray thunderstorms is possible Sunday afternoon the main window for thunderstorms will be in the evening and overnight.

- Additional severe storms are expected on Monday with a cold front moving across Iowa. Cooler and dry through the middle of next week.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 338 AM CDT Sat May 16 2026

Late night storms are pushing east of the area early this morning with the surface boundary sinking south and east. Through today theta-e advection into the area will contribute to an increasingly unstable environment. While earlier CAM runs (except the HRRR) remained largely capped through the afternoon, most recent runs have trended towards the HRRR with afternoon development along the pseudo warm front draped across Iowa. Where this boundary will be is uncertain. The HRRR has been consistent with this lifting into central Iowa by initiation around 21z, while the NAM, RAP, and Fv3 are closer to the Iowa-Missouri border. The environment becomes deeply unstable with the HRRR indicating surface based convection to start with 3000+ J/kg SBCAPE and low- and mid- level lapse rates of 7-8 C/km. 0-6 km shear of 30-40 kts will be enough to help organize updates with initial discrete convection. This initial convection will be capable of large hail and damaging wind gusts. Hodographs are curved through the low levels with 200+ m2/s2 of 0-3 km SRH to sustain rotating updrafts. With some low level stretching with will also be a tornado threat with initial discrete convection. Storms may grow upscale along this boundary, resulting in a west-east oriented line of convection. These training storms may create pockets of heavy rain with 2-3" expected based on CAMs and HREF PMM. Isolated heavier totals are possible, with pockets of 5+" hinted at in CAMs. While storms tonight produced around an inch of rain across the area, an additional 2-3" should still be handled well with very dry antecedent conditions. Heavier pockets, especially if they occur in urban areas (urban meaning anywhere in town), could create problems and will need to be monitored tomorrow evening. After 06z an MCS developing across the central plains should push across Iowa through the overnight and Sunday morning. This is more progressive and will help to clear convection out of the area behind it. Strong winds are possible with the MCS, however by the time it reaches the area it should be trending down with the LLJ nosing into southern Iowa helping to sustain it.

After early morning storms taper off much of Sunday should be dry as soundings indicate a stout cap in place. It will be breezy with dry low level allowing for mixing with 30-40 kts through the mixing layer. While the higher end gusts may not be realized, 35-40 mph winds at the surface are certainly possible. The wildcard on Sunday, as has been mentioned in previous discussions, is how any outflow boundary put out from morning convection will impact the strength of the cap. There is certainly plenty of instability there should anything be able to break that cap. Current trends suggest that convection will hold off until the low level jet increases with initiation in eastern Nebraska in the early evening with that activity growing upscale and moving into the area through Sunday night into Monday morning. Damaging winds should be the primary risk as the complex moves into Iowa Sunday night, though far western portions of the area may see a window for hail and perhaps a tornado as the complex is growing upscale.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 301 PM CDT Fri May 15 2026

Monday will dawn with storms either lingering over some portion of eastern Iowa as a result of storms that push across Iowa Sunday night. As these depart, the stronger synoptic scale forcing will be moving closer to central Iowa through the day along with a surface cold front. The forcing should be more than sufficient for storm development and severe storms are likely given the strong instability and shear parameter space. While four days away, the most likely timing will be from mid-afternoon into the evening hours before the front likely pushes the storms out of our forecast area by Tuesday morning. In addition to the severe storm concerns, there is a slight risk of excessive rainfall on Monday. Given successive rounds of rainfall, will have to see if certain areas receive repeat rainfall and become more susceptible to flash flooding. Of course, urban areas will be in play in any event if rainfall of 2 to 3 inches occurs in just an hour or two. This risk was highlighted in the 6z run of the experimental WPC Urban Rain Rate Dashboard for Des Moines with a 5% chance of reaching the 5 year return interval. Will need to keep an eye on rivers; however, many are near base flows so there is capacity along with soils expected to take the first round to perhaps two rounds of rainfall. This is shown in the 5 day National Water Model (NWM) forced by the GFS that generally shows high annual exceedance probabilities (AEP), though tributaries in both the Thompson and Chariton basins shows 10% AEPs/higher flows.

With the cold front clearing the area by early Tuesday, cooler and drier conditions are then forecasted through Wednesday and perhaps Thursday as surface high pressure moves across the region.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 638 AM CDT Sat May 16 2026

Isolated fog has developed this morning in northern Iowa in the wake of the overnight thunderstorms. This is expected to dissipate quickly this morning, but until then KMCW and reaching to KFOD could see brief periods of 1/4SM FG. Thunderstorms develop just before 00z in central and southern Iowa, starting scattered and then becoming more widespread through the evening. A progressive line of storms will then move in from west to east through the overnight with storms ending at or just beyond the current TAF period. Storms may be severe, producing strong wind gusts and large hail, in addition to pockets of heavy rain. There is uncertainty in the northern extent of coverage so have kept from KMCW at this time. Further refinements of storm timing are expected in later updates.

DMX WATCHES/WARNINGS/ADVISORIES

None.