textproduct: Des Moines

KEY MESSAGES

- Shower and storm chances arrive after midnight tonight into Saturday morning over north central into perhaps central Iowa. The overall severe risk is low, but gusty winds are the main potential severe hazard.

- Gusty breezes behind the departing showers and storms Saturday late morning through the afternoon.

- Additional storm chances at times Saturday night into the middle of next week, with peak chances mainly at nighttime.

- Late season heat builds Sunday into next week. Highest temperatures over southern Iowa with heat index values approaching 100 degrees.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 206 PM CDT Fri Aug 28 2026

GOES-East upper level water vapor imagery shows an anti-cylonic spin associated with mid-level high pressure over the Four Corners region with cyclonic spin associated with low pressures over the Ontario/Quebec provinces and the British Columbia province. Within the flow between the British Columbia low and the Four Corners high, a weak shortwave trough will top the ridge and spill across the Dakotas tonight and into the western Great Lakes Saturday. Ahead of this trough, diurnally developed cumulus clouds have developed over Iowa, mainly over east central and southeast Iowa early this afternoon, with filaments of high clouds also drifting overhead along with perhaps a touch of high level smoke. Storms will develop this evening over the Dakotas where there is sufficient instability, shear, and forcing. The 850mb jet of 40 to 45 knots will veer into Iowa late tonight and bring shower and storm chances to northern Iowa and perhaps central Iowa as far south as I-80. Forecast soundings show most unstable instability between 500 and 1000 J/kg with mid-level lapse rates of around 6 C/km with a bit of, but not appreciably large amount, low level dry air. While deep layer shear will be around 40 knots for storm organization and maintenance, the effective shear looks more lacking around 20 knots. Most guidance suggests storms maintaining to some degree into north central Iowa waning as they move into eastern Iowa Saturday morning, though the REFS is a little more aggressive with maintenance. As for severe potential, the hazard of concern is gusty winds. If a cold pool can develop and maintain balance with the system, gusty winds may move into northern Iowa shortly before sunrise through mid-morning Saturday. Convective allowing models are not bullish on this wind potential with the storms, though do show an uptick in winds behind the rain/storms late morning into the afternoon. This appears to be tied to better boundary layer mixing tapping into the winds mentioned above with the waning 850mb low level jet. Winds and gusts were increased several mph above initial National Blend of Models guidance to account for this likely reality. Otherwise, this rainfall will be welcomed as NASA SPoRT's soil moisture in the top 4 and top 16 inches are below the 30th percentile over much of the state with northwestern and north central Iowa below the 2nd percentile - very dry!

Beyond gusty winds through the day Saturday, high temperatures will recover well into the 80s over western and much of central Iowa. The ridge's amplitude will have been flattened by the departing shortwave trough as it shifts eastward and sprawls from the southern Plains into the Southeast by Sunday night. The flattened ridge will keep weak, nebulous shortwaves overhead with the low level jet into Iowa Saturday night into Sunday morning. While instability and shear are less impressive than tonight's values, there may be a few spotty storms that attempt to develop in this time period. Most of this activity wanes by later Sunday morning with capping limiting any further daytime development with highs from the middle 80s over northeastern Iowa to well into the 90s in southwestern Iowa, depending on any residual clouds. SPC does highlight our area with a marginal risk for severe storms into Sunday night. The low level jet is once again pointed into the state with sufficient mid-level lapse rates, deep layer shear, and instability to monitor the severe potential Sunday night.

LONG TERM /MONDAY THROUGH THURSDAY/

Issued at 206 PM CDT Fri Aug 28 2026

Southwesterly flow will remain through at least the first part of next week offering at least low storm chances, which are highest at night, as weak shortwave troughs move through this flow. As the ridge amplifies late in the week, this may aid in pushing the storm track farther away from Iowa. Temperatures will range from the 80s over northern Iowa to the 90s over southern Iowa with dewpoints well into the 60s to low 70s. Heat index values will be well into the 90s to around 103 degrees or so most afternoon hours during next week. Experimental HeatRisk will reach the major/level 3 out of max of 4 to extreme/level 4 of 4 over southern into portions of central Iowa. These high HeatRisk values are being driven by the uncommon late season heat in concert with warm nighttime lows in the 70s with acclimation perhaps an offsetting factor.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1219 PM CDT Fri Aug 28 2026

VFR conditions will prevail for the first half of this TAF period with challenges in the latter half being timing of storm arrival and their impacts. Highest confidence in showers and storms is over northern Iowa at MCW and FOD, where prevailing SHRA and PROB30 TSRA have been introduced. Further restrictions to visibility and ceilings along with moving TSRA to prevailing may be needed in the next cycle or two. There is question on how quickly these showers and storms will dissipate as they move farther into Iowa so just have PROB30 -SHRA at ALO and no mention at DSM or OTM. While the low level jet will be strong, low level wind shear is around 30 knots to have not included any mentions at FOD or MCW. As this showers activity dissipates, winds from the south with gusts of 25 to 30 knots are likely by the end of this valid period into the afternoon.

DMX WATCHES/WARNINGS/ADVISORIES

None.