textproduct: Des Moines

KEY MESSAGES

- Thunderstorms will move across northern Iowa this morning, and perhaps reach central and even southern Iowa by midday before fading out in the afternoon. There is a low risk of severe weather in the early morning, mainly across northern Iowa, in the form of isolated hail and wind gusts.

- After the storms, breezy and gusty conditions will develop across most of the area late this morning and through the afternoon.

- Notably warmer weather will build in by Sunday and into next week. Heat Index values may near 100 degrees at times, mainly across the southern half of Iowa.

- Additional storm chances return at times into the middle of next week, with peak chances falling mainly from the overnight into early morning hours.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 205 AM CDT Sat Aug 29 2026

As anticipated, a 500 MB shortwave trough is overtopping the larger-scale ridge over the High Plains at this hour, generating clusters of thunderstorms moving from eastern South Dakota into southwestern Minnesota. Short-range model guidance and radar trends support these storms continuing to progress east southeastward into the northwestern counties in our forecast area before sunrise, then into at least the northern half of our area later this morning before diminishing and departing to the northeast around midday or early afternoon. There is some question as to how far south the rain will reach before washing out, but chances along the I-80 corridor have increased (~40% POPs) and it is possible they may even make it a bit farther southward than that. Have also increased POPs to 100% in our northern/northeastern counties this morning, but while confidence in rain and storms occurring in that area is very high, confidence in intensity and any severe weather potential is somewhat lower. Currently, a nocturnal low-level jet around 850 MB extends from eastern Nebraska up into southeastern South Dakota, with the enhanced storms sustaining themselves along the nose of the jet. There is a reservoir of modest instability (MUCAPE of 500-1000 J/kg) and seasonally strong effective bulk shear (40-50 KT) supporting strong updrafts. However, the storms have remained elevated thus far with no organized cold pool developing as of this writing, and no severe weather has been reported in that area as of yet. Further, the instability and shear parameters are much weaker in our forecast area, and are expected to remain so, or at least until the storms have already moved in (i.e., outrunning their better instability/shear). This would support a weakening trend in the convection as it approaches and enters our area, however, the low-level jet will also pivot and point more across our area later this morning, which may provide enough impetus for a low-end severe weather threat. Isolated hail may be possible, mainly in our northern counties, along with the potential for strong winds *if* a cold pool can sufficiently organize. Overall, the severe weather threat will be marginal as outlined in SPC products.

The aforementioned 850 MB jet will orient from southwest to northeast directly across central Iowa by around midday today, and remain there through the weekend. Later this morning and afternoon, as low-level mixing increases with diurnal heating, downward momentum transfer will result in breezy conditions and the current forecast calls for winds of 15 to 25 MPH with some gusts to around 35 MPH. This may also aid warming today as warmer temperatures aloft move overhead, however, it also remains to be seen how much convective cloud debris or surface cold pool remnants may mitigate this warming, especially in our northeastern counties where the latter effects are more likely to occur. Considering these competing factors, have continued the trend of increasing wind speeds/gusts today, and maintained high temperatures pushing 90 degrees in our southwestern counties, but nudged high temperatures down just a bit into the lower 80s in our northeastern counties where more substantial warming will likely wait until tomorrow. Also maintained a dry forecast for tonight, with deep-layer ridging building overhead, the nose of the low-level jet staying well to our northeast, and no discernible forcing mechanism evident.

The 500 MB heat dome that has been present over the southwestern U.S. for many days now will finally begin to slide eastward this weekend, and by Sunday morning should be centered somewhere around eastern Oklahoma. Meanwhile, a 500 MB trough will move over the northwestern U.S. and southwestern Canada, with the steering flow between these two systems pivoting around to more west southwesterly over Iowa and the Midwestern states. In response, a broad surface low pressure trough will remain nearly stationary in a southwest-to-northeast orientation from southwestern Kansas up across eastern Nebraska and northwestern Iowa on Sunday and Sunday night. This will maintain generally southerly surface flow in our area, while the heat dome aloft gradually approaches to our south and spreads warmer air over the region. This will push temperatures up further on Sunday, with highs in the upper 80s northeast to mid-90s southwest. Increasing humidity is also expected with the approach of the heat dome and gradual airmass modification, sending Heat Index values close to 100 degrees in some areas Sunday afternoon and evening. There is some possibility of thunderstorms developing on Sunday morning as nebulous ripples of vorticity move through the mid-level west southwesterly flow. However, once again with the forcing mechanisms being subtle and in a larger-scale environment characterized by a warm layer aloft and the nose of the low-level jet being northeast of our area, have held POPs at only 20% on Sunday morning.

LONG TERM /MONDAY THROUGH FRIDAY/

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 /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 626 AM CDT Sat Aug 29 2026

Showers and thunderstorms will move through most of the area this morning, and have included prevailing and TEMPO groups at the northern terminals (FOD/MCW/ALO) accordingly and a PROB30 group at DSM where confidence is somewhat lower, but amendments might still be needed for short-term timing and intensity trends. All showers/storms should dissipate/leave the area before 18Z, after which VFR conditions are forecast for the remainder of the TAF period. However, gusty south winds are expected through much of the afternoon, then overnight tonight surface winds will diminish but winds just off the deck will increase substantially after dark, resulting in LLWS of 35-45 KT for much of the night.

DMX WATCHES/WARNINGS/ADVISORIES

None.