textproduct: Des Moines

KEY MESSAGES

- Breezy winds with gusts up to 35 mph possible through late this afternoon with a very low chance (<20%) of a few isolated showers or perhaps storms.

- Increasing late season heat and humidity Sunday into much of next week, especially over southern Iowa where heat index values will be around 100 degrees at times.

- By no means a wet period, but there will be additional storm chances up to 40% at times tonight into at least the middle of next week with peak timing of chances mainly overnight into the early morning hours.

SHORT TERM /THROUGH MONDAY/

Issued at 216 PM CDT Sat Aug 29 2026

Numerous features are apparent on GOES-East upper level water vapor imagery with several cyclonic spins - two along or just off the West Coast within a mean broad scale trough and another rotating over the Quebec and Ontario provinces. Our decayed storm system, which overtopped the mid-level ridge axis which has spread eastward into the Middle Mississippi River Valley, brought overall welcomed rainfall due to the recent dryness to northern and parts of central Iowa. The showers and storms have since largely dissipated or moved out of central Iowa, though a few spotty showers or isolated storms remain possible this afternoon. Otherwise, there has been some clearing, which has allowed for sunshine to turn the temperatures upward quickly. Highs are on track for the 80s - around 80 degrees over northeastern Iowa and well into the 80s to near 90 degrees over southwestern Iowa. Winds have been breezy as forecast as boundary layer mixing has tapped into the weakening winds at the top of this layer. Thus, winds have been sustained between 10 and 20 mph and gusts up to around 30 to 35 mph.

As we head into tonight, the 850mb low level jet will be over Iowa and nosing into southern Wisconsin. Instability will be lessening through the night and shear will be lacking such that expectations are mainly dry overnight. More nebulous ribbons of shortwave energy will pass overhead in concert with a the weakening nocturnal low level jet during the day Sunday and this may offer a slightly higher chance (20-35%) for spotty showers and storms. However, this activity will be fighting against increasing warm layer capping as the 500mb heights increase at the same time. This same pattern may repeat late Sunday night into Monday with the next round of ill- defined energy topping the ridge with weak instability and shear and the low level jet once again nosing into Wisconsin. Summarizing, while there are chances for a few storms tonight through Monday, the current forecast would have odds favoring a dry forecast for many. On the temperature side, the increasing heights on Sunday into Monday spell warmer conditions. However, initial National Blend of Models (NBM) raised highs 3 to 4 degrees over the previous forecast. Investigation showed this was above the 90th and 75th percentile Sunday and Monday, respectively, which pushed highs well into the 90s to even 100 degrees. Part of these warm NBM temperatures may be due to the influence of the way too warm GFS and its ensemble. For historical reference, if 100 degrees occurred at Lamoni, this would be one of the latest 100 degree or higher days on its record. Thus, forecast high temperatures were tuned down both Monday and Tuesday in collaboration with southern neighboring offices.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Issued at 216 PM CDT Sat Aug 29 2026

The mid-level ridge will be drifting and lifting northeastward becoming centered over the St. Louis area by Tuesday. The broad trough in the western US will persist keeping our low level flow from the southwest and the storm track passing over northern portions of the state with a surface quasi-stationary boundary in place in that vicinity as well. The sensible weather effects will be drier and warmer conditions over southern Iowa with opportunities for storm chances over northern Iowa with a timing peaking likely overnight into the early morning hours. This is not a forecast to be very specific with fine tuning of the details such as timing and location in the coming days. What seems more confident is the late- season heat with potential for several days of record warm low temperatures possibly in jeopardy, pending any convective development farther south in Iowa and cloud debris contamination. While heat index values never breach the 105 degree advisory criteria, there will be multiple days of values peaking in the 100- 103 degree range over southern Iowa paired with low temperatures in the upper 70s through at least Wednesday. Experimental heat risk is in the extreme category (level 4 of max of 4) over many portions of southern Iowa during this period, which aligns with the magnitude of the uncommon late season heat and high low temperatures. Those with vulnerabilities to heat will want to take precautions through this upcoming week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 12025 PM CDT Sat Aug 29 2026

Showers are or will soon depart the OTM with a dry forecast prevailing thereafter along with VFR conditions. Breezy winds with gusts between 20 and 30 knots will be common through this afternoon before diminishing this evening. Low level winds, though, will be increasing and create a period of low level wind shear from mid-evening through around sunrise Sunday morning.

DMX WATCHES/WARNINGS/ADVISORIES

None.