textproduct: Des Moines

KEY MESSAGES

- Patchy fog over much of northern/north-central Iowa this morning, with pockets of isolated dense fog at times.

- Hot and humid conditions continue through today, with a Heat Advisory in effect for much of southern and central Iowa until this evening. Temperatures lower slightly Sunday/Monday, reducing overall heat impacts somewhat.

- Very low potential (<15%) for a few isolated storms in northwest Iowa today, otherwise dry. More widespread showers and thunderstorms possible on Sunday, with a low potential for severe weather.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 302 AM CDT Sat Sep 5 2026

Patchy fog has developed across portions of northern and north- central Iowa this morning, with localized areas of dense fog that has been more transient in nature over the last hour or two. The continuation of light winds and mostly clear skies will likely allow for further development of this fog generally north of Highway 30 through sunrise, before dissipating. While most of this fog is expected to be patchy, there is a possibility for increased coverage of dense fog given the aforementioned conditions, so will be monitoring this closely. Besides the fog, a shortwave passing through the Dakotas within the persistent broad mid-level ridge overhead, paired with an increasing low level jet and deep moisture convergence has led to thunderstorm development over eastern South Dakota, which is lifting northeast. This shortwave will gradually shift into Minnesota through the day, with showers and storms expected to continue during the morning and into the afternoon. General consensus via CAM guidance and most deterministic models indicate this activity staying north and west of Iowa today, though a few models try to expand coverage into northwest Iowa by late morning into the afternoon. A closer look at soundings feature high instability values around 4000-5000 J/kg and steep lapse rates around 7.5-8 C/km, but with generally weak flow and low level dry air, as well as a lack of forcing overhead. If storms can make it into Iowa and are able to maintain themselves, the primary concern would be gusty winds. Have leaned toward the drier solutions, but will monitor trends on radar in case an increase in PoPs is needed into northwest Iowa. One more day of the oppressive heat and humidity is anticipated today as the heat dome remains nearby, with forecast highs expected to top out in the low to mid 90s across much of Iowa, where a Heat Advisory remains in effect until this evening.

Another shortwave within the thermal ridge is anticipated to travel in closer proximity to Iowa late tonight and especially Sunday, with low level moisture transport increasing out of the southeast into the state that will pool against an arriving boundary into western Iowa. Showers and thunderstorms are expected as a result to develop and increase in coverage through the day. A ribbon of instability around 1000-2000+ J/kg over western Iowa, along with shear values around 25-35 knots suggest at least an isolated potential for strong to severe storms with this activity into the afternoon. Damaging winds again would be the primary potential hazard, though PWATs near 2 inches and warm cloud depths could also lead to localized areas of heavy rainfall. Another feature to note at the same time is an area of surface high pressure over the Upper Midwest that is forecast to sink further south, with its influence looking to include portions of eastern Iowa. This keeps chances of shower/storm activity in these areas lower, where any changes in expected location of this feature, such as a further eastern shift could increase shower and storm coverage over Iowa, so something to continue watching. Thicker cloud cover overhead and the shower/storm activity will aid to keep temperatures noticeably cooler than in recent days, with forecast highs expected in the 80s that will essentially end the long streak of heat headlines, at least for a short time.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 234 PM CDT Fri Sep 4 2026

Early next week the western US trough will deepen and organize, pushing east. This will create an opportunity for more organized convection early in the week with increased shear and upper level support across the area. The main cool front associated with the system pushes across Iowa Tuesday and Wednesday, bringing temperatures down a few degrees by late week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1238 PM CDT Sat Sep 5 2026

A wide assortment of aviation conditions are across Iowa to begin the period. IFR to LIFR stratus is in the KMCW/KALO areas. An outflow boundary is moving into central Iowa and near KDSM and just west of KMCW. Some uncertainly if this will help clear the stratus at KMCW and the recovery to synoptic scale winds elsewhere as the outflow mixes out. The remainder of the terminal period focuses on additional thunderstorm chances later tonight and into Sunday morning, mainly at KFOD/KDSM/KMCW.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 7 PM CDT this evening for IAZ033>039- 044>050-057>062-070>075-081>086-092>097.