textproduct: Des Moines

KEY MESSAGES

- Generally quiet weather for the upcoming work week, with high temperatures in the low to mid-80s each day.

- Some light showers are possible across the western half of Iowa late tonight into Monday morning. A few showers and thunderstorms will also be possible on Tuesday into Tuesday night, with a low risk of severe weather just to our northeast in parts of Minnesota and Wisconsin.

- A more active weather pattern will return with additional thunderstorm chances next weekend, but any further details remain unclear at this range.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 108 PM CDT Sun Aug 23 2026

A large surface high pressure ridge dominates the region today, stretching from south central Canada down over the Upper Midwest and Iowa. The result is seasonally comfortable conditions, light and variable winds, and a lack of low-level clouds. Meanwhile, a large 500 MB heat dome is sitting over the Desert Southwest and southern High Plains, with a ridge extending northward into central Canada. Two relatively subtle shortwave impulses are overtopping this ridge, with a larger trough moving over the Washington/British Columbia region. The first of the two shortwaves is sliding southeastward across Nebraska at this time and producing light showers there, as well as some higher cirrus clouds that are streaming over central Iowa but only modestly blunting insolation. All in all it is a beautiful day for most outdoor interests in our area.

As the leading impulse slides from Nebraska into Kansas and Missouri later today, some of the showers over Nebraska may just clip the southwestern corner of our forecast area. However, dry air entrainment and subsidence associated with the surface ridge will inhibit any such eastward expansion, and recent regional radar trends support the rain staying just to our southwest so have kept the forecast dry through this evening except for some 20% POPs down by Taylor County. From tonight into Monday, as the second impulse moves overhead and in closer proximity, gradual saturation of the atmospheric column should support some light rain in our western and southwestern counties, mainly after midnight and into Monday morning. However, even then, there is a notable lack of instability and forecast soundings still show fairly substantial dry air to overcome, especially with the farther eastward one goes in our forecast area. With this in mind, have maintained relatively low (20-30%) POPs in our western counties from late tonight into early Monday, but have lowered them to 10% in our central counties and gone with light shower/sprinkle wording for the most part. No appreciable rainfall amounts are anticipated and severe weather is not expected.

On Monday the surface ridge will begin to drift off to our east, allowing for a return of light southerly flow. Modest ridging aloft, in wake of the overnight shortwave impulse, will cause any lingering showers to fade out by midday and lead to dry conditions Monday afternoon and evening. By sunset, the aforementioned larger 500 MB trough currently over Washington/British Columbia will have progressed to southeastern Saskatchewan, and will subsequently move east southeastward to near Lake Superior by Wednesday morning. As it does so, it will push a reflective surface trough southeastward through our region, crossing Iowa from late Tuesday through Tuesday night. Ahead of this surface trough, a period of modest forcing for ascent ahead of the 500 MB trough, concurrent with weak warm air/moisture advection in the low levels, supports a few showers and thunderstorms during the day Tuesday and have maintained 20% POPs accordingly. Around Tuesday evening, thunderstorms are expected to develop along the advancing surface trough closer to the 500 MB low, roughly near the Minnesota/Wisconsin border. In that region stronger instability and low-level convergence along the trough supports more robust updrafts and some severe weather potential, however, this is more in question heading southward down the trough into Iowa. The forcing associated with the parent low aloft will be weaker down here, and the surface boundary a bit more washed out with weaker low-level convergence. Forecast soundings also hint at possible capping in the afternoon and evening. As such, have held POPs low (again, 20%) in our northeastern counties and the SPC convective outlook keeps a Marginal Risk of severe weather just to the northeast of Iowa. However, we will be watching over the next couple days for any signs of southward expansion of that potential and of POPs in general. As the surface trough then sinks southeastward across our service area later Tuesday night, 20% POPs are maintained in that area to account for lingering showers and storms developing along it, but any severe weather potential would diminish even further overnight.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Issued at 108 PM CDT Sun Aug 23 2026

By Wednesday the large 500 MB heat dome will remain in place over the southwestern/south central CONUS, while the trough described in the SHORT TERM section above moves away to our east. This will allow deep-layer ridging to reassert itself just to our west, leading to a period of dry, quiet, and seasonally mild weather with daily highs in the low to mid-80s for the remainder of the week. By Friday and Saturday the pattern will begin to shift a bit, as two large 500 MB lows develop over Canada and shunt the ridge southward, with the heat dome retrograding more over the far southwestern CONUS near Arizona and New Mexico. This will cause 500 MB flow over Iowa to become more zonal, with multiple shortwave impulses moving through the flow and providing several opportunities for thunderstorms from Friday or Saturday into early the following week. While the details of any such storms are very uncertain at this range, it is fair to say that overall the weather pattern will be more active by next weekend.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1233 AM CDT Sun Aug 23 2026

VFR conditions are forecast with no aviation impacts anticipated. There is a very low (10-20%) chance of light rain at FOD/DSM late tonight into Monday, but between the low probability and the lack of notable impacts even if it were to occur, have not mentioned in the 18Z TAFs.

DMX WATCHES/WARNINGS/ADVISORIES

None.