textproduct: Des Moines

KEY MESSAGES

- Dry and pleasant during the daytime today!

- Thunderstorms return tonight into Tuesday. A few strong storms are possible along with locally heavy rainfall.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 305 AM CDT Mon Aug 17 2026

High pressure is centered over eastern Nebraska this morning with the influence of the high pressure extending into Iowa. Very light north winds to calm conditions extend across much of the state and the only clouds over the state is shear anvil cirrus from storms over southwest Kansas. The area of high pressure will move east across Iowa today and for the first time in numerous days, the forecast area will remain dry through the core daytime hours. High temperatures will again be pleasant and in the upper 70s to low 80s along with dew points in the 60s. Upper level low pressure will descend into northern Ontario today and will swing a short wave into the Northern Plains later today and towards Iowa tonight followed by another short wave on Tuesday. The surface high pressure will begin to become more positively tilted this afternoon and overnight and that will allow for return flow and theta-e advection to reach northwest Iowa. Thunderstorms are expected to develop over parts of South Dakota and Minnesota this afternoon along a surface cold front and attendant instability axis. These storms will track east/southeast and should reach parts of northern Iowa overnight. These storms will outrun the surface instability and will also run into remnant dry air over central Iowa from the departing high. While elevated instability will remain, the lack of the low level jet (LLJ) focus weakening/diminishing storms as they move further south into Iowa. The storms likely won't be able to maintain balance and will be trending outflow dominant as they arrive into Iowa. While a damaging wind gust is possible over northwest Iowa, the severe threat will continue to lessen deeper into the state.

Another area of storms to monitor will be the storms that will be more closely associated with the LLJ that develop over western South Dakota and Nebraska later in the night ahead of the 2nd short wave. The kinematic forcing will move east and could maintain the storms into Iowa late tonight and into Tuesday morning. These storms could hold a damaging wind threat longer than the earlier mentioned storms. The surface warm front should stay south of Iowa on Tuesday due to the early morning storms and the area of low pressure across eastern Colorado/western Kansas being suppressed further south during the day. This should push the supercell tornadic potential south. There is the potential for surface instability recovery by Tuesday afternoon. Light surface flow is expected but good speed shear aloft will exist which could promote organized convection. Low level instability along with the light surface flow up to cloud bases could promote horizontal vorticity stretching for landspout funnel potential. Cannot discount a large hail and damaging wind threat either. Moisture recovery will bring PWAT values back to near 2 inches over the southern half of Iowa and that may lead to locally heavy rainfall, especially in areas with repeated storms.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Issued at 1249 PM CDT Sun Aug 16 2026

From Wednesday through Friday, Iowa will continue to reside beneath northwesterly 500 MB steering flow, though which at least two more shortwave impulses will travel overhead. At the surface, however, the old decayed frontal zone should be pushed to our south over Missouri by convective outflows from Tuesday/Tuesday night storms. Additional showers may linger in our southern counties Wednesday into Wednesday night, but then decrease from Thursday onward with generally 10-30% POPs in the extended. The quick passage of a surface ridge along with light northwesterly flow should also allow for somewhat cooler weather, with daily highs generally in the 70s to lower 80s, though dewpoints will likely remain in the 60s to lower 70s. There are some indications that next weekend a larger surface high pressure system will build into the Upper Midwest and Great Lakes region, which if this occurs, may provide more tangible relief from the humidity that has persisted for the past few weeks.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 622 AM CDT Mon Aug 17 2026

Local fog near KFOD to start the period and this will diminish quickly this morning. Otherwise, VFR conditions today with light westerly wind. The wind will turn southerly overnight. Scattered thunderstorms are possible towards the end of the period at KMCW/KFOD/KDSM.

DMX WATCHES/WARNINGS/ADVISORIES

None.