textproduct: Des Moines

KEY MESSAGES

- Some uncertainty on shower and storm chances over southern Iowa tonight. A drier solution is favored but low chances (<25%) remain that rainfall amounts reach one inch or more over far southern Iowa.

- A few more storms late Saturday and Saturday night. A few severe storms may occur.

- Hot and Humid weather arrives Sunday and will persist much of next week. Heat headlines will likely be needed at times.

UPDATE

Issued at 624 AM CDT Thu Jun 25 2026

Forecast is largely on track this morning but did increase PoPs across the far southwestern portions of the CWA due to present radar trends.

SHORT TERM /THROUGH FRIDAY/

Issued at 232 PM CDT Thu Jun 25 2026

A few light showers have been eroding as they enter southern Iowa today while high pressure riding is over the remainder of the state. A broad cumulus area has developed in central and northern Iowa and has led to filtered sunshine at times and an overall seasonably cool day with temperatures in the 70s.

Water vapor imagery is showing an area of drying moving into western Kansas associated with a mid-level short wave. A broad area of showers and a few thunderstorms is ongoing over eastern Kansas and in an area where good moisture transport is overrunning a surface warm front that is located over northern Oklahoma. The 12z model suite hasn't handled the currently location of the warm front well at 18z, with many solutions too far north into Kansas. There remain varying solutions on strength and northern extent of the developing low level jet (LLJ) this evening also. For example, the NAM/ECWMF solutions have a much stronger branch lifting through Missouri with a sfc low reflecting developing along the northwest fringe of the jet. This would drive much more moisture towards southern Iowa late tonight into early Friday. Other solutions hold all of this south with the dry air arriving from high pressure ridging from the north limiting precipitation. This solution is supported by the CAMs and ensemble solutions such as the HREF and REFS. Currently favor the drier solution but will need to monitor the LLJ evolution this evening as the wetter solution could bring one inch plus precipitation to far southern Iowa. Residual cloud cover may linger over southeast Iowa through the day and limit high temperatures in that region with the warmest highs in the low 80s occurring over the northwest.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 232 PM CDT Thu Jun 25 2026

The extended forecast weather story remains the upcoming pattern change and the arrival of summer heat. As discussed several times now, the combination of upper low pressure moving into the Pacific Northwest and sub-tropical high developing over the lower Mississippi Valley will create steepening southwest flow and strong warm advection across Iowa late Saturday and Saturday night. A few elevated thunderstorms are possible but the moisture advection portion of the theta-e advection may be limited. This could lead to the elevated mixed layer becoming established more quickly and leaving no activation point for convective initiation. The latest model soundings do show some potential for storm development over southern Iowa and then lift north. Any storm development would pose an attendant large hail threat and potentially damaging winds should any gravity wave interaction occur.

The impending heat then is the main weather focus for Sunday and through much of next week. A stout EML will be in place on Sunday. The main upper level energy begins to eject northeast out of the Pacific Northwest on Monday and will force a boundary westward. There remains a low chance that the boundary moves far enough east for thunderstorm chances to reach northwest Iowa late Monday and Monday night. The upper low will flatten the top of the upper ridge mid next week and may bring a brief periods of ring of fire MCS development that could impact northern Iowa. This could also impact high temperatures into that part of the state mid-week and bring a brief reprieve to the heat before it resumes for the entire state moving into the end of the week and into the holiday weekend.

High temperatures by the NBM Sunday and early next week may be a touch high though it is currently running with a cooler bias due to recent weather. In addition, northwest Iowa has been relatively dry this month and that will also be the region closer to the thermal ridge so if good mixing occurs, temperatures may approach these values. As noted above, the EML will be in place at times and that will limit the mixing depths to below 850 mb at times so despite the impressive 850 mb temperatures in the mid 20s Celsius range, these may not be fully realized at the surface as those may remain in the EML area. Dew point values are more interesting. The Gulf flow becomes wide open into Iowa and dew points well in the 70s have resided in the recent warm sectors to the south that had access to Gulf flow. In addition, evapotranspiration of the Iowa crops is beginning to take off now that rapid growth rates are now taking place. This will further accelerate next week. Therefore, dewpoints well in the 70s are likely as moisture becomes trapped below the EML with limited options to mix these out. Raw model guidance from the NAM/GFS/ECMWF/SREF have 75+ dew points for Sunday afternoon as a theta-e plume moves across the state. The combination of these higher dew points and high temperatures in the 90s, will create heat index values above 100 common from Sunday through much of next week and will require heat headlines at times as we move into a prolonged period of heat.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1231 PM CDT Thu Jun 25 2026

Cumulus is developing over central and northern Iowa though bases are now above 3kft. A period of BKN cumulus is possible at KMCW/KALO but cigs should remain VFR. Some of this cumulus may transition to more stratocumulus for the overnight along with increasing mid-level cigs AOA 10kft. Showers and a few thunderstorms are possible later tonight over southern Iowa and may impact KDSM/KOTM and have included Prob30 mention at each site. MVFR cigs may also occur at those sites. Northerly wind this afternoon will remain below 12 kts then will become light northeast tonight.

DMX WATCHES/WARNINGS/ADVISORIES

None.