textproduct: Des Moines

KEY MESSAGES

- Light showers and possibly a brief thunderstorm are forecast across southern Iowa today (20-40% chances of rain), but any rainfall will be spotty and generally light.

- More showers and storms are forecast late Saturday and Saturday night. A few severe storms may be possible during this time.

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

SHORT TERM /THROUGH SATURDAY/

Issued at 103 AM CDT Fri Jun 26 2026

A 500 MB shortwave impulse is traveling eastward across the region this morning, resulting in expanding cloud cover and broad but weak forcing for ascent. At the surface however, a warm front remains well to our south across Kansas and MIssouri, with a high pressure area anchored over the western Great Lakes region extending its influence into Iowa. This is resulting in light winds and a layer of drier air that is helping to undercut any developing precipitation, resulting in light and spotty radar echoes that are only intermittently reaching the ground and producing any measurable rainfall. Once such area is in our southeastern counties and adjacent portions of Missouri and far southeastern Iowa, while another is moving over the tri-state area of NE/SD/IA and into northwestern Iowa. Some short-range models and CAMS still attempt to expand and intensify the former area of rain across southern Iowa early this morning and even lingering through today into tonight in some cases, but it is more likely that any appreciable moisture will remain cut off to our south where the nocturnal LLJ is focused around the aforementioned warm front. Have thus trended PoPs a bit further downward and southward in our southern counties, maintaining just 20-40% rain chances with light QPF. Also included a couple hours of slight chance (20%) rain chances in our northwestern counties in deference to the light echoes approaching from Siouxland, but these should fade out as the morning progresses.

Aside from PoPs, the other notable sensible weather today will be in the form of relatively cool temperatures once again, due to the light surface flow and prevalence of cloud cover. Late in the day as the 500 MB impulse begins to move off to our east, low-level flow will come around to southeasterly in our northwestern counties and some breaks in the clouds may occur there, so have maintained highs near 80 in that area. In our east and southeast, however, clouds will linger along with possibly a light shower or two, and have notched temperatures down another degree or two into the low/mid-70s in those areas accordingly.

On Saturday a 500 MB ridge will start to become established across the central U.S. and Midwest, bringing in warmer temperatures aloft. This will also induce the Great Lakes surface high to retreat eastward while a broad surface low pressure trough develops along the lee of the Rockies. Surface winds will come around to southeasterly across all of Iowa and temperatures will rise modestly, peaking in the lower 80s in most of our forecast area. This will herald the beginning of a notable and rapid shift in the weather pattern, making Saturday the last day of relatively comfortable temperatures before a much hotter period begins as discussed in the LONG TERM section below.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

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 for several days 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 /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 623 AM CDT Fri Jun 26 2026

VFR conditions will prevail through the TAF period. A few light showers or sprinkles will affect the area early this morning, but any visibility reductions will be brief and minimal. On Friday morning, right at or just before the end of the 12Z TAF period, MVFR ceilings may be possible at DSM and OTM but probability is currently too low (30% or less) to advertise in the TAFs at this range, and potential will be re-evaluated for later updates.

DMX WATCHES/WARNINGS/ADVISORIES

None.