textproduct: Des Moines

KEY MESSAGES

- Scattered showers and thunderstorms are possible at times tonight into Sunday, mainly in western Iowa. Severe weather is not anticipated during this time.

- Showers and thunderstorms will become more widespread by Sunday night into early Monday. Hail and strong winds will be possible mainly in parts of southern and western Iowa. Locally heavy rainfall is also expected, and may lead to ponding or minor flooding in some areas.

- There is the potential for a significant severe weather event on Monday, including the possibility of tornadoes, however the location of the threat remains uncertain and may range from central/eastern Iowa to parts of Missouri or Illinois. Stay tuned for updates on this threat over the next couple of days.

SHORT TERM /THROUGH SUNDAY/

Issued at 254 PM CDT Sat Apr 25 2026

A large 500 MB gyre remains parked over southeastern Saskatchewan this morning, with Iowa lying beneath the fringes of west southwesterly, broadly cyclonic flow around the system. A shortwave impulse rounding the base of the flow is moving across parts of South Dakota toward Minnesota, collocating with 850-700 MB theta-e advection to produce a broad swath of clouds and light rain stretching from Nebraska northeastward into Minnesota. At the surface, a large high pressure area has slide off to our east and is anchored over the Lake Michigan region, providing easterly low-level flow and dry air entrainment that is keeping the clouds/light rain off to the northwest of our service area so far. The result has been a dry, mild, and mostly sunny day with temperatures climbing into the lower 70s across much of Iowa.

While the leading upper-level impulse will move away to our north/northeast late today, the broad zone of theta-e advection will shift gradually eastward today and lie across Iowa tonight into Sunday. This is already manifesting in showers and thunderstorms developing in far eastern Nebraska and some of the CAMS drift this into our western counties late this evening, then bubble convection over us tonight and into Sunday. That being said, the persistent dry air entrainment from the east as well as a relative lack and the broad and nebulous nature of the forcing should result in low coverage and intensity of any convection that does occur. CAMs depict only spotty light echoes, and this is in line with expectation of isolated to widely scattered light showers and a couple of thunderstorms from tonight into Sunday. This is manifested in lower (generally 20-30%) POPs during that time, mainly over the western half or so of our forecast area, with no expectations of strong storms or severe weather through at least Sunday morning.

A robust mid/upper wave approaching the California coast today will come ashore tonight, then translate east northeastward Sunday and Monday as it interacts with the Canadian gyre, which will finally begin to ooze away to the northeast during that time. As this wave moves across the western and into the central U.S., it will cause mid-level flow over Iowa to gradually turn to southwest and increase from Sunday into Monday, and will also include surface cyclogenesis along the lee of the Rockies on Sunday. A surge of moisture transport and forcing for ascent associated with the approach of the wave will develop over parts of Kansas into Nebraska early Sunday, then spread northeastward into Iowa later in the day and especially Sunday night. This will cause a significant increase in convective/precipitation coverage across our area, resulting in near 100% PoPs by Sunday night.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 254 PM CDT Sat Apr 25 2026

By sunset Sunday evening the surface low will be centered near the southeastern corner of Colorado, with an inverted trough developing northeastward from it toward Iowa. On Sunday night the low will begin to migrate/pivot northeastward along the trough, reaching northeastern Kansas by sunrise Monday. Ahead of the low, precipitation/convection will overspread Iowa Sunday night within a region of robust moisture transport, persistent thera-e advection, broad upper level diffluence and forcing for ascent. The result will be widespread precipitation/convection across Iowa for much of the night, likely coming in several rounds first with the initial surge of moisture/warm theta-e aloft, then as a resurgence when a nocturnal low-level jet develops. The strengthening winds aloft will provide increasing deep-layer shear which, in spite of limited instability, will support some organized updrafts especially in parts of southern and western Iowa where MUCAPE may exceed 1000 J/KG at times. Decent mid-level lapse rates and the possibility of rotating updrafts support a hail threat from elevated storms overnight, and given the strength of winds just off the deck (roughly 40-45 KT at 3-4 KFT), if any organized clusters can establish a cold pool and transport momentum to the surface, then strong wind gusts may be possible as well. In addition to the possibility of severe weather, locally heavy rain is increasingly likely Sunday night and may result in ponding and minor flooding in some areas. See the HYDROLOGY section below for details.

On Monday the 500 MB wave and surface low will move directly over Iowa as a mature classic cyclone. A cold front/dryline will trail southward from the surface low, either collocated or with the dryline just a little ahead of the front, providing a focus mechanism for particularly strong updrafts during the day and into the evening. There are still multiple details that are not clear, however. One is the exact track and timing of the parent system and boundaries, which will heavily influence the greatest threat area. Another is the degree to which Sunday night/Morning convective debris may lessen or move the severe thunderstorm risk. If the overnight storms lay down a cold pool it will likely be somewhere over southern Iowa or northern Missouri on Monday, and may shunt the instability needed for stronger updrafts into that area. Likewise, if the dry slot between morning storms and the following dryline/cold front is sufficiently clouded over, this may inhibit destabilization ahead of the boundary as well. However, the latter effect appears less likely given the strength of subsidence in the dry slot depicted by deterministic model guidance. Finally, the location of the boundary/ies through the day and the time at which convective initiation occurs will also be very impactful. The NAM continues to be the slowest/most westward with boundary location and also blows storms up earlier, resulting in prolonged potential for severe, discrete thunderstorms over our forecast area during the day. The GFS and many other solutions, meanwhile, have the boundary/ies farther east when convection initiates later in the afternoon, resulting in storms forming in our eastern counties and quickly moving out of our area into eastern Iowa and beyond. These trends will be very closely monitored over the next couple of days, because wherever and whenever storms develop along the dryline/cold front they will carry a risk of potentially significant severe weather. Low- level shear and helicity will be maximized and easily support a tornado threat, along with strong mid/upper level winds that will also support supercells with large hail and damaging wind threats in addition to the tornado threat.

Once the cyclone moves through Monday and away Monday night, generally quieter weather will return for the remainder of the coming week. Opportunities for rain will be less frequent and overall lighter, while cooler weather will prevail from Tuesday through at least Friday. This will include daily lows generally in the mid-30s to lower 40s, leading to potential for frost and freezing temperatures at times.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1224 PM CDT Sat Apr 25 2026

VFR conditions will prevail through the TAF period, with a gradual increase in high level clouds this evening and tonight. There is an area of low ceilings around FL030-035 over eastern Nebraska that is attempting to creep eastward into Iowa, but it is encountering dry easterly flow that is eroding its leading edge and the probability is low that it will be able to reach DSM. In addition, isolated SHRA/TSRA will be possible tonight into Sunday, but probability of impact at any terminal is too low for TAF mention at this time.

HYDROLOGY

Issued at 254 PM CDT Sat Apr 25 2026

Two regions of QPF maxes present in the forecast for Sunday night into early Monday morning. The first of which will be in portions of western and northwest Iowa. This is where QPF favors a more blanketed, uniform amount due to the distance from the instability axis. Deep saturation and warm clouds depths to around 3kft paired with PWATs of around 1.25" will support efficient rainfall production. This region of the state is the most primed to take rain, especially rain at a relatively steadier rate such as this. The 40cm soil moisture percentiles are below 10% with many places below 2%. As for rivers affected, higher rainfall amounts will fall in the basins of the North Raccoon and the West Fork Des Moines. Gages in this region indicate normal to below normal discharge, indicating there is capacity for rain. Most QPF scenarios keep rivers at action stage or lower, with the East Fork Des Moines River approaching Minor Flood Stage if they receive the maximum qpf rain (>2"). Flash flooding impacts will be minimal in this area due to the rainfall rates being under an inch per hour

Another area to watch will be in southern and into central Iowa where a thunderstorm complex will form on the CAPE gradient. Corfidi vectors point to the east and southeast, allowing for training along the LLJ and some southward push on the boundary. Highest confidence is along and south of Highway 34. Convective processes will allow for higher rainfall rates. Cloud layer shear of 40kts and effective SRH may lead to supercell development overnight; these storms pose the best risk for 1" hour rainfall rates. REFS ensemble guidance has local maximum of up to 4" of rain along the front. Far southern Iowa also has higher soil capacity (below 30%). Rivers are above normal in flow, but if rain falls in the highest confidence area mentioned above, even worst case basin averages bring rivers such as the Chariton and Thompson just into action stage. A more northern shift would mean an increase in river and flash flood impacts, mainly due to higher soil moisture content and FFG under 2 inches. Contingency QPF on the Raccoon and Skunk basins bring them more easily into Action stage if basin-average rainfall exceeds 1".

DMX WATCHES/WARNINGS/ADVISORIES

None.