textproduct: Des Moines

KEY MESSAGES

- Rain and thunderstorms will spread from west/southeast to east/northeast across Iowa from late this afternoon into tonight, with some redevelopment overnight into Monday morning. Severe weather will be possible in southern and southwestern Iowa, mainly in the form of large hail. Locally heavy rainfall and minor flooding will also be possible in that area.

- Additional thunderstorms are likely on Monday, especially in the afternoon when severe weather will again be possible. Large hail is the most likely threat. Tornadoes will also be possible, some of which could be strong, along with damaging winds, but those threats are less certain due to lingering effects from overnight/morning storms. Please stay tuned to updates on this situation overnight into Monday.

SHORT TERM /THROUGH MONDAY/

Issued at 240 PM CDT Sun Apr 26 2026

A large 500 MB gyre is centered along the Saskatchewan/Manitoba border this afternoon, with a longwave trough trailing from it down the western U.S. Ahead of this trough, steering flow has turned to southwesterly over Iowa, with a shortwave impulse currently emerging from the Rockies onto the High Plains. Its approach is causing surface cyclogenesis in the lee of the Rockies, with a low developing over far northeastern New Mexico and southeastern Colorado. A large region of theta-e/moisture advection ahead of the trough is producing a swath of rain from around the Black Hills southeastward toward Kansas City, including some severe thunderstorms across northeastern Kansas.

As the trough approaches Iowa tonight, the swath of showers and storms will spread east/northeast across the state, reaching central Iowa by late this evening/early tonight. Behind this initial surge of forcing and precipitation, additional showers and storms will develop overnight into Monday morning in association not only with the broad forcing for ascent along the leading flank of the system, as well as the associated increasing moisture, but also with the development of the nocturnal low-level jet after midnight. It remains to be seen how high precipitation coverage will be behind the initial surge early in the night, however, given the extent of the lift and degree of saturation, categorical (80-100%) PoPs are maintained through most of the night into early Monday. As wind/shear fields increase overnight with the development of the LLJ, there will be some potential for organized updrafts and severe weather primarily in the form of hail. This may be mitigated somewhat by a relatively saturated column, but even so mid-level lapse rates are supportive of this threat. There may also be a narrow opportunity for more surface-based convection and strong winds, mainly in southwestern Iowa where the SPC has advertised a Slight Risk of severe weather appropriately. In addition, heavy rain will be possible overnight mainly in southern Iowa - as discussed in further detail in the Hydrology section below.

While scattered to numerous showers and storms are forecast over Iowa tonight into early Monday, one or more MCS's is anticipated across about the northern half of Missouri during that time. Initially the storms currently over northeastern Kansas are expected to translate eastward across Missouri, then overnight as the LLJ intensifies it will be primarily directed into Missouri with a second convective complex likely. The evolution, location, and maintenance of these storms into Monday morning will have significant impacts on the convective evolution and severe weather potential in Iowa and northern Missouri later Monday. The deepening surface cyclone mentioned above, currently in far northeastern NM/southeastern CO, will pivot northeastward across Kansas tonight and Iowa on Monday. As it moves through, it will trail a cold front/dry line boundary that will sweep eastward with the low. There is the potential for thunderstorms to develop near/within the core of the cyclone, at the triple- point, and also along the trailing front/boundary, and also within the preceding warm sector. In addition, it is possible that outflow from the overnight/Missouri MCS(s) may result in a baroclinic zone acting as an effective warm front, lifting northward on Monday and providing an additional focus mechanism for convective development. These various scenarios, many of which are dependent on storm evolution tonight, lead to a relatively low degree of confidence in the severe weather threat within our forecast area on Monday. However, what can be said with confidence is that the dynamic forcing associated with the trough/cyclone will be sufficient to generate thunderstorms in at leas parts of our area, even with minimal instability, and that strong wind and deep-layer shear fields will be supportive of strong updrafts and a severe weather threat. If convective debris from the overnight/morning storms is sufficient to inhibit insolation and destabilization, then these storms will remain elevated but still pose a large hail threat as they traverse our area. However, if enough clearing can occur, even for a short period, to allow for additional destabilization ahead of the approaching low/front such that surface-based convection occurs, then the possibility of strong winds and tornadoes would increase considerably. This potential is highest in our southern and southeastern counties, south of the low center track and where the trailing front will move through later in the afternoon. Watch closely for updates on the severe weather potential overnight and Monday morning.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 240 PM CDT Sun Apr 26 2026

Behind the passing storm system, late Monday into Monday night, winds will turn to west northwest and increase considerably due to a tight pressure gradient moving through Iowa. Have increased winds across our northern areas to 20-30 MPH with gusts of 30-40 MPH during this time, and at least sporadic higher gusts are likely. The winds will diminish relatively quickly however, by later Monday night, as the system moves away and a large high pressure ridge builds down the High Plains and toward Iowa. This will provide several days of cooler and relatively quiet weather, with just some low (~20%) shower chances around Wednesday/Thursday. Overnight lows will range in the mid-30s to lower 40s on four consecutive nights, from Tuesday night through Friday night, leading to the potential for a frost or even freeze in some areas. This will be fleshed out in the coming days as it will be dependent on cloud cover, winds, and other factors each night.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1219 PM CDT Sun Apr 26 2026

Very isolated SHRA/TSRA expected this afternoon, but with probability of impact at any given terminal too low/brief for TAF inclusion. Expect increased coverage/frequency of SHRA/TSRA from this evening into Monday morning, and have included mixture of prevailing/TEMPO/PROB30 groups accordingly, attempting to target most likely areas and time windows. Confidence in those details is relatively low however, so expect adjustments in later TAF issuances. Low MVFR or IFR ceilings are also likely by early Monday morning.

HYDROLOGY

Issued at 240 PM CDT Sun Apr 26 2026

Several rounds of thunderstorms are forecast from late today into Monday across parts of Missouri and Iowa. Moisture advection into the region will increase PWATS up to around 1.5" in southern Iowa overnight, however the strongest moisture transport is focused just south of the border over Missouri. It is also likely that one or more Mesoscale Convective Systems will cross the northern half of Missouri, which may further act to cut off moisture supply to the north, at least in a relative sense. Strengthening low-level winds will lead to increasing storm motion speeds, and it is also unclear whether any storms in southern Iowa will be able to train, or whether they will take the mode of intermittent, quick-moving elements. The latter scenario appears more likely and could still result in relatively heavy rainfall amounts in some areas, perhaps 2 inches or more, but likely spread out across multiple hours with relative breaks in between. With 3-hour FFG values in the 2.2-2.4" range in our southern counties, the result is a threat of heavy rainfall and localized ponding/minor flooding impacts overnight, but mitigated by the other factors. The WPC has maintained a Slight Risk of Excessive Rainfall overnight accordingly. If some of the mitigating factors do not evolve as expected and the threat of either significantly higher rainfall totals, or more persistent rainfall rates materializes, then a Flood Watch could become necessary later tonight.

DMX WATCHES/WARNINGS/ADVISORIES

None.