textproduct: Des Moines

KEY MESSAGES

- Severe thunderstorm and heavy rain potential this afternoon into the evening, initially over south central Iowa then more widespread overnight into Sunday morning.

- Dry and breezy during the day Sunday. Additional storms develop in western and northwestern Iowa in the evening, then spreading eastward into much of Iowa overnight into Monday.

- One final round of storms expected later Monday into early Tuesday morning. Severe weather and heavy rainfall looks likely.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 330 PM CDT Sat May 16 2026

Current conditions in the central U.S. shows surface low pressure over Kansas and the Texas & Oklahoma panhandles, advecting warm, moist air up into southern Iowa. Farther north, a surface high is working cooler, drier air south and east over Minnesota and northern Iowa. On the periphery of these two air masses, a gradient of 2000 to 3000 J/kg of SBCAPE has developed from the I-80 corridor and south, and is co-located with 40 to 50 kts of effective shear. A subtle wind shift is in place along this region, and is expected to become the focal point for storms this afternoon and evening. Guidance has struggled with the placement of this wind shift and the location of convective initiation still today, with the trend seeming to be farther and farther south with each round of guidance. Current consensus is that storms will fire over south western into south central Iowa within the next few hours, generally around 21 to 22z. These initial storms will have access to the highly unstable and deeply sheared environment, with access to 200+ m2/s2 of SRH within the 0-3 km layer, supporting rotating updrafts and supercellular storms. DCAPE values will also be modest, with SPC mesoanalysis implying 1000+ J/kg along southern Iowa. Both of these factors indicate a potential for severe hail and strong winds with any of the initial storms that develop. Rotating updrafts will also be conducive for tornadogenesis, thanks to the 100+ J/kg of 0-3km CAPE and low LCLs, but the low level wind fields do seem like a limiting factor. The high 0-3 SRH is almost entirely driven by the 1 to 3 km layer, while the lowest kilometer exhibits less favorable easterly winds to the north of the wind shift and minimal SRH from 0-1 km. That said, the southeasterly winds just to our south would make for a low level wind field more favorable for tornado development. Therefore, will need to watch surface observations closely, as any discrete storms ingesting that more southeasterly flow could lead to a better chance for tornadoes.

Storms initially begin discrete this afternoon, but storm motions along the boundary and the broad area of lift and instability will lead to many competing updrafts and a conglomeration of convection through the evening. This should mostly limit the severe risk for our area, as we become cut off from the uncontaminated warm sector. An east west oriented area of rain and thunder will develop, likely over southern Iowa into northern Missouri, resulting in a few hours of heavy rain within the same areas that saw the initial storms. Healthy precipitable water values in the 1.4" to 1.5" range will allow for heavy rainfall in these areas. This, in conjunction with the long duration of training storms, will lead to a swath of higher rainfall amounts. Earlier this morning, this swath was showing a widespread 2 to 3 inches of rainfall with some embedded pockets of 5 inches or more. This afternoon, this same signal still exists, but the southerly trend in guidance has been pushing the heaviest swath along the Iowa/Missouri border and southward. This should allow the heaviest rain to avoid the Des Moines metro areas, and fall over more rural areas where conditions have been dry and more capacity exists. That said, if any of these pockets of heavy rainfall falls over a more urban area/town, ponding on roads may still occur. Likewise, if the bullseye of 6 to 7" that has shown up in a few CAMs occurs, even in rural areas, some localized ponding or flooding could be a concern. This has prompted a slight risk for excessive rainfall from the weather prediction center over southern Iowa, although the highest likelihood at this time still looks to be south of our area.

Finally, as we get later into the evening, the guidance continues to prog an MCS coming out of Nebraska and into western Iowa overnight tonight into early Sunday morning. This MCS will roughly track along the east west oriented area of rain as it lifts northward overnight, leading to a roughly east northeasterly track across the area. Model wind gust output and storm modes would suggest this north south oriented line with the MCS could produce severe winds across Nebraska but generally diminishes upon reaching Iowa early Sunday morning. However, models are notoriously bad at modeling MCSs so it's certainly within the realm of possibility that these winds persist into Iowa as well. Fortunately, this time of night will be lending itself to decoupling and more elevated storms. Likewise, this will be moving into a fairly worked over and less stable environment. Therefore, a diminishing trend looks likely through Sunday morning, but not ruling out some strong winds as it initially moves in.

The rain and thunderstorm activity moves out through Sunday morning, with dry conditions expected over much of the state during the day on Sunday. Relatively strong capping will inhibit the unstable environment during the day, with storm development primarily occurring in the evening and overnight hours. That said, gusty conditions develop during the day Sunday across most of Iowa as stronger winds aloft move into the area. Winds of 20 to 30 mph are expected, with gusts nearing 40 mph possible at times.

Yet another round of thunderstorms will move into western Iowa in the late evening to overnight hours Sunday as the surface low lifts northeastward through Nebraska into western Iowa. This synoptic lift and weakening cap will allow storms to go over northwestern Iowa, with potential for more supercells capable of producing large hail, damaging winds and tornadoes. That said, by the time these storms look to arrive in our forecast area, the instability will be diminishing and storms congealing into a line. Therefore, the main tornado threat will be over far western and northwestern Iowa Sunday evening, with mostly a wind threat farther eastward into Iowa through the overnight hours. Driven by the low level jet, storms persist overnight into early Monday, but the severe risk looks fairly isolated.

LONG TERM /MONDAY THROUGH SATURDAY/

Issued at 330 PM CDT Sat May 16 2026

The encore system will lift through the area on Monday, bringing the potential for widespread storms and heavy rainfall. Severe weather looks likely with this system, as the parameter space boasts 60+ dewpoints, very unstable, surface based conditions, and a good amount of kinematic support along the cool front passing west to east through the area. All severe hazards will be possible, including hail, damaging winds and tornadoes. Strong moisture transport will also lift into the warm sector of the Monday system, bringing plenty of liquid into the area. Storms should be fairly progressive along the cold front, but localized ponding or flash flooding is certainly possible, especially in areas that receive rainfall tonight and Sunday night as well. Likewise, more water being added to local rivers could lead to in-bank rises through next week. We then see a brief break in the active pattern through the middle of the week, with milder temperatures overhead.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 645 PM CDT Sat May 16 2026

Thunderstorms have developed over southern Iowa and are starting to lift towards KOTM. Additional scattered showers/storms are expected to continue to develop through the evening with more widespread activity moving in overnight. There remains less certainty with where/when scattered activity, outside of the storms in southern Iowa, will develop thus used mix of tempo or prob30 groups where certainly is less. Updates are expected as confidence in coverage/timing increases. The activity overnight will likely be accompanied by lowering visibilities with heavy rain at times, and overall lowering ceilings with MVFR to even IFR conditions at times in portions of central to northern Iowa. Strong wind gusts are also possible, but are not currently reflected due to lower confidence in timing and intensity. Precipitation moves out Sunday morning with windy conditions out of the south-southeast expected during the day.

DMX WATCHES/WARNINGS/ADVISORIES

None.