textproduct: Des Moines

KEY MESSAGES

- Rain chances lingering through the day today and another round of heavier rain tonight. Highest amounts in central and southern Iowa.

- Another potent system arrives Monday night and through mid week. Additional areas of heavy rain may occur.

- Monitoring potential accumulative impacts on area streams and rivers. Significant rises are expected on some streams, potentially reaching flood stage or higher by mid next week.

SHORT TERM /THROUGH SUNDAY/

Issued at 258 AM CDT Sat Sep 26 2026

A closed low was circulating over southern Canada overnight and a negatively-tilted segment was analyzed over the Central Plains. The primary instability axis is states away and only a handful of lightning strikes can be found this far north. Warmer midlevel temperatures remain locked behind the leading shortwave segment, residing over the Rockies, meaning lapse rates will lean more towards the moist adiabat in the midlevels and CAPE values will stay mainly under 1000 J/kg. The midlevel wind field also remains weak with the upper jet more collocated with the main trough in the Intermountain West. These two factors mean that the risk for severe weather is low over the weekend. That said, concerns for heavy rainfall remain. While the weak convective processes will help curb the rainfall amounts, moisture content, the synoptic setup, and weak flow will keep efficiency high.

00z CAMs trended more localized rather than widespread QPF swaths and their simulated location differed. The conceptual model favors the QPF max to the main convergence along the low-level jet. In fact, won't leave completely during the day today. Rain chances will persist and increase as the LLJ max reestablishes itself at sunset. Slow-moving storms will produce heavy rain overnight and mostly likely be found somewhere across central and southern Iowa; this is the same part of the state that has seen the most rainfall already this month. Ponding is likely and the flash flood potential is lower due to the weaker convective processes limiting rainfall rates. Concerns are more in river flooding. Basins mentioned in the previous discussion remain the main concern tonight: the Raccoon, North and Middle rivers. Soil moisture percentiles in these basins are over 80%, meaning that much of the rain received this weekend and beyond will become runoff. That being said, given the downtrend in QPF this weekend, it may be more of a primer for the rainfall during the work week.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 200 PM CDT Fri Sep 25 2026

Precipitation chances will diminish during the day Sunday from west to east. Monday is expected to be mostly dry but that dry weather will be short lived as another potent system impacts the state. An upper low pressure system will dig into southern California on Monday then will transition into Arizona and New Mexico Monday night and Tuesday. That will create an amplified southwest flow over Iowa and create a Monsoonal flow moisture connection. While this is ongoing, a good connection to Gulf moisture will also be established with the two moisture sources overlapping across Iowa and push PWAT values back over 2", which is climatologically significant for late September. Shower and storm potential will increase Monday night and persist into Tuesday night. Heavy rainfall is possible which could further exacerbate hydrology conditions. Still monitoring the Wednesday and Thursday timeframe as the upper low translates into the Kansas region. Also during this timeframe, monitoring the potential for Hurricane Polo being ingested into the southwest flow ahead of the upper low, which is likely dependent on if that tropical system can maintain a northeast path across the Baja California. Should this occur, it could be a source for more heavy rainfall mid-week.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 642 AM CDT Sat Sep 26 2026

Rain is encompassing most of the area this morning, with less intensity for northeast terminals. Dry air at KMCW and KALO will work against vsby and cig restrictions today, hence they favor MVFR in the TAF. IFR vsbys have been uncommon this morning, so have favored MVFR. However, IFR cigs with pockets of LIFR possible. Improvements to MVFR expected through the afternoon. Have added in timing for rain and thunderstorms for after 00z.

DMX WATCHES/WARNINGS/ADVISORIES

None.