textproduct: Des Moines

KEY MESSAGES

- Two more rounds of rainfall beginning tonight/Saturday morning and again Saturday night and Sunday morning. Areas with heavy rainfall are possible.

- 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 SATURDAY NIGHT/

Issued at 200 PM CDT Fri Sep 25 2026

Precipitation chances and amounts are the challenge through at least Saturday night then again late Monday night through mid next week. Widespread rain has been ongoing this morning and into early this afternoon, mainly along and south of Highway 30. The rain will gradually diminish over the remainder of this afternoon as dry air entrainment begins and forcing continues to diminish. Rainfall with this activity has been quite efficient and has resulted in a band of 1.00" to 1.50" west of the Des Moines metro along the Highway 141 corridor.

Expecting two more periods of showers and storms from tonight into Saturday night. Each round will be driven by an increasing nocturnal low level jet and associated waves of theta-e advection along with short wave fragments. For tonight, a 35 to 40 kt low level jet will develop and similar to last night, the overall instability and mid- level lapse rates (~5.5 C/km) are weak, therefore, any potential for lightning is low, but non-zero over western parts of Iowa. PWATs will be higher tonight and in the 1.50" to 1.75" range and the 850 mb dew points will be near 12C. Warm cloud depths will be around 12500 ft. The combination of all of the above will result in another round of efficient rainfall processes and with more moisture available and a strong low level jet, max rainfall amounts will likely exceed today's totals with the most likely location being over west central Iowa and just west of Ames/Des Moines metro. Of note, a large High pressure system remains over the Great Lakes region and ridged south into Illinois. A wave of drier air will be moving westward tonight into early Saturday morning. At this time, the collision of moisture advection east/northeast and the dry air appears to occur over far northeast/east central Iowa and this will be the area where precipitation will struggle to advance further. This zone is also east of the forecast area, so the confidence in precipitation over much of the forecast area is high and adjusted the PoPs accordingly.

The next round of precipitation will begin late afternoon to early evening over western Iowa. Convective instability will be greater along with increasing mid-level lapse rates. Confidence in thunderstorms is greater as well over the western half of Iowa before the instability wanes to the east. The low level jet and short wave energy will fuel precipitation through the night. The deeper convection and the nearly stagnant to weak corfidi vectors and slow storm motions could promote heavy rain potential, especially if training of storms/precipitation does occur. This may be an accumulative effect with total rainfall amounts since early this morning top 4-5 inches in some spots of west central to central Iowa. While this may not result in flash flooding, significant rises on area streams and rivers are possible including along the Raccoon, North and Middle rivers in addition to the smaller urban related streams. Significant ponding is also likely.

LONG TERM /SUNDAY THROUGH THURSDAY/

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 /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1235 PM CDT Fri Sep 25 2026

Showers will be moving across the KDMX/KOTM areas through mid afternoon and will be in vicinity of KFOD. IFR or lower cigs/vsbys are possible at times. VFR with a few periods of MVFR cigs are expected at KMCW/KALO this afternoon. Another round of precipitation and lowering cigs arrives tonight and will persist into Saturday morning. This round of precipitation is expected to impact all sites. Southeast wind is expected through the period. A few gusts may occur late Saturday morning.

DMX WATCHES/WARNINGS/ADVISORIES

None.