textproduct: Des Moines

KEY MESSAGES

- Drizzle and fog continue to diminish from northwest to southeast over central Iowa through late today.

- Brighter skies, but still cool on Wednesday.

- Showers and occasional storms return from west to east Thursday or Friday before drier air arrives on Sunday. Conditions remain cool through first half of weekend.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 155 PM CDT Tue Sep 22 2026

The lead shortwave trough is moving toward Lake Michigan early this afternoon as evident on GOES-East upper level water vapor imagery. This has pulled most of the very spotty showers that were over our southeastern forecast area into eastern Iowa. However, clouds will remain through the day as low level saturation persists in the lowest 2km. Areas of drizzle and patchy fog will persist beneath these clouds in this saturation through at least this afternoon as it ends from northwest to southeast across central Iowa. The drizzle may need to be extended further into tonight given that RAP soundings show the saturation continuing until around midnight. The drier air does eventually arrive, albeit slowly, as the trailing shortwave trough moves through the state and high pressure influence noses in from the east finally. Despite the drier air moving in, relative humidity remains high and low chances of light fog remain, which is shown in the NBM and GFS MOS guidance. Forecast soundings show no full saturation at the surface so will forgo any fog mention at this time. However, if the sky does clear, this may increase fog chances and in addition may result in temperatures falling lower than forecast, such as northeastern Iowa into the low 40s.

With the drier air pushing westward through the morning Wednesday, skies will turn brighter first in eastern parts of our forecast area and then in western parts by midday Wednesday. Cross sections persist a thinning layer of low level moisture such that cumulus clouds may develop in the afternoon - particularly over eastern Iowa/along and east of I-35. This moisture will be beneath a ridge axis that will poke up into Siouxland at least keeping conditions dry through the day. However, a shortwave trough lifting northeastward will tamp back down the ridge and bring a return of higher atmospheric moisture into the state. Further, a ribbon of modest QG convergence will spread over western into central Iowa with a few pulses of theta-e advection. This will prompt scattered showers and storms to arrive over western Iowa in the early morning hours of Thursday. At this time, these may be confined to mainly the western half of the state through the day where the stronger forcing will reside along with light, southeasterly flow that will funnel in low level drier air from surface high pressure over the Great Lakes. The low level jet pointed into eastern Nebraska will keep scattered showers and storms going over the western part of the state Thursday evening, but as that veers toward Iowa late Thursday night/early Friday morning this activity may start to spread farther eastward into the state. Severe weather is unlikely given weak instability and lapse rates, though efficient rainfall may be possible with high precipitable water values and deep warm cloud depths.

LONG TERM /FRIDAY THROUGH MONDAY/

Issued at 155 PM CDT Tue Sep 22 2026

Intermittent showers and storms will persist Friday into Saturday as low level QG convergence and theta-e advection slowly move eastward. While it will not be days full of rainfall, the days will be more common to the ones we have had recently with plenty of clouds and times of precipitation. While there will be instability for occasional storms, the higher instability and overlapping shear is displaced west of the area. Thus, locally heavy rainfall continues to be the main concern due to the antecedent wet conditions. While soils will have a 24 to 48 hours break with dry conditions, infiltration capacity will remain reduced along with elevated streamflows. Rainfall totals still look on track between 1 and 3 inches on the high end with ensemble probabilities of a 1" of rainfall in 24 hours between 45 and 55% over western Iowa Friday morning into Saturday morning dwindling to 20 to 30% chance over central Iowa Saturday morning through Sunday morning. A break in the rainfall will arrive as another shortwave trough lifting northeastward or eastward moves through the region. This should bring large scale subsidence into the area on Sunday providing drier conditions that may last into at least Monday. Temperatures late this week into early this weekend will remain on the cool side.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1202 PM CDT Tue Sep 22 2026

Widespread clouds with IFR and low end MVFR ceilings will be common through this afternoon, but ceilings will trend upward tonight with VFR conditions expected over the eastern terminals this evening and the western terminals by around midnight. Drizzle and/or patchy fog this afternoon is expected to dissipate through the afternoon; however, it is possible light fog may try to develop toward sunrise. Confidence is low in this potential so it is not included at this time. Further, may see scattered cumulus clouds developing by the end of the period over the eastern terminals due to lingering low level moisture, which is shown by the FEW025-FEW040 ceilings.

DMX WATCHES/WARNINGS/ADVISORIES

None.