textproduct: Des Moines

KEY MESSAGES

- Drizzle and fog this morning will gradually diminish from northwest to southeast through the day today.

- Sunny and cool Wednesday for the first day of fall.

- Cooler temperatures in the 60s to finish the week with rain returning Thursday and lasting into the weekend.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 228 AM CDT Tue Sep 22 2026

High pressure sits across the Great Lakes early with morning with easterly wind across the state, helping to entrain some of the drier are from the high into parts of northeast Iowa. Meanwhile, GOES water vapor shows two embedded shortwaves rotating across Iowa on the periphery of the high to the east. The leading shortwave is pushing across eastern Iowa and pulling the deeper saturation with it. Light showers continue across eastern portions of Iowa while shallower moisture in central Iowa has allowed for a shift to patchy fog and drizzle. The second embedded shortwave will push across Iowa today and bring with it drier air, noted in the water vapor imagery this morning across South Dakota. As this pivots across the area soundings dry out and that lingering patchy fog and drizzle will diminish from northwest to southeast through the day today. Dewpoints fall to the 40s and low 50s across the state. With less moisture in place the cloud deck should lessen and light wind will limit any mixing, allowing temperatures overnight to fall to near those dewpoints. If conditions come together enough (diminishing cloud cover, light winds, lingering low level moisture) then fog will be possible into Wednesday morning. Current thinking is that some cloud cover will linger overnight and and winds may be just enough to prevent more widespread fog development, limiting it to low lying areas.

The southern US ridge pushes north into the area on Wednesday, maintaining dry and clearing conditions across the state. Soundings continue to dry through the day and expect increasing sun through the day. After the persistent rainy period, sunshine on the first day of fall will be welcome.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 151 PM CDT Mon Sep 21 2026

The ridge axis that nosed up into the north central US will be pinched off as shortwave energy starts to flow into the region. These pieces of energy will be coupled with waves of low level thermal lift, weak to modest QG convergence surges, and a nocturnal low level jet pointed into eastern Nebraska or Iowa from Thursday into at least Saturday. All these factors point to an active period of wet conditions featuring showers and occasional storms with short spans of dry conditions. Atmospheric moisture will also tick upward from Thursday with precipitable water values back above 1.5 inches, which will be more common than not through Saturday evening. While warm cloud depths and precipitable water values will not be as high as last week, they will still be well above normal for the latter part of September and favor efficient rainfall production and slow movement given the 850-300mb flow between 20 and 30 knots. Rainfall totals from the global models are not eye popping at 1 to 3 inches Thursday through Sunday morning with ensemble probabilities less than 20% for 1" of rainfall in a 24 hour period. However, given antecedent wet conditions (National Water Model analysis showing 60% or higher soil moisture, NASA SPoRT top 4" and 16" showing 70th percentile or high soil moisture south of Iowa 3) and elevated streamflows in all but the upper Iowa River basin and the upper forks of the Des Moines River, will need to monitor rainfall trends for any flash flooding or additional rivers rises later this week into the weekend. Lapse rates during this period will be weak and any amount of instability and favorable shear do not overlap temporally so while there could be a few strong storms, no widespread severe weather is foreseen. This is further supported by AI/ML guidance, which is not pinging on anything late this week and weekend.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 625 AM CDT Tue Sep 22 2026

Low stratus and patchy fog and drizzle is resulting in IFR to LIFR conditions across Iowa impacting all sites (except KMCW). Visibility will begin to improve after 18z with ceilings lifting slowly from 00-06z. After 06z conditions begin to improve to VFR across all sites.

DMX WATCHES/WARNINGS/ADVISORIES

None.