Area Forecast Discussion

KEY MESSAGES

- Scattered showers and storms this afternoon into evening, with more widespread rainfall over central and southern Iowa tonight into early Sunday morning. A few stronger storms could produce strong winds, hail and heavy rainfall.

- Cooler temperatures with light rain and drizzle persists on Sunday.

- Cool temperatures and moist weather persist into Monday, with drier conditions expected Tuesday and Wednesday.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 255 PM CDT Sat Sep 19 2026

This morning's weather was quite reminiscent of yesterday's with stratus and fog impacting much of the area, and lingering overnight showers and storms. The stratus has remained firm across northern Iowa today and will likely stay that way through the evening into tomorrow morning. Patchy fog is still present at a few sites in northern Iowa, but not nearly to the extent it was earlier this morning. In southern and central Iowa, a bit more sunshine is being observed where clouds have cleared out, although isolated showers and occasional storms have persisted. This activity has been heavily localized and transient.

Through the remainder of the afternoon, occasional showers and thunderstorms are expected to bubble along a southwest to northeast oriented boundary drifting southeastward through the area. While there is a modest amount of instability (1500 to 2500 J/kg) ahead of this boundary, convergence is fairly weak and wind fields are meager. Most of the better shear resides behind the boundary with less than 30 kts of effective shear out ahead of it. There is a pocket of 25 to 30 kt shear along the I-80 corridor, coinciding with the nose of the unstable air, which could favor a few stronger storms capable of producing hail or damaging winds this afternoon into the evening.

The aforementioned surface boundary will sag southeastward into the evening, eventually departing the state late tonight. However, a weak low level jet developing overnight will bring moisture and ascent over the sloping air mass. Assisted by lift from a subtle shortwave, this LLJ will bring another surge of showers and thunderstorms tonight (generally around midnight) into early Sunday morning. Storms are expected to track roughly parallel to the boundary across central and south central Iowa, but remain semi- progressive as the wave pushes through. Since this activity will be elevated and behind the surface boundary, it will have excess to the slightly higher shear environment mentioned earlier. However, by this time of night, instability will also be waning. Can't completely rule out a few stronger storms, especially early in the night, but the risk will be diminishing. That said, with storm motions parallel to the boundary and abundant moisture, heavy rainfall will once again be possible. More on the heavy rain and hydrologic concerns in the hydro discussion below.

As we get to sunrise Sunday, the convective activity should be all but moved out, barring any lingering showers or storms along the Iowa/Missouri border. High pressure and cooler temperatures will be filling in with the northerly flow pattern, but will result in widespread stratus and drizzle as a rare easterly low level moisture transport plume keeps the low levels moist. With marginal instability in the layer (less than 500 J/kg) a few convectively driven showers are possible through Sunday as well, but values will be low enough to eliminate any severe weather risks. With cloudy, cool, moist, and drizzly conditions Sunday into Sunday night, the conditions in Iowa will appear more reminiscent of what most of us consider "fall weather".

LONG TERM /MONDAY THROUGH SATURDAY/

Issued at 255 PM CDT Sat Sep 19 2026

The cooler, fall-like conditions continue into Monday and early next week with highs generally only reaching the upper 50s to near 60 both Monday and Tuesday. Our light rain generally continues into Monday, this time with a bit more synoptic support as a an upper level low meanders into Iowa trudging along in the zonal upper level flow. This low hangs out overhead into Tuesday, but begins to bring drier air into the state. Should this pan out as the models suggest, we should finally see a few dry days Tuesday and Wednesday of next week. However, rain chances do look to return to at least western Iowa on Thursday. More details on that in the coming days.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1228 PM CDT Sat Sep 19 2026

LIFR to IFR stratus with fog persist over northern Iowa, while areas central and south have cleared out. A few showers linger over the area, but are sporadic. Expectation is for rain, stratus and fog/drizzle impact to persist in some capacity this TAF period. KFOD and KMCW generally avoid the shower and storm chances overnight, but will be under stratus and fog through most of the period. KALO, KDSM, and KOTM all have shower and storm chances this evening and into the overnight. Tomorrow, stratus fills in over all sites with a potential for drizzle in the morning through at least mid-day.

HYDROLOGY

Issued at 312 PM CDT Sat Sep 19 2026

The moisture rich environment overhead will bring yet another night of heavy rain potential to the state, this time central into southern and eastern Iowa. The weather prediction center has placed a moderate risk (level 3 of 4) for excessive rainfall to our east, while most of the DMX forecast area resides in a slight risk (level 2 of 4) or a marginal risk (level 1 of 4). Most of the precipitation expected tonight will develop with the low level jet oriented roughly parallel to the boundary, supporting some training storms and potential for prolonged moderate to heavy rainfall. However, CAM guidance suggests storms could be fairly progressive, rather than camping over one area for a long period of time. Likewise, HREF for 1" per hour rates are near-zero, likely thanks to the waning instability by the time these storms develop. QPF output generally ranges from 1 to 2" with some pockets getting closer to 3" in a few models. While this could lead to some ponding issues, or even minor flash flooding should one of the 3" bullseyes align with an urban area, have decided to hold off on a Flash Flood Watch at this time. With the low probability for 1" per hour rates and potential progressive nature of the rainfall, confidence isn't high enough at this time.

As for river flooding, heavy rain in Minnesota last night has resulted in responses on rivers upstream from the Cedar River basin. As a result, water routing down through these basins will likely lead to rises into action stage early this week along the Cedar River, specifically ALOI4 and CEDI4. At this time, flooding is not expected and any additional rainfall today and tonight should fall south and east of these rivers basins. However, upstream observations will be monitored closely as water routes into the rivers and information will be provided should anything change.

For tonight, rainfall amounts of 1 to 3" should generally only cause in-bank rises for most rivers. That said, a few rivers are running at elevated levels from rains earlier this week, namely the North River near Norwalk (NRWI4) and Des Moines River at Ottumwa (OTMI4). Should these basins get hit with prolonged heavy rain tonight, additional rises are certainly possible.

DMX WATCHES / WARNINGS / ADVISORIES

None.