textproduct: Des Moines

KEY MESSAGES

- Isolated areas of patchy fog expected this morning.

- On and off showers and storms expected over western/southwestern half of Iowa later this morning through Monday morning. Gusty winds and heavy rain are the primary hazards of concern.

- Additional storm chances with a passing boundary late Monday through Tuesday, with some potential for severe weather over much of the forecast area.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 304 AM CDT Sun Sep 6 2026

Relatively quiet weather is ongoing early this morning, with mostly clear skies overhead. Due to light winds and little difference in temperature/dewpoint values in the 70s making for continued uncomfortable nighttime conditions, isolated areas of patchy fog have developed over portions of northern and eastern Iowa, where lowest visibilities are around 3-4 miles. The expectation is that little change in conditions should allow for some expansion of this patchy fog coverage, mainly over northern and eastern Iowa, before dissipating around/just after sunrise.

As fog dissipates around sunrise, a mid-level shortwave rounding the apex of the persistent ridge overhead will allow for increased forcing for lift into Iowa. This feature will interact with a noteworthy instability gradient that is draped over the west/southwest half of Iowa, which will be the focus area for showers and storms to develop. While CAM guidance varies somewhat in the evolution and timing of this expected convection, probabilities are looking highest for storm development and increased coverage over western/southwestern Iowa into the afternoon to early evening, tracking southeastward with time. The environment overhead features MUCAPE values around 2000-3000 J/kg, given higher moisture content and temperatures into the mid to upper 80s, while lapse rates look unimpressive around 6.5 C/km paired with shear values around 25 knots. While isolated in nature, there is a potential for strong to severe storms at times with this on and off storm activity, with highest chances in the afternoon to evening. Gusty winds would be the main hazard of concern, with DCAPE values around 1000-1500 J/kg. The signal is also increased for heavy rain with this activity, given higher PWATS around 2 inches, warm cloud depths, and a skinny CAPE profile. This shower and storm activity looks to decrease in coverage into the evening, but could continue at times into Monday morning given an increasing LLJ extending into far western Iowa. Some model members suggest a decaying MCS dropping southward across western Minnesota through the morning, but looks to dissipate before reaching NW Iowa. This however will be something to keep an eye on. Total rainfall amounts around an inch look to be common by Monday morning near and west of I-35, though localized 2-3 inch amounts are certainly possible. Flooding concerns should be minimal, with any potential mainly over urban areas if rainfall can quickly accumulate.

Throughout the rest of Monday, the aforementioned ridge will translate further eastward, with its location now more directly over Iowa. This will allow for an increase in 850mb temperatures overhead and therefore capping, as well as a lack of instability due to the influence of the surface high over the Great Lakes to cut off any additional shower and storm development. Dry conditions should be common across the forecast area by the afternoon, with increasing low level southwesterly flow allowing for breezy conditions, as gusts up to 25-35 mph are expected, highest over northern Iowa. Cloud cover will decrease at the same time, with forecast highs through the 80s, warmest southwest.

By Monday evening, the ridge breaks down somewhat as a rather potent trough and associated deepening surface low tracks eastward into Manitoba. With this system, an attendant cold front extending down into the Central Plains is forecast to enter northwest Iowa late Monday evening into Tuesday morning, which will be the next focus area for shower and storm activity to occur. At this time, deterministic models suggest the development of showers and storms to occur across northern Iowa through Tuesday morning, as an increasing LLJ northward across Iowa will act to enhance lift along the boundary, with notable warm air advection overhead. This activity may wane a bit later in the morning with the decreasing jet, but is suggested to develop additional convection later in the afternoon to evening given peak heating and the gradual resurgence of the LLJ late in the day further south. The airmass ahead of this feature will be quite warm and humid, with temperatures expected to top out through the 90s, paired with dewpoints in the upper 60s to low 70s. This is an ideal setup for storms to become organized and potentially turn strong to severe, with a Marginal Risk in place over much of the forecast area per latest SPC guidance. Heavy rain with this activity is also looking increasingly likely, given strong moisture transport into Iowa. Additional details will be refined on specific timing and coverage in future forecast updates. Forecast heat indices back into the 100-105 range over portions of central to southern Iowa before storms arrive will likely lead to additional heat headlines in the near future, so stay tuned.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Issued at 239 PM CDT Sat Sep 5 2026

The flattening of the sub-tropical high will continue Wednesday with a westerly/zonal flow for the mid to end of the week. Less certainty late next week with spatial and temporal differences with the next strong upper level short wave that will arrive into the Pacific Northwest. This will determine how much the sub-tropical high ridging can become re-established over the western CONUS and the difference between seasonal westerly flow or cooler northwest flow and attendant precipitation chances associated with each.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 633 AM CDT Sun Sep 6 2026

Seeing patchy areas of low ceilings and fog across the majority of terminals, leading to anywhere from MVFR to LIFR conditions this morning. Conditions will slowly improve over the next 2-4 hours or so across all sites as ceilings lift and fog dissipates. Otherwise, there remains the potential for on and off showers and thunderstorms to impact KFOD after 16z, and later this afternoon at KDSM as coverage of this activity increases. However, confidence on exact coverage and timing remains low-end, so have kept PROB30 mentions at this time and will amend as needed as showers and storms develop through the day. Winds out of the southeast will increase, with gusts up to 15-20 mph by the afternoon.

DMX WATCHES/WARNINGS/ADVISORIES

None.