textproduct: Des Moines

KEY MESSAGES

- Dry conditions prevail through Monday night with highs in the low and middle 80s. High level smoke aloft continues.

- Up to 40% chance of patchy fog Monday morning.

- Widespread thunderstorm chances return Tuesday through Wednesday bringing welcome rainfall for many. Will need to monitor if rainfall repeats over the same area. A few storms may be strong to perhaps severe.

SHORT TERM /THROUGH MONDAY NIGHT/

Issued at 153 AM CDT Sun Aug 2 2026

It is a tranquil weather night over the state with a just a few clouds over eastern Iowa flying southwestward around the continuing to depart low pressure, which is over the lower Ohio Valley. Upper level water vapor imagery from GOES-East shows a wound up, positively tilted trough in the vicinity of the low while upstream ridging begins to tilt towards the region. Flow throughout the atmosphere over Iowa is from the north or northeast with a zone of high pressure pushing into the state. This airmass is dry and will foster a day with abundant sunshine, though scattered diurnally driven cumulus may pop over eastern Iowa due to the closer proximity to the low's wraparound moisture. One challenge to the forecast are the dewpoints with the initial National Blend of Models suffering from a seasonal high bias in this drier regime. However, this is also peak evapotranspiration season, which may offset some of the lower guidance. Forecast soundings from a variety of models (e.g. NAM, GFS, HRRR, RAP, NAMNest) show the boundary layer becoming well mixed entraining drier air to the surface late in the morning to early evening. While the middle and upper 50 dewpoints some models produce seems out of reach, have backed off dewpoints a few degrees to the low and middle 60s today. Temperature wise, conditions will be seasonal in the low 80s.

As high pressure moves off to the east tonight, light winds and a clear sky offer a setup for fog potential. LAMP probabilities are around 20 to 30% areawide while HREF is between 20 and 40%. Any patchy fog early Monday will dissipate after sunrise with another mostly sunny day forecast. While dewpoints Monday were once again adjusted downward with similar thinking as above, they will be higher than Sunday in the middle and upper 60s due to southerly flow ahead of the advancing trough and cold front that will be moving over the northern states towards Iowa.

For both today and Monday, high level smoke will continue to be aloft with the HRRR and RAP showing this through their entire runs ending Monday with the RRFS showing it through Tuesday ahead of the nearing cold front.

LONG TERM /TUESDAY THROUGH SATURDAY/

Issued at 244 PM CDT Sat Aug 1 2026

A segment of the upper low in Canada will intensify along the national border and tilt negatively across North Dakota and Minnesota. We'll see the effects of its cold front as early as Tuesday afternoon, lasting through Wednesday. Instability over 1000 J/kg sets up in the warm sector, but with favorable deep-layer shear lagging behind the boundary. Flow will be parallel to the boundary and PWATs will rise above 1.5", so there will be heavy rain potential in northern Iowa due to moisture content and training storms. This risk is currently represented with a Marginal Excessive Rainfall Outlook.

Iowa will stay in cyclonic flow through the remainder of the week which will keep precipitation chances and cooler temperatures in play.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1043 PM CDT Sat Aug 1 2026

VFR conditions overnight with a few passing clouds over the east. The wind will be light from the north to northwest. There is a low chance of fog tonight but did not include in this forecast due to the low probabilities. Scattered cumulus is possible on Sunday with bases in the 3-4kft range. The wind will become more northeasterly through the day but sustained wind speeds will remain mainly below 12 kts.

DMX WATCHES/WARNINGS/ADVISORIES

None.