textproduct: Des Moines

KEY MESSAGES

- A few thunderstorms possible again tonight, mainly over southern Iowa. Severe weather and heavy rain potential looks low at this time.

- On and off thunderstorm chances through most of the upcoming week.

- Warm and humid conditions Monday through Wednesday with heat indices near 100 at times over central and southern Iowa.

- Wildfire smoke will likely be over Iowa through Wednesday.

SHORT TERM /THROUGH MONDAY/

Issued at 206 PM CDT Sun Aug 9 2026

An outflow boundary from the morning thunderstorms is stretched from far southeast Iowa to just south of the Des Moines metro to near Denison. This has created a pseudo warm front with breezy southerly winds over south central Iowa. The 18z SPC MesoAnalysis is suggestion 4000 J/kg of uncapped CAPE over south central Iowa. This is way overexaggerated with a stout elevated mixed layer (EML) capping over the area. MLCAPE values are much more realistic with 150-200 J/kg of CIN. This capping will prevent any surface based thunderstorm development for the rest of the day.

The low level jet (LLJ) will intensify again to 50+ kts tonight and point into southern and central Iowa after midnight. A ribbon of MUCAPES over 3000 J/kg does develop along the nose of the LLJ. Similar to the daytime now, much of that instability will not be realized, for a different reason. Utilizing the 850-300 mb MUCAPE is lifting the parcel from 850 mb. The EML will be situated just above this lifted parcel and will prevent ascent. While there is some saturation of the EML overnight with the moisture transport, it does not appear to be enough saturation to overcome this capping. Much like last night, any storms will have to be rooted above the EML and in this case with less MUCAPE available. Much of Monday will be dry outside of any lingering morning convection as the EML again reintensify.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

Issued at 206 PM CDT Sun Aug 9 2026

Little change in the upper level pattern as westerlies aloft prevail through at least mid-week before a trough develops over the Western CONUS leading to weak ridging into Iowa. Expect wildfire smoke to persist over Iowa until the trough develops to the west and changes the source region of the upper flow. This smoke remains dense enough for solar filtering and perhaps will result in slightly cooler temperatures than forecast. The little change in the pattern will also keep the surface boundary in the vicinity of Iowa through Wednesday then it will shift a bit south into Missouri. On and off chances for thunderstorms will occur during this period, especially during the overnight hours as the LLJ fuels thunderstorm development in addition to the periodic short wave passages. Thunderstorm chances will continue to end the week despite the arrival of cooler air as an overrunning event of the surface boundary appears possible. Heat index values may eclipse 100 degrees Tuesday and Wednesday over central and southern Iowa but at this time, should remain below headline criteria.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1240 PM CDT Sun Aug 9 2026

An outflow boundary that moved through central Iowa this morning remains stretched over south central Iowa and this has brought a change to wind directions and breezy conditions in vicinity of the boundary. The outflow boundary will washout this afternoon with the wind becoming southerly at KDSM/KOTM and at other sites later in the period. There remains a low chance for fog overnight and have included mention at KMCW, where the greatest potential for fog exists. Scattered thunderstorms are possible late tonight, mainly over southern Iowa including KOTM.

DMX WATCHES/WARNINGS/ADVISORIES

None.