textproduct: Des Moines

KEY MESSAGES

- Ongoing thunderstorms across northern/northwestern Iowa early this morning will carry a slowly diminishing severe weather threat. Additional thunderstorms are then forecast across roughly the northwestern half of Iowa Wednesday night and Thursday morning, with a low severe weather threat.

- Heat and humidity will persist especially across southern and southeastern Iowa, where a Heat Advisory remains in effect through Thursday afternoon. Heat index values will peak near 100 degrees each day.

- Additional heat and storm chances continue through the end of the week into Labor Day weekend.

SHORT TERM /THROUGH THURSDAY/

Issued at 117 AM CDT Wed Sep 2 2026

A large 500 MB ridge lies just to our southeast, smothering much of the country in a heat wave that has already affected parts of Iowa for the last few days. Meanwhile, weak ridging extends up the High Plains, but is being penetrated and flattened by a couple of subtle shortwave impulses. At the surface, a weak trough extends from the lee of the Colorado Rockies northeastward to near the South Dakota/Iowa/Minnesota intersection. This is providing a focus mechanism for vigorous thunderstorm development at the current time, which is being aided by one of the aforementioned 500 MB impulses as well as a gradually strengthening nocturnal low-level jet. As the impulse continues to track eastward away from our area, the storms will likely linger in our northern and northwestern counties overnight but with gradually diminishing intensity. Severe weather remains possible for several hours before that occurs, and a Severe Thunderstorm Watch remains in effect until 5 AM accordingly. It is likely that at least isolated showers and thunderstorms will continue dribbling near the boundary after sunrise today, but as the low-level jet fades out later this morning and warmer air aloft rebuilds into the area with the expanding ridge, lingering activity should be increasingly suppressed and have largely removed rain chances from the forecast for this afternoon and evening.

The next 500 MB shortwave will overtop the ridge in the High Plains later today, in what will be somewhat of a repeat of what has occurred in the last several hours. Thunderstorms will once again generate somewhere near the Nebraska/South Dakota border this evening, then track roughly eastward toward southern Minnesota and northern Iowa into Thursday morning before fading out again. However, with this second round the shortwave appears weaker and forcing for ascent is more modest. Also, the low- level jet Wednesday night will be oriented somewhat more to our west rather than pivoting directly overhead. The combination of these effects is a reduced severe weather threat during this time, however, given the instability aloft and generally favorable deep-layer shear profiles, a couple of strong to severe storms cannot be ruled out.

Aside from thunderstorm and severe weather chances the next couple of days, the other primary weather impact is a continuation of heat and humidity that really ramped up on Tuesday. Given our continuing proximity to the large heat dome over the Ohio/Mississippi River valleys, little relief from the heat is anticipated through Thursday - at least in the southern half or so of Iowa. In northern Iowa, lingering cold pool and convective cloud debris effects should blunt the heat somewhat, with highs more in the mid to upper 80s in that area. Farther south however, heat index values are still expected to peak near 100 degrees each day with little overnight relief, and the Heat Advisory remains in effect through Thursday.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Issued at 300 PM CDT Tue Sep 1 2026

As we head into the end of the work week and Labor Day weekend, additional showers and storms will be possible again Thursday night into Friday morning. Highs on Friday will once again climb into the lower 90s, coupled with oppressive dew points in the 70s. The ongoing Heat Advisory may eventually need to be extended through Friday. However, we opted to hold off on any extensions with this forecast package due to lingering uncertainty regarding the southward extent of Friday morning convection. Additional showers and thunderstorms chances will remain in the forecast through the weekend, alongside continued warm highs in the upper 80s and lower 90s.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 627 AM CDT Wed Sep 2 2026

VFR conditions will prevail through the TAF period. A few thunderstorms will be present early this morning and may briefly effect MCW, but otherwise coverage and probability will be too low for TAF inclusion today. Overnight, toward the end of the 12Z TAF period, additional showers and storms are expected and higher probabilities at the northern terminals support PROB30 groups there after around 09Z. Aside from SHRA/TSRA effects, no low ceilings or reduced visibilities are expected.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory from 1 PM this afternoon to 7 PM CDT Thursday for IAZ057-058-070-071-081-092.

Heat Advisory until 7 PM CDT Thursday for IAZ059>062-072>075- 082>086-093>097.