textproduct: Des Moines

KEY MESSAGES

- An Enhanced (Level 3 of 5) Risk for severe thunderstorms continues across northern Iowa this morning followed by a Slight (Level 2 of 5) Risk (after 7am/12z Tue). Damaging wind gusts are the primary threat with isolated large hail and locally heavy rainfall possible.

- Smoke aloft and hot, humid conditions across southern and portions of central Iowa continue through Wednesday, with heat indices at or just above 100 degrees possible.

- Another potential window for severe weather returns tonight into early Wednesday. Shower and thunderstorm chances continue through the week with severe weather and heavy rain possible at times.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 233 AM CDT Tue Aug 11 2026

Another night with continued storm chances with moderate uncertainty continues. This morning, the MCS which was originally forecast to form and move across the Dakotas has not yet formed and guidance is now split on the potential scenarios as we move into this morning. At a first glance, radar and some of the previous solutions in the convective allowing models (CAMs), there is a possibility for ongoing storms in north central Nebraska to hit the Low Level Jet (LLJ), merge with the ongoing messy cluster in southeastern South Dakota, and barrel across northern Iowa over the next several hours. This solutions appears unlikely at the moment, as the cluster of storms in Nebraska is currently trending down. Part of the difficulty is that the disorganized cluster in southeastern South Dakota has not been captured by models, safe for the 06z WoFS run. If the 06z WoFS run is to be believed, this cluster will make its way across Iowa ahead of potential development farther northwest in South Dakota. This potential development, aided by the LLJ, will quickly organize into an MCS and move across northern Iowa through the morning.

Whether anything can grow upscale into an MCS and whether an MCS can sustain itself across northern IA this morning remains to be seen, as this is highly dependent on the LLJ and its strength. Deterministic guidance has backed off on the magnitude of the LLJ, while the NAM remains persistent that a strong (~50kt) jet will set up and be pointed into Iowa around 09z. If a stronger jet has formed and is pointed into Iowa, storms will be in an unstable and highly sheared environment, and a damaging wind threat will remain through the morning hours today. If a stronger jet hasn't formed or is not favorably oriented, thunderstorms across the northern half of the state would be weaker to marginally severe.

The rest of today looks to be dry, hot, and humid again. Heat will be felt the most across southern and portions of central Iowa, where highs are once again forecast to be in the low to even mid 90s and heat indices could ever so slightly exceed 100 degrees in spots. While not as dense, smoke overhead will dampen heat from being more extreme and reaching advisory criteria. That said, a few observations could reach advisory level, but not anticipating widespread heat indices over 105. For now, a Heat Advisory was not issued but trends will be monitored through the morning. If overnight showers and storms do not occur in portions of southern Iowa, heating could begin earlier and this will need to be reevaluated. Going further with the enhanced heat and humidity, warm 700mb temperatures will once again hinder any convection during the daytime hours despite ample instability and shear across the state.

Attention then gets turned toward the overnight hours tonight into Wednesday. The potential exists for another MCS to form and move across the state. Solutions at this point are still highly varied. More questions about the LLJ and its strength, orientation, and position come up. For now, the GFS shows the most robust LLJ at 4am/09z Wednesday, while the NAM and Euro are less favorable. Much like tonight, the atmosphere will still be unstable and highly sheared. In CAM land, solutions where an MCS is not realized instead points to the potential for early-morning convection to form along a boundary. If this is the case, initiation will be much earlier than 'normal,' beginning in the hours just after sunrise rather than in the afternoon with better diurnal heating.

Once again on Wednesday, hot and humid conditions are expected across southern and portions of central Iowa with heat indices nearing or barely exceeding 100 degrees possible. Shower and thunderstorm chances will return again after sunset.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 307 PM CDT Mon Aug 10 2026

Most of Wednesday morning will be dry but we are watching the potential for showers and storms Wednesday afternoon into Thursday. Medium range guidance look to bring ample moisture in and with PWATs over 2", heavy rainfall could occur.. Excessive Rainfall Outlooks has central Iowa in a Slight Risk for flash flooding. Embedded shortwaves look to track across the Plains and into central Iowa keeping us active with showers/storms through the end of the week.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1057 PM CDT Mon Aug 10 2026

Scattered to broken MVFR clouds are in place across northern Iowa, but have generally remained scattered/VFR. This is expected to continue into the night before showers and storms increase across the area through the morning. Storm trends remain relatively uncertain, with timing slowing down some since last issuance. The most likely locations to be impacted are still KFOD, KMCW and KALO, with a lower chance for a few showers or storms near KDSM. Strong winds may accompany these storms, but these will depend on the evolution of the complex through the morning, so will monitor and amend accordingly. LLWS also develops for a few hours south of where storms are expected, including KDSM and KOTM. Of note, should storms not come to fruition, patchy fog could develop across northern Iowa, but any thunderstorm activity will negate this.

Once storms move out today, VFR conditions develop with light and somewhat variable winds through the day.

DMX WATCHES/WARNINGS/ADVISORIES

None.