textproduct: Des Moines

KEY MESSAGES

- Patchy fog expected to increase this morning over portions of southern to central Iowa. Weakening storms are also possible near sunrise in northern Iowa.

- Warmer temperatures in the upper 80s and 90s on Wednesday, with thunderstorm and heavy rain chances returning Wednesday night into Thursday and potentially Friday.

- Warmer and drier conditions develop late this weekend into early next week.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 300 AM CDT Tue Jul 7 2026

Conditions across Iowa early this morning remain dry, though further north, a surface boundary currently draped across southern Minnesota has a weakening line of showers and thunderstorms that are slowly tracking southeast through the state. While most of this activity is weakening, one cluster on the western fringe of this boundary is still carrying alot of lightning, with other storms further east are quite weak in nature. The overall expectation remains the same that these storms will continue to weaken and eventually dissipate as they track further southeast, given weak high pressure overhead and drier air. Most guidance has this activity dying off before reaching Iowa, though given slower weakening trends, the potential has increased for at least portions of far northern Iowa to see at least light rain and weak storms near sunrise before drying out closer to mid-morning, if not sooner. Therefore have added low PoP mentions (10-20%) in these areas to reflect current trends. Otherwise, starting to see a few sites experience slightly lowered visibilities between 3-7 miles over portions of central to south central Iowa due to patchy fog development. Given clear skies across these areas and very light to calm winds at the time of this writing, the expectation remains for patchy and localized dense fog to increase in coverage over the next 3-4 hours, before dissipating. The cloud shield just starting to reach into northern Iowa though will likely expand further south with time this morning, which could put a damper on fog potential. There is some uncertainty in how far south exactly these clouds will extend, but have at least increased cloud cover over northern into portions of central Iowa into mid morning.

Upper level ridging over the Upper Midwest, paired with weak high pressure extending westward into Iowa yet will keep conditions on the dry side across much of the area today, with surface winds shifting south/southwesterly, bringing in slightly warmer air as temperatures reach into the mid to upper 80s. Surface cyclogenesis on the lee side of the Rockies late this afternoon to evening per guidance is expected to occur, with a warm frontal boundary over South Dakota into Minnesota, placing Iowa in the warm sector. Given the overall setup, any shower and storm development is expected to be in close proximity to the boundary north/northwest of Iowa, which will be the focus for the next chance of showers and storms into the state by Wednesday afternoon to evening as this boundary is shunted south and east. A Slight Risk per SPC now exists for potential severe weather into northeast Iowa during this time frame. More details regarding this activity is in the long term discussion below.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 245 PM CDT Mon Jul 6 2026

The upper level wave to our south and surface high overhead will begin to depart eastward on Tuesday, bringing southerly return flow back up into Iowa Tuesday night through Wednesday. The result will first be warmer temperatures with highs in the upper 80s to low 90s on Wednesday. The upper level pattern will begin to transition to more zonal flow through this same period and the boundary to our northwest will begin to sink south and east towards the state. Weak energy working through the zonal flow will develop shower and thunderstorm chances along said boundary starting late Wednesday and lasting intermittently over Iowa into Thursday morning. Plenty of moisture (2"+ precipitable water values) and instability (~1500 to 2500+ J/kg of MUCAPE) will be present over Iowa during this same time, although shear will be minimal (20 to 30 kts of 0-6 km shear), suggesting updrafts may struggle to become organized. Likewise, while there does appear to be weak energy moving through the zonal flow, the forcing is unimpressive for most of the area, barring southwest Iowa where the low level jet is expected to nose into overnight. This jet could provide some extra lift for storms through central and southern Iowa Wednesday night into Thursday, but other areas may need a bit more juice to kick things off. Therefore, the main concern at this time is the potential for heavy rainfall fueled by this low level jet. See hydro discussion below.

The pattern remains active through the end of the week, with another shortwave slated to move through the midwest Friday, albeit with more uncertainty on exact track and evolution. However, by this weekend models show good consensus of a broad upper level ridge spanning much of the western and central US. This regime would lend itself to warmer temperatures and drier conditions for Iowa late this weekend and into early next week.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1046 PM CDT Mon Jul 6 2026

Trended more aggressive for fog this issuance as cloud cover will be delayed in reaching most TAF sites. Confidence has increased in river valley fog at KFOD due to less clouds and have reflected transient LIFR conditions typically seen there. KDSM will have a short window of MVFR vsbys from fog. Highest confidence in fog will be at KALO and KOTM with IFR vsbys possible within 2 hours of sunrise.

HYDROLOGY

Issued at 245 PM CDT Mon Jul 6 2026

Rivers and streams in central Iowa continue to see increased flow as water from the heavy rains late last week and this weekend continues to route through the system. Two rivers in central Iowa maintain flood warnings at this time. The first is the South Skunk River near Colfax (CFXI4) which is actively cresting at moderate flood stage and expected to fall below flood stage tomorrow. This portion of the South Skunk River flows into the Oskaloosa (OOAI4) area, but this point should remain below it's minor flood stage. The Iowa River near Tama (TMAI4) also maintains a flood warning as it continues to slowly rise, with an expected to crest at or just below minor flood stage today. Other rivers within the Des Moines and Cedar River basins are also at increased levels as water works it's way down stream, albeit all below flood stage and continuing to recede.

Additional rainfall later this week, especially Wednesday evening through Friday, could lead to slower improvement and/or additional rises on area rivers, depending on what basins this rain affects. The exact corridor of the heaviest rain is still uncertain, but will be monitoring closely through the coming days.

DMX WATCHES/WARNINGS/ADVISORIES

None.