textproduct: Des Moines

KEY MESSAGES

- Hot and humid conditions continue today and tomorrow with heat indices in the upper 90s to near 100.

- Multiple rounds of storms this afternoon through the overnight, mainly over north central Iowa. A few severe storms are possible, with wind, hail and heavy rain the primary risks.

- Hot and humid through the end of the week and into the weekend. Storm chances persist, some of which may be severe.

SHORT TERM /THROUGH FRIDAY/

Issued at 257 PM CDT Wed Jul 1 2026

Hot and humid conditions have developed over central and southern Iowa where mostly clear skies have allowed plenty of surface heating. Apparent temperatures as of mid-day are in the mid to upper 90s, with a few locations near or exceeding 100F. Areas farther north and west haven't warmed nearly as much as anticipated due to persistent cloud cover and light rain that still lingers over the area, resulting in temperatures generally in the 70s to low 80s. For this reason, have canceled the Heat Advisory for portions of far northern Iowa. Hot and humid conditions will persist in cloud-free areas this afternoon and early evening, with warm lows in the 70s once again tonight.

We will once again be looking at thunderstorm chances over the area this afternoon through the overnight, thanks to the warm and moist air mass over Iowa. The rain and cloud cover over northern Iowa has mucked up the environment along the boundary some today, resulting in an over-worked and more stable environment across southern Minnesota and far northern Iowa where storms were initially progged to develop. This has led to a difficult forecast for storm initiation this afternoon, as the synoptic boundary is being washed out by the ongoing showers. Most immediately this afternoon, short- range guidance depicts isolated to scattered storms firing along the differential heating boundary in north central to northeast Iowa this afternoon. These storms will have access to a moist and untapped air mass, boasting 3000+ J/kg of mixed layer CAPE and a modest amount (30 to 40kts) of effective shear, supporting organized convection and supercellular storms. Large hail and damaging winds will be the highest probability risks thanks to the supercellular storm mode and 1000+ J/kg of DCAPE. The low level flow isn't super favorable for tornadic development, as winds are generally out of the southwest, but some moderate turning in the low levels (0-3 km SRH of 100 to 200 m2/s2) and a fair amount of low level stretching (0-3 km CAPE of 100+ J/kg) would allow for tornadogenesis to occur, especially in the northeastern portions of the state. Finally, heavy rainfall is also a concern in such a moisture rich environment, but this risk will come more into play with storms expected overnight.

In addition to the storms this afternoon and early evening in north central and northeast Iowa, additional thunderstorm activity is expected along the nose of the low level jet throughout the overnight. These storms will likely be elevated as they occur in a cooler, more worked over airmass. Therefore, severe risks are lower, but do still exist thanks to the plentiful instability and shear in place. Large hail and damaging winds remain concerns overnight, while the tornado risk is very low. Any upscale growth into a mesoscale convective system could lead to a swath of enhanced winds overnight. Low level jet storms training from west to east along a boundary in a 1.8" to 2" PWAT environment also introduces concern for heavy rainfall and flash flooding, especially if it coincides with the same areas where the afternoon convection occurs. Much of northern Iowa has drier soil and maturing corn, which should help mitigate rural flooding concerns, but urban areas are almost always more vulnerable to heavy rainfall. Therefore, widespread flooding is not expected, but multiple rounds of heavy rain in a single basin or over a city/town could lead to isolated flooding concerns.

The overnight storms generally wrap up Thursday morning, with a brief lull expected through mid-day. Hot and humid conditions develop once again on Thursday, especially over central and southern Iowa but convective debris from the overnight activity will keep temperatures relatively cooler for most areas. Heat indices are expected to be in the upper 90s to near 100 at their warmest. That said, we are going on day 5 of the hot and humid conditions, so have maintained the Extreme Heat Warning for areas that will be pushing those 100F heat indices.

Although we get a brief lull from storms on Thursday, it will likely be short-lived as storms are expected to develop once again Thursday afternoon. Of course, there will be no shortage of instability available to storms Thursday and more modest wind shear (right around or below 30 kts of 0-6 km shear). This would at least support an organized updraft, but any more robust coldpools that develop would likely out run the storm. Model guidance indicates storms firing over western Iowa Thursday afternoon and tracking northeast through the night. They also depict some fairly strong winds (70+ mph) thanks to the inverted-v soundings and 1200+ J/kg of downdraft CAPE. This of course assumes skies clear out and boundary layer mixes after the overnight activity. At least scattered showers and storms then continue over the area into Thursday night, although with so many rounds of precipitation prior, it's tough to lock down specific details. What will be something to watch is where all this rain falls, as responses on rivers and/or flash flooding may develop if successive heavy rain occurs over similar areas.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 257 PM CDT Wed Jul 1 2026

As we get into Friday and the holiday weekend, uncertainty increases given so many convective scenarios that will play out prior. However, the upper level pattern will be trending more zonal with continued moisture advection and warm temperatures working up into the state. This pattern will be conducive for continued rain and thunderstorm chances persisting into the weekend and potentially the Independence Day holiday. It seems unlikely the state of Iowa will be completely spared from thunderstorms Friday into Saturday. Therefore, the most important takeaway is to stay tuned to the forecast as it will be evolving into the weekend. The hot and humid temperatures will also persist into Friday and Saturday. Another heat headline may be needed on Friday, but given uncertainty of convective trends through the next 48 hours have decided to hold off during this shift. Independence Day looks a tad cooler, but will also be driven by the persistent thunderstorm chances through the end of the week and into the weekend.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 702 PM CDT Wed Jul 1 2026

Convective timing across northern Iowa stands as the main forecast challenge tonight. While isolated pre-activity is possible, storms are expected to ramp up around 01z. Introduced PROB30 groups at KMCW and KFOD from 01z through the early morning hours to account for this window. Convection moves into KALO around 05Z, with showers reaching KDSM near 08z. Expect most shower and storm activity to taper off near daybreak, with VFR conditions returning to all terminals shortly after.

DMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 10 PM CDT this evening for IAZ026>028. Extreme Heat Warning until 10 PM CDT this evening for IAZ035>039-046>050-058-070-071-081. Extreme Heat Warning until 10 PM CDT Thursday for IAZ059>062- 072>075-082>086-092>097.