textproduct: Des Moines

KEY MESSAGES

- The heatwave continues, with extreme heat running through the 4th of July weekend. The Extreme Heat Warning continues area- wide today.

- Additional daily thunderstorm chances run through the week, with the potential for severe weather today (Marginal/1 of 5), Wednesday (Slight/2 of 5), and Thursday (Slight/2 of 5).

SHORT TERM /THROUGH WEDNESDAY/

Issued at 254 AM CDT Tue Jun 30 2026

In the immediate term this forecast period, a complex of thunderstorms in Nebraska and southeastern South Dakota is making its way to the east/northeast and is expected to clip the northern fringes of the forecast area, which may bring some localized relief to tomorrow's heat. These storms are currently riding a Theta-E gradient which will limit coverage greatly to northwest and north central Iowa. This activity is expected to move through the area in the very early morning hours and exit a couple of hours after sunrise. The primary hazard is damaging winds with D-CAPE values on the order of 1500 J/kg. Mid-level lapse rates of 7-7.5 C/km would be supportive of smaller hail, but this is negated by a high freezing level.

The highest point of confidence going forward in the short term is the ongoing heatwave continuing. The high is still sitting over the Southeastern U.S. This leads to another day of ample southwesterly flow. Highs forecast in the lower to mid 90s. Combined with dewpoints in the upper 60s to the mid 70s across Iowa, heat indices will be hovering in the low 100 degree range. The high isn't expected to go anywhere come Wednesday, although slightly less moisture is fed into the area leading to slightly lower dewpoints and slightly lower heat indices. While we are expected to remain in southwesterly flow, little relief is still expected as overnight lows are still expected to stay in the mid to upper 70s, mainly in areas along and south of I-80. Areas further north may have more overnight relief due to lingering effects of overnight thunderstorms.

Of lower confidence this forecast period is continued low thunderstorm chances as another shortwave is expected to ripple over part of Iowa. There will be plenty of CAPE around with deterministic guidance showing MLCAPE values in the neighborhood of 2500-3000 J/kg across much of the area and mid-level lapse rates as high as 8 C/km will support some level of convection, but weaker shear across Iowa will be the limiting factor. Additional thunderstorm chances exist on Wednesday with a greater severe potential across our CWA.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 256 PM CDT Mon Jun 29 2026

A similar pattern remains in place through Saturday. High pressure to our southeast will keep the heat and humidity in place, especially across the central and southeast part of the state. Heat indices may drop a tad, but the danger may lie more in the continued days of heat, and the lack of overnight relief with lows in the upper 70s. Therefore, the extreme heat warning has been extended for a large part of the state through at least Wednesday with anticipation of possible further extension in the coming days. As has been talked about the last few days, the heat is expected to continue through the 4th of July weekend, where heat indices on the order of 100 are still being forecast. Storm chances will continue each day, particularly in the western and northern part of the state, as the ring of fire pattern continues. The usual pattern will continue to be large instability built up during the day, LLJ surges at night, and initiates storms overnight that attempt to push east through the highly capped environment over our CWA. Though marginal, it is also worth mentioning the excessive rainfall outlooks across Iowa. With large PWAT and storm chances, chances for flash flooding can't be ruled out on any given day. Per the usual for this time of year, these storm chances will be highly uncertain in their exact timing and intensity.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 602 AM CDT Tue Jun 30 2026

VFR conditions are expected at all sites this TAF period. Lingering showers and thunderstorms may cause brief lowered ceilings and gusts around 25kts at KMCW. Otherwise, there are low (<20%) chances for showers and thunderstorms later today. Confidence in location and impacts at any one terminal are too low to mention at this time. Low level wind shear (LLWS) is also a possibility later in this TAF period. At this time, guidance shows that LLWS would be marginal at best across southern terminals. This will be addressed in future TAF periods as guidance becomes more clear.

DMX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 9 PM CDT this evening for IAZ004>006-015-023-024-033-034-044-045-057-070. Extreme Heat Warning until 10 PM CDT Wednesday for IAZ007-016- 017-025>028-035>039-046>050-058>062-071>075-081>086-092>097.