textproduct: Des Moines

KEY MESSAGES

- Severe thunderstorms are possible this evening and tonight, with damaging wind gusts as the primary hazard.

- Heavy rainfall is possible with storms tonight, with a slight uptrend in precip totals.

- High pressure is expected to set up over the central U.S. this weekend into next week, bringing much warmer temperatures.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 249 PM CDT Wed Jul 8 2026

Currently, showers and thunderstorms are ongoing across southern Minnesota along a boundary which is expected to push south/southeast through the afternoon and evening. This forecast gets tricky because there are two areas where convection is expected. The first is along the aforementioned boundary across southern MN, and the other is along an area of deep moisture convergence across western Iowa/eastern Nebraska. Other than potential forcing mechanisms, the environment is more or less the same for each area. Shear is somewhat lacking for widespread severe weather, with 0-6km values between 25kts on the low end and 45kts on the high end depending on the model. The most favorable areas for shear are across far northern Iowa and southern Minnesota, with another somewhat favorable area in western Iowa.

The primary hazards with storms today are damaging wind gusts and heavy rain. As for the damaging winds, soundings have the inverted-V shape to them with T/Td spreads at the surface of nearly 20 degrees. D-CAPE values are between 1000 and 1500 J/kg across much of Iowa and guidance shows wind gusts of between 60 and 70mph through the evening. Some potential uncertainty exists with how long storms would remain severe. Weaker shear values may lead to cold pools outrunning storm clusters which leads to a shorter and less widespread severe window. Should this be the case, after thunderstorms mature redevelopment could occur between the outflow boundary and the main cluster. New updrafts in this in between zone would lower the severe wind threat later this evening.

As for heavy rain, PWAT values still remain in the neighborhood of 2". Storms are expected to be somewhat slow-moving today, between 25 and 30mph. Rainfall totals have been trending upward slightly. REFS and HREF values for the 90th percentile are still between 2 and 3 inches in areas of western and northern Iowa. Both are also hinting at a signal for isolated instances of 3-4" or more of rainfall. Mean values from the HREF and REFS are between 1 and 2 inches. Of note, the axis of heaviest rainfall is still being progged away from areas that received heavy rainfall this past weekend.

With regards to the hail and tornado threat for tonight, both are low and very conditional. Hail is a balancing act between high CAPE values (2000-3000 J/kg) and decent lapse rates (7+ C/km) will be fighting a very high melting level and weak shear. The tornado threat is much more conditional and will be very short lived. Overall SRH values are very low across much of the area, and a brief spin-up along the boundary with storm initiation is possible, in addition to a few funnel clouds due to enhanced stretching, although both cases have a low chance of happening.

Overnight, as the cluster to the west grows it is expected to dive south and ride the CAPE gradient. For the most part, this cluster will be limited in its northern and eastern extent through the evening. Some guidance suggests that after sunset, instability is lost and storms across central Iowa aren't able to sustain themselves, limiting the spatial coverage to west-central and southwestern Iowa. The Low Level Jet is expected to kick in sometime around midnight, although it doesn't look like it will have a large impact on any activity this far north. If the LLJ can nose further into Iowa, this would help increase storm coverage into central and south-central Iowa as the cluster moves to the southeast.

Tomorrow will be warm, humid, and largely dry through the day. Highs around the state will range from the mid 80s to potentially the low 90s. Compared to previous forecasts, the LLJ is progged to kick in farther south across Missouri. With the LLJ coming in farther south, some showers and thunderstorms may graze far southern Iowa tomorrow night as opposed to being more widespread across southern Iowa.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 249 PM CDT Wed Jul 8 2026

Another 500mb shortwave is progged to pass over Iowa Friday before a high sets up this weekend pancakes much of the central U.S. Monday. Once the high sets up, an increase in temperatures is expected with highs making a run for the 90s through the early part of the week.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 643 PM CDT Wed Jul 8 2026

Scattered thunderstorms moving across Iowa are the primary aviation highlight this period. Thunderstorms will move from north to south with some redevelopment occurring behind the current activity. Covered storm chances at all sites though KOTM will be later and diminished. MVFR cigs and vsbys are expected with any thunderstorms. MVFR cigs may linger behind the activity, especially over northern Iowa followed by scattering Thursday afternoon. Outflow wind gusts from variable directions is also possible. Otherwise wind will become light overnight then southwesterly on Thursday.

HYDROLOGY

Issued at 251 PM CDT Wed Jul 8 2026

Area rivers and streams that peaked earlier this week after the heavy rain late last week into the weekend continue to recede but many in the Cedar and Des Moines basins remain elevated, some close to action stage. 3 hour flash flood guidance in much of northern to central Iowa is only 2-2.5" with much higher amounts in western and southern Iowa. This is largely due to the footprint of where the heavy rain has occurred most recently. Similarly, NASA SPoRT 10 cm soil moisture remains elevated near the Hwy 20-Hwy 30 corridors. Some inconsistencies remain in models on how widespread storms will be through portions of central Iowa with greater confidence in the far north/northeast and in the west/southwest. Despite this, it may not take much rain to renew flooding in locations that have recently experienced flooding so issued a Flood Watch for those areas, and in locations in northeast Iowa where model QPF is highest with HREF PMM data suggesting 2-3", localized 4". These QPF totals are also seen in portions of western Iowa, but as previously noted, flash flood guidance is much higher in these areas. In terms of the environment, Pwats top out around 2" near and along the boundary as it moves southward through the night. These are combined with more than sufficient warm cloud depths. Storm motions aren't overly slow, but repeated rounds of rain may still occur as additional storms form on the outflow from initial storms.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Thursday morning for IAZ006-007-016-017- 025>028-036>039-047>050-059>061.