textproduct: Des Moines

KEY MESSAGES

- Very warm today, then storms developing early evening in western Iowa. These will move across Iowa through the evening and late night. Large hail is the initial threat, transitioning to a wind threat late. There is an Enhanced Risk (level 3 of 5) for severe storms today/tonight.

- Severe weather chances are forecast each day from today through at least Tuesday of next week over parts of Iowa. This is a good time to revisit preparedness plans and monitor the forecast closely for updates! Storm chances each day will influence the evolution for the next day.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 325 AM CDT Fri May 15 2026

The low level jet early this morning has pushed across Missouri and into southeast Iowa. Showers and a few thunderstorms have developed on the nose of the jet along a plume of increasing moisture transport into the area. We can pick out this feature on GOES-east water vapor imagery with the larger upper level low swirling to the north and trailing boundary connected to another surface low centered across southwest Kansas. The orientation of surface features should preclude any further development in southeast Iowa early this morning.

Increasingly southerly flow today will send temperatures into the mid to upper 80s with some locations making at run at 90 degrees. Moisture also increases as the pool of 60+ degree dewpoints in eastern Kansas and Missouri will advect into Iowa by this afternoon. This will create an unstable environment with MLCAPE of 2000-2500+ J/kg in place along with 0-6 km shear of 40-50+ kts. The profiles cool well with height, creating 7-8 C/km lapse rates through the mid levels. As the northern surface low pushes east storms are expected to develop along the attendant surface boundary in northwest Iowa in the late afternoon/early evening. Initial discrete storms will be capable of large hail and damaging winds with 150 m2/s2 SRH and steep lapse rates to maintain rotating updrafts. Lack of stretching in the low levels should preclude tornadic development. Storms grow upscale through the evening with an increasing damaging wind threat if storms are able to organize into a bowing line with 1000-1500 J/kg DCAPE. SPC has introduced an Enhanced (level 3 of 5) Risk across northern Iowa to account for this. There is still some uncertainty in when exactly initiation will occur. While 00z CAMs were in good agreement with initiation in northwest Iowa around 21-00z, 06z guidance (especially the 06z HRRR) suggests initiation closer to 00z and in central Iowa, growing upscale east. Storms are anticipated to clear the area by around 07-09z early Saturday morning.

A surface boundary will linger across southern Iowa on Saturday with the other surface low lingering to the southwest across the central plains. MLCAPE of 2000-2500 J/kg will be in place in the warm sector across southern Iowa into Missouri. Storms develop along the boundary as the low level jet increases into it Saturday night. Hazards across Iowa will depend on where this boundary sets up after the storms on Friday night. Slow storm motions are expected across Iowa along the nearly stationary boundary. Additionally, higher PWATs of around 1.5" are forecast. As outlined below, with very dry conditions the last 2+ weeks this moisture should not pose a hydrologic risk and would be welcome.

LONG TERM /SUNDAY THROUGH THURSDAY/

Issued at 157 PM CDT Thu May 14 2026

While temperatures everywhere will be in the 80s, dewpoints well into the 50s and low 60s will pool south of the boundary from storms Friday night. Instability will build beneath an elevated inversion, which should inhibit storm development until later if not late in the afternoon as waves of weak to modest theta- e advection move overhead. Mixed layer CAPE values over 2000 J/kg, around 30 knots or a bit above for deep layer shear, steep mid- level lapse rates, and low level curvature in the hodographs point to severe storm potential. Any storms that can develop in the late afternoon or evening may become strong with large hail and damaging wind gusts the main hazards. In addition, storm motions as low as 10 mph up to around 25 mph may result in locally heavy rain swaths. However, any flash flood threat will be relegated to an urban area due to 0-10cm and 0-40cm NASA SPoRT soil moisture no higher than the 20th percentile and generally less than the 10th percentile. Therefore, there should be capacity in soils to absorb this rainfall, which for many will be welcomed given our recent dry weather. In addition, a tornado threat may also develop in the vicinity of the effective front, but there is a lack of a surface low nearby driving stronger low level flow, which is reflected in the the low storm relative helicity values and poor streamwiseness.

The storms Saturday evening will move away with details in the forecast become fuzzy into early next week as successive convective events compound uncertainty and model consensus diverges. It does look like a mesoscale convective system (MCS) develops somewhere upstream of Iowa Saturday night and may move across some portion of the state late Saturday night into Sunday morning. After any storms with the MCS move out Sunday morning, it looks like we could stay capped through much of the day with warm and windy conditions, but this will depend on where the MCS tracks and any boundaries or convective debris left behind. Storms may develop in the LLJ over Iowa Sunday night, but a higher risk of severe storms and locally heavy rainfall may develop Monday afternoon and evening as low pressure and stronger forcing moves over Iowa. However, the ECMWF and CMC are slower than the GFS and this is also shown in the ensemble 500mb data as well. This could have storm potential linger into Tuesday. After the boundary does push through the state, whether Monday night or sometime Tuesday, cooler and drier air will move into the state along with less stormy conditions.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 610 AM CDT Fri May 15 2026

VFR conditions will prevail through much of today. Thunderstorms will develop in northern Iowa around 00z, moving east through the overnight and moving east of all sites after 08-10z Saturday morning. Severe storms are expected and may produce large hail and damaging wind gusts. Timing may be refined in future updates.

DMX WATCHES/WARNINGS/ADVISORIES

None.