textproduct: Des Moines

KEY MESSAGES

- Pleasant weather today.

- Scattered shower and isolated thunderstorm chances (10 to 20%) tonight. The Severe weather threat is very low.

- Strong to severe thunderstorms possible late Tuesday night and into Wednesday. A significant severe weather threat may develop over parts of southeast Iowa on Wednesday.

DISCUSSION /THROUGH SUNDAY/

Issued at 304 AM CDT Mon Jun 15 2026

Surface high pressure centered over southwest South Dakota and northwest Nebraska is ridged eastward into southwest Iowa early this morning. Light westerly wind to light and variable conditions have resulted from the high pressure ridging. A few passing mid-level clouds otherwise little sensible weather going on across the state outside of seasonably cool conditions with pockets of radiational cooling setting in.

The focus this forecast period revolves around two systems, with the first arriving tonight and a more significant system arriving late Tuesday night and Wednesday. Pesky upper level low pressure over Hudson Bay is beginning to retrograde and pivot back south/southwest this morning and will be over northeast Ontario on Tuesday. This system will rotate the aforementioned PV anomaly/short wave systems through the state.

The first short wave will arrive overnight tonight. This system will be moisture challenged as it passes across Iowa with the dry air currently in place and just meager moisture advection with the system that is mostly originating from the Pacific. Instability is also quite weak with MUCAPEs below 300 J/kg. Overall expect a few showers and perhaps a few instances of lightning.

A much more dynamic system will arrive late Tuesday night and into Wednesday. The low level jet (LLJ) will strengthen Tuesday night to 55-65kts ahead of the system and that will promote strong theta-e advection and moisture transport northward into Iowa. Tuesday evening storms over the Dakotas likely will weaken before reaching Iowa but new storm development is likely as MUCAPES rapidly increase to over 1000 J/kg after midnight and should promote new updrafts, especially near the nose of the LLJ where the speed convergence and forcing is the greatest. This is where the potential scenarios diverge a bit. If the instability and surface dew points arrive a bit early, the early morning convection could grow upscale and become surface based by mid Wednesday morning and race east into northern Illinois and could continue to be fueled by the easterly veering LLJ. That scenario could lead to a significant wind event developing as it moves east. The 0-3 km shear vector of 50-65 kts is worth noting for the potential for QLCS development, again, likely to the east of Iowa with the morning convection. Also worth noting that the layer supercell composites are pinging over the northeast half of Iowa at 12z Wednesday. Will any morning convection push an outflow boundary southward and impact afternoon instability across Iowa? That is the question though theta-e differences are near 30C which favors keeping early cold pools in balance and with the short wave arriving late morning and early afternoon, that would promote some north advancement of the the warm sector. The elevate mixed layer (EML) capping will arrive behind the morning convection. How long that remains in place will impact the later convective chances as well.

Scenario 2, the cold pool does not push everything south. In this scenario, a sharp surface based CAPE gradient is likely to develop over parts of central into east central Iowa and angling ESE. Numerous model guidance has surface wind from the southwest in the warm sector and from around 100 degrees north of the boundary. That is strong shear along the boundary though the warm sector wind typically doesn't promote tornadic activity over Iowa. In this scenario, the EML erodes with mid-level cooling and convective initiation begins. Initial supercells would be favored and the right mover motions are nearly straight east. That motion would move warm sector supercells across the boundary which could lead to enhanced vorticity ingestion, which could promote tornadic development before moving more into the cold side of the boundary. Supercells could deviate a bit right from the forecast Bunkers right mover motions and follow the instability gradient. Overall, the situation will be monitored closely and this system will start to move into the CAM domains later today, which will offer more guidance. Gusty to strong westerly winds are expected behind the system along with the potential for wrap around convection.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 635 AM CDT Mon Jun 15 2026

VFR conditions today and through most of the evening. A few showers and isolated thunderstorms are possible late this evening and overnight. The potential at any location remains low and only included Prob30 mention at KMCW and KOTM. Light wind this morning may become breezy from the west late this morning and into the afternoon. The wind will diminish again towards 00z.

DMX WATCHES/WARNINGS/ADVISORIES

None.