textproduct: Des Moines

KEY MESSAGES

- Strong to severe storms possible late tonight with very large hail possible.

- Strong to severe thunderstorms into Wednesday with the primary focus over the eastern half of the state. Very large hail, damaging winds and a few tornadoes are possible.

- Strong and gusty winds possible at times on Wednesday.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 337 AM CDT Tue Jun 16 2026

Strong upper level short wave moving into the area early this morning. This system has PV 1.5 pressure surfaces approaching 500 mb. This system was mostly moisture deficient though it was able to create a few showers and embedded thunderstorms with precipitation amounts of a few hundredths of an inch in central Iowa. Any lingering precipitation will be moving out of the are over the next few hours. High pressure ridging will move across the area today though northwest wind will be breezy due to boundary layer mixing and may result in gusts of 20 to 30 mph this afternoon.

The primary focus this forecast period remains tonight into Wednesday. Relatively little change in the overall setup with temporal and spatial consistency occurring. A very strong low level jet (LLJ) of 65 to 70 kts will lift into Iowa after 06z and bring tremendous theta-e advection into the state. The one change here the LLJ will be arriving earlier into the mid-Missouri river valley and would support the storms moving southeast through South Dakota and may maintain their strength into Iowa. Note, 24 hrs ago, there was more uncertainty of the LLJ arriving in time to accomplish this. In addition, the strong speed convergence at the nose of the LLJ will support near storm development over central to northern Iowa. These initial storms will be elevated but with good speed shear through the storm level of 50+ kts, storms will quickly become organized and evolve into supercells. Very large hail will be possible. In addition, there are some hints that this could become Gravity Wave Associated Convection that could lead to a damaging wind threat as well despite the elevated nature of the storms due to the subsidence portion of the gravity waves. Currently targeting 10-12z for convective initiation of new development. These storms will move off to the east by mid-morning.

Several aspects a play for later morning and afternoon redevelopment. The warm sector is still expected to lift into Iowa, roughly from near Des Moines and east to southeast from there. Uncertainty remains on the redevelopment directly on this boundary as the elevated mixed layer moves into the area behind the earlier morning storms and that will cap surface based convection for awhile. In addition, the 125kt upper level jet is situated nearly on top of and perpendicular to the surface boundary. This would place the left exit region of the upper jet on the "cool" side of the boundary and the subsidence portion of the jet over the warm sector. This may be part of the reason model guidance is delaying the warm sector initiation until mid to late afternoon and favoring more development north of the warm front. Should a supercell develop near the warm front, the tornadic potential may become high with storm inflow relative helicity over 500 m2/s2. The more favored region for this to occur is over the SPC SWODY2 moderate risk region over nrn Illinois and Indiana but the initiation zone could be further west. The primary line activation has been trending a bit south and mostly south of the forecast area. Finally, don't sleep on the afternoon storms closer to the upper low across Minnesota and northeast Iowa. Rotating storms and a sneaky tornado potential may occur with these storms and may clip north central Iowa.

Finally, synoptic wind is the other consideration for Wednesday. Gusty south wind may approach 40 mph over southern Iowa Wednesday morning. Strong winds are also possible across much of the area Wednesday afternoon after the boundary passes with gusts of 40 to 50 mph possible.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 228 PM CDT Mon Jun 15 2026

Very early Wednesday morning the surface low will make it to northern Iowa, moving roughly the northern half of the state through the morning hours. SPC has added a marginal (level 1 of 5) risk for these storms early Wednesday morning, but noted that a portion of the risk area within Iowa may have a pocket of higher threat to be assessed. As it stands, a robust low level jet (60+ kts) will stretch across the plains and nose into northwest Iowa overnight, pulling moisture into the area before shunting east through the morning. A plume of 1500-2000+ J/kg MUCAPE reaches Iowa with storms likely to move east along the gradient through the morning. There is the potential that storms are able to grow upscale as the move into Iowa and encounter the better instability, fueled by the low level jet as they race east. Additional storm develop is expected along the boundary in southeast Iowa in the afternoon as daytime destabilization increases instability. The primary uncertainty is where this afternoon redevelopment sets up, hinging heavily on the path and strength of the early morning storms and associated outflow boundaries.

Strong environmental winds are expected Wednesday late afternoon into evening as storms push east with stronger subsidence, cold air advection, and a tight pressure gradient on the back side of the system as it departs. Soundings indicate 30-45+ kts through the mixed layer behind the departing system on Wednesday which may translate to 30-40+ mph gusts at the surface, especially across northern into central Iowa. Northwest flow keeps the area seasonably cool through the end of the week and into next week with highs in the upper 70s to low 80s. There are also repeated precipitation chances through the rest of the forecast period. A weak wave will likley bring additional showers and thunderstorms to the area on Thursday. Then a more robust system develops across the midwest on Saturday and Sunday. As we look ahead into next week the CPC notes continued cooler than average and higher precipitation than average through the 8-14 day outlook.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 635 AM CDT Tue Jun 16 2026

Gusty northwest wind today with gusts over 25 kts possible at times, especially near KMCW/KALO. A brief period of MVFR stratus at KMCW and it will be close to KALO. Did not include at KALO at this time as it appears to pass just north but will update if the trajectory changes. Otherwise VFR today into this evening along with diminishing wind late this afternoon. Thunderstorm chances arrive late tonight and include Prob30 mention at most sites except KOTM. The wind will become south/southeast overnight.

DMX WATCHES/WARNINGS/ADVISORIES

None.