textproduct: Des Moines

KEY MESSAGES

- Early morning thunderstorms, some severe, are expected this morning, then scattered thunderstorm chances last through this afternoon and evening. Damaging winds are the primary threat with isolated large hail, locally heavy rain, and a tornado or two also possible this morning.

- Additional thunderstorms are possible overnight and early Friday morning with some amount of uncertainty due to the evolution of this morning's storms. These storms could be severe with pockets of heavy rain as well.

- The pattern remains active with storms chances through the weekend and early next week.

SHORT TERM /THROUGH FRIDAY/

Issued at 302 AM CDT Thu Aug 13 2026

Thunderstorms are expected yet again this morning, once again with severe potential. Compared to the past several nights, this looks like the 'best' setup for severe thunderstorms across western and central Iowa. Storms have formed driven by pronounced shortwave energy that has been notably lacking the past several mornings and are making their way east across Nebraska. Mesoanalysis suggests a strong cape gradient across the state which the line which the line will ride on. At the same time, there is ample shear across the state. One of the failure modes for previous nights would be the low level jet (LLJ) being farther to the south than guidance suggested. Given the better synoptic forcing, there is less reliance on the LLJ for this round of storms. There are still some questions about the strength of the MCS as it moves across the state. Radar trends show new updrafts forming in front of the main MCS and the 05z HRRR shows a 'one-two punch' with these updrafts growing upscale quickly before being overrun by the main MCS. If the updrafts out ahead do form into another line, this will lessen the blow of the MCS as it moves into the area and gets overrun. However, if these updrafts prove to be transient and we only see the main MCS, the potential ceiling is much higher in terms of our severe weather threat. Damaging winds are the primary threat once again, as with isolated instances of large hail and locally heavy rainfall, especially over any built up cities or towns. There is also a low QLCS tornado potential, though there is high uncertainty on the location of where the QLCS tornado threat is highest and this is further complicated by the potential for two lines. Should this MCS take a classic bowing shape, the northern side of the bow would be favored for QLCS spinups given the orientation of bulk shear vectors relative to the MCS itself. Otherwise, the threat will remain lower pending storm interactions. As for the heavy rainfall threat, this line should be fairly progressive through the morning hours. Locally heavy rainfall is still possible and flash flooding would become a concern over cities and towns where drainage is not as good.

Once the MCS clears our area which looks to be around the early afternoon hours, most areas should remain dry, although some guidance hints at lingering showers and storms in north central Iowa on the warm air advection wing, which leads us into tonight. Guidance is still rather split on how everything is handled Thursday night into Friday. Compared to previous runs, guidance is starting to trend later with with warm air advection precipitation. Some guidance suggests more robust convection earlier on, while other solutions are more showery through part of the night. A lot of this hinges on what our MCS does with the boundary currently analyzed across Missouri. There is a solution where the outflow from this morning's MCS will counteract that boundary moving north into Iowa, which would have further implications on convection overnight. If the boundary remains farther to the south, anything that forms over Iowa would be more stable and the severe threat would be rather low. There are other solutions where the boundary could make it into Iowa and, paired with better forcing, some level of severe potential would exist. We are expecting showers and storms even if they are not severe and rain amounts could start to add up, making flash flooding a concern. See the HYDROLOGY section for a few more details.

Following this warm air advection today, highs will once again poke up a bit - into the mid to upper 80s across southern and central Iowa (pending cloud cover clearing) with the mid to upper 70s farther north where scattered precipitation is expected throughout the day.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 142 PM CDT Wed Aug 12 2026

Overnight convection lingers into Friday morning with continued hydro concerns into the day. The pattern remains active through the weekend and upcoming week as wave continue to ride across the thermal ridge in this "ring of fire" set up. Repeated rounds of convection will rely on earlier rounds for both placement and strength. A few lulls in convection are possible next week, but timing out which days this may occur is difficult at this time range.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1133 PM CDT Wed Aug 12 2026

Primarily VFR conditions prevail this evening, although sporadic MVFR ceilings have occurred with patchy stratus. These conditions will generally persist through the morning, although a shallow fog may also develop at times. As we get closer to day break, there is high confidence that a thunderstorm complex will pass through the area, potentially impacting all sites. All sites may be impacted, but KDSM has the highest confidence with an arrival around 12z for that terminal. Strong winds and heavy rain may accompany the main line of storms. The rest of the sites remain on the fringes, but will likely see rain or storms as well. Low clouds then follow this system, keeping at least MVFR conditions over Iowa through the day Thursday. More scattered showers and storms are possible Thursday afternoon.

HYDROLOGY

Issued at 302 AM CDT Thu Aug 13 2026

Pwats of 1.5 to 2" today become largely over 2" on Friday, peaking near 2.5" by Friday evening. These will be paired with warm cloud depths, several rounds of rain, and the potential for training storms, and 1-2" per hour rain rates or more with thunderstorms. Although there remains some uncertainty with the corridor of highest rain amounts today through Friday, west central Iowa in particular has the potential to see some excessive rainfall where rainfall amounts may start to reach towards 3-5" or more. Similar rain amounts may start to add up through portions of central and then east central Iowa into Friday morning and then evening with subsequent rounds of rain and many models are hinting at some localized amounts even higher. A Flood Watch for Flash Flooding was hoisted that may have a wider coverage area than needed, but with some lingering uncertainty in the exact placement of highest rain amounts, wanted to make sure the watch covered the potential different threat areas which range from southern to central Iowa to central to north central Iowa. Central Iowa does appear the most likely regardless from around the I-80 to Highway 20 corridors. The main concerns with the excessive rain amounts are flash flooding, especially in urban and poor drainage areas, though some rises on area rivers and streams is likely.

DMX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Friday afternoon for IAZ023>028-033>039- 044>050-057>062-070>075-081>086-097.