textproduct: Des Moines

KEY MESSAGES

- Widespread light to moderate rain this evening with a few scattered storms possible south. A few storms may have small hail and gusty winds. Prolonged rainfall tonight could lead to rises on smaller rivers and basins.

- More shower and thunderstorm chances expected later Saturday into Sunday. Severe weather threat looks low, but more rainfall will continue to add water to rivers.

- Active weather continues with several rounds of rain and storms later Sunday into next week. Severe weather and heavy rainfall will be possible at times with these storms.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 246 PM CDT Thu Apr 9 2026

Rain and some isolated thunder has already started to impact portions of south central Iowa early this afternoon, as warm, moist air overruns the cooler low level air mass over Iowa. The surface boundary is currently draped over northern Missouri into central Illinois, and should generally remain south of the state through the entirety of the afternoon and evening. The 850 mb boundary, however, will intrude farther into the state overnight ahead of a shortwave passing to our north. This will allow for a healthy push of low- to mid-level theta-e advection and broad scale ascent over the stalled surface boundary to our south. Widespread rain and occasional thunderstorms will be the net result from this setup, impacting much of central and southern Iowa through the afternoon and into the evening hours. Weak elevated instability will be present with this activity, primarily over southern Iowa and southwestern Iowa where thunder will be more likely. Based on recent data, agree with the overnight shifts synopsis that the severe weather threat looks low, but a stronger storm can't be completely ruled out. The limiting factor to strong storms this afternoon and evening will be the lack of instability. With the surface boundary generally remaining to our south, any storms will be elevated and only have access to roughly 500 J/kg of most unstable CAPE, which will be primarily over southwest and southern Iowa. Wind shear will be sufficient for organized convection, assuming stronger updrafts can develop. However, with the broad synoptic lift, warm air advection aloft and a healthy surge of moisture, soundings show very saturated profiles with poor mid-level lapse rates, implying that updrafts would likely be weak and short-lived as they struggle to find a source of inflow. If any stronger storms do develop, likely in southern Iowa, gusty winds and hail would be the primary concerns. Even then, with such weak CAPE, and warm, saturated profiles, large hail will be difficult to come by.

While this environmental setup doesn't necessarily favor severe weather for our area, the stout low level jet and moisture transport into the area does rises some concern for heavy rainfall as it moves through. Precipitable water (PWAT) values will be nearing the climatological max of 1.19" for April. Modeled PWATs from the GFS and RAP range from 1.00" to 1.15", emphasizing the moisture available. This moisture will be fueled by the increasing LLJ this evening, before the shortwave pushes the moisture southeastward early Friday morning. Forecast rainfall amounts are generally around an inch to inch and half for much of the area and rates don't appear overly high (generally around 0.25" to 0.50" per hour) which should help minimize flash flooding concerns. However, as suggested in the prior discussion, high resolution models do suggest there could be a narrow corridor of higher rainfall amounts just from the prolonged nature of the rainfall. HREF probability matched mean QPF output through Friday morning paints this swath roughly around the Interstate 80 to US Highway 30 corridors, with a bullseye of 3"+ rainfall. If this falls in the wrong basins, this may lead to some localized stream flooding. More on the hydrological/river concerns in the hydro section.

By Friday morning, the shortwave will have pushed the surface and elevated boundaries to our south and east, leaving Iowa with a period of high pressure and drier conditions through Friday. Temperatures will remain mild with skies clearing out in the afternoon.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 246 PM CDT Thu Apr 9 2026

Friday's dry spell will be relatively short-lived, as the upper level pattern transitions to a southwesterly flow regime. This will open the midwest up to a strong gulf moisture stream, leading to multiple days of rain and thunderstorm chances. The first, and most immediate, of these chances will begin later Saturday as the gulf moisture initially arrives. Recall the climatological max PWAT values for of around 1.18", as this gulf moisture stream arrives, the GFS forecast PWAT values will skyrocket up to near 1.50" Saturday into Sunday, which is more comparable to values we would typically see in the summer months. Fortunately, there won't be any robust large-scale features accompanying this moisture plume Saturday into Sunday, meaning most of this precipitation will be driven by low level theta-e advection and a rather strong low-level jet. With the weaker forcing, QPF amounts at this time range don't look overly concerning, generally around a half inch to an inch. Likewise, there will be minimal severe weather threat, given the lack of any strong kinematics or even thermodynamics. Therefore, aside from occasional thunder, the main concern this weekend looks like it will be yet another widespread heavy rain event and more liquid routing into our rivers and streams.

More rain and thunderstorm chances continue intermittently Sunday through the beginning of next week with severe potential throughout that period. There has been quite a bit of variability from Sunday and beyond given the lack of any prominent synoptic features until around the Tuesday into Wednesday timeframe. Therefore, the broad takeaway at this time is an active pattern with some severe weather potential continuing into next week. Aside from the precipitation, temperatures also warm quite a bit into early next week as this pattern advects warmer, moist air up into the state.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1224 PM CDT Thu Apr 9 2026

Rain has started to spread across southern Iowa early this afternoon, impacting KOTM and KDSM within the next few hours. This rainfall is expected to persist and expand through the rest of the afternoon and evening, impacting all sites at some point through the next 12 hours. A few thunderstorms are also possible, mainly over southern into central Iowa, but aren't expected to be widespread or persistent. Therefore, have only included PROB30 mention for the most likely period at KDSM and KOTM. MVFR to IFR visibilities will accompany this activity through the evening and early morning hours before drier air begins to improve ceilings through Friday morning.

HYDROLOGY

Issued at 248 PM CDT Wed Apr 8 2026

Rainfall tonight into early Friday morning will generally be in the 0.5" to 1.5" range, with some locally higher amounts of 2 to 3" rainfall possible. The bulk of the rainfall will be over southern into central Iowa, which is where capacity is the best. While flash flooding is not anticipated, local river rises are possible, especially if this heavier swath falls over any smaller creek basins. Therefore, while the risk for flooding isn't high, the location of the heaviest rainfall will need to be monitored this evening. As we get into the weekend, more widespread rainfall is possible Saturday into Sunday, with forecast amounts generally around an inch or less. The current location for the highest QPF is currently over western Iowa where rivers and soils have more capacity, but will want to watch for an easterly shift closer to areas that have less capacity. Either way, rain on Saturday into Sunday will set the stage for what's expected to be an active week next week. QPF amounts and locations next week are still uncertain, but the wetter trend with successive rain events certainly raises concerns for increased river levels next week.

DMX WATCHES/WARNINGS/ADVISORIES

None.