textproduct: Des Moines

KEY MESSAGES

- A few severe storms in northern Iowa late this afternoon and evening with large hail, damaging wind gusts, and a tornado possible. Locally heavy rainfall is also possible in far northern Iowa.

- Next round of severe storms and locally heavy rainfall on Tuesday afternoon into night, especially central into southern Iowa.

- Additional rounds of severe storms and locally heavy rainfall on Wednesday (eastern Iowa) and again on Friday (much of Iowa).

- Warm and breezy today through Friday with highs in the 70s and 80s, then temperatures tumble into the 40s and 50s this weekend.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 318 PM CDT Mon Apr 13 2026

Today is the start of a busy, active stretch of weather with multiple rounds of severe storms and heavy rainfall potential through weeks end. The first round is setting up for later this afternoon into this evening over northern Iowa. Early afternoon GOES-East Day Cloud Phase Distinction has scattered low level cumulus clouds from Siouxland into northern Iowa with a fair amount of clearing south of these clouds in western Iowa. A warm front is where the clearing/scattered cumulus clouds are located from just north of Sioux City to north of Algona to north of Mason City. Forecast soundings initially show a warm capping layer aloft, which will prevent storm development. However, as the triple point/low pressure moves into northwest Iowa late this afternoon, these same soundings show weakening of the cap. This will allow any inhibition to be overcome and for surface based storms to develop in the vicinity/east of the triple point. Proximity soundings show 3000 J/kg or more of entrainment CAPE, more than ample deep layer shear, and steep lapse rates for severe storms. The hodograph is more linear given lack of backed surface flow so large hail and damaging winds are obvious concerns. Uncontaminated 0-1 km storm relative helicity is marginal at around 100 m2/s2, but with the triple point and warm front over our area, think a few tornadoes will be possible as the flow backs more locally ahead of these features that may enhance the low level flow and helicity. Looking at convective allowing model (CAM) guidance, this has been showing up in past runs of the HRRR along with the ARW cores developing over northwest into north central Iowa close to 0z/7pm this evening. Warn on Forecast (WoFS) is running over the area and the 18z paintballs shows initiation between 22-23z/5-6pm and potential for rotating storms in the vicinity of Spencer that then spreads east-northeastward. As one or more storms develop and move to the east-northeast, these should congeal into a line with the main hazards transitioning more to a large hail and damaging wind threat as the storms exit into northeastern Iowa by midnight. While quite limited, National Water Model forced HRRR has shown some rapid onset flooding potential in far northern Iowa near the Minnesota border, but as the hydro discussion outlines below this will be limited to urban areas. For areas outside of northern Iowa/south of roughly Highway 3, the forecast is expected to be dry. The exception, which is shown in the ARW and NAMNest, is the possibility of convection with a hail and wind threat that turns east- southeastward into the instability gradient. While not a likely scenario, it does exist.

Severe risks also exist on Tuesday and Wednesday with each subsequent round better determined after the first has occurred. For Tuesday, the boundary will slip into our forecast area with a weak surface low to the west of the state that moves in later in the day or at night. The front should be a focus for possible storm development mid to late afternoon, but there is a variety of times and locations for convective initiation as the location of moisture gradients, the low position, and wind fields all vary greatly amongst the CAMs. This plays a crucial role in what, if any, storms develop in the afternoon, their location and their hazards. While whatever threat develops and moves into eastern Iowa Tuesday evening, a strong low level jet will begin to move up into our area by late evening. This will bring renewed convection into southern and central Iowa by late evening through much of the overnight, which wanes into the daylight hours of Wednesday. The main hazards would be hail and wind.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Issued at 318 PM CDT Mon Apr 13 2026

As the western CONUS shortwave trough finally lifts into our region, expect a final round of storms across eastern portions of Iowa on Wednesday. Instability and shear parameter space looks favorable for strong to severe storms with large hail, damaging wind gusts, and tornadoes all possible. Further, the surface low and warm front could be over central Iowa and may aid in enhancing low level hodographs, but this is a detail to monitor versus be concerned about at this time horizon.

As Wednesday's strong synoptic forcing passes by, Thursday is looking like a more tranquil, dry day into Thursday night. However, the next amplified shortwave trough will be trucking towards the region taking on a neutral tilt. With a surface low and cold front moving through the region/state sometime on Friday with highs reaching the 70s and 80s, another round of strong to severe storms will be possible with this highlighted in the day 5 SPC outlook. As the storms move east of the state Friday night, colder air will wrap in behind the departing low and cannot rule out some snowflakes in northern portions of the state early Saturday. Temperatures will tumble into the 40s and 50s with breezy winds from the northwest on Saturday as well. Further, those with early season vegetation will want to monitor the forecast with sub-freezing temperatures forecast Saturday night/Sunday morning.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1110 PM CDT Mon Apr 13 2026

MVFR stratus and fog will again be possible across the north over the next 8 hours, have trended worse on conditions given conditions seen yesterday morning. Adjusted prob30 groups and added prevailing groups for showers and storms tomorrow afternoon. Highest confidence in storms at KALO. Additional storms possible near the end of the TAF period, highest confidence at KOTM at this time.

HYDROLOGY

Issued at 239 PM CDT Mon Apr 13 2026

Multiple rounds of seasonally moderate to heavy rain this week will lead to renewed flooding concerns. Presently the main concern will be possible renewed or additional river flooding.

Output from the GFS- and NBM-forced medium-range National Water Model (NWM) and the Hydrologic Ensemble Forecast System (HEFS) suggest the most likely scenario will be moderate to significant within-bank rises on many rivers and streams, especially across the southeast half of the CWA over the next week. A few locations may see minor river flooding as well. These rises will be due to the additive effect of multiple rounds of rainfall. If rainfall is higher than presently forecast then the risk of several locations seeing minor flooding and a few locations seeing moderate flooding will increase.

Flash flooding is less of a concern than river flooding, however the risk is nonzero. The most likely scenario will be ponding of water or low-end flash flooding especially in urban areas or areas that receive repeated heavy rainfall over a relatively short time period.

DMX WATCHES/WARNINGS/ADVISORIES

None.