textproduct: Des Moines

KEY MESSAGES

- Two rounds of severe storms possible today. 1) Large hail the main hazard as storms lift from western Iowa this morning into northeastern Iowa early this afternoon. 2) Storms form this afternoon ahead of a cold front with hail, tornadoes, and strong wind potential.

- Locally heavy rainfall could lead to isolated flash flooding with this risk highest in urban areas.

- Cooler, blustery on Saturday. A bit milder, less wind on Sunday.

- Increases chances for rainfall and storms mid into late next week.

SHORT TERM /THROUGH TONIGHT/

Issued at 345 AM CDT Fri Apr 3 2026

Early morning GOES-East upper level water vapor imagery shows a cyclonic spin over the northern Rockies while the system responsible for our stormy Thursday weather has lifted over Lake Superior and vicinity. While this flushed out the moisture in the atmosphere with now much lower dewpoints and precipitable water (PWATs) values, this will change quickly today as surface low pressure over western Kansas lifts to near St. Joseph, MO by mid-afternon to northeastern Iowa late this evening. Ahead of this surface low, which will be relatively steady state in its pressure around 1000mb through its track, moisture transport and recovery will be impressive ahead of it. This is due to strong low level warm air advection (WAA) aided by a 40 to 45 knot low level jet this morning that weakens into this afternoon. As this WAA occurs, instability will be building above an elevated warm layer with MUCAPE values up to around 1000 J/kg possible with mid-level lapse rates around 7 C/km. Effective shear of 40 knots or higher is forecast with much of this driven by speed shear within the CAPE layer. With a rather straight hodograph, large hail will be the main concern as storms develop over western Iowa in the WAA wing by 9 or 10 am this morning and lift northeastward into north central and northeastern Iowa by early this afternoon.

Attention then turns to the afternoon storm potential. A warm front will be lifting northward into southern Iowa with a temperature bifurcation from northwestern Iowa where temperatures will struggle to reach 40 degrees to southeastern Iowa where highs will peak in the 70s. Dewpoints in the warm sector are forecast well into the 50s and even low 60s. Forecast soundings show the inversion persisting much of the day in the warm sector with HREF cloud cover showing scattered pockets of insolation. This along with the WAA regime will be working to weaken the inhibition/capping, but it seems storms development, at least surface based, will have to wait until the surface cold front reaches any given location in central and south central Iowa this afternoon. Surface instability just ahead of the front will grow to between 1500 to 2000 J/kg with effective inflow layer shear of 30 knots and modest low and mid-level lapse rates of 6 C/km. Cloud bases/LCLs will be low and the surface low will contribute backed surface flow with hodographs having an ominous curvature on first glance with impressive 0-500m and 0-1km storm relative helicity values of around 200 m2/s2. However, the hodograph is more messy in the 1-3 km layer and this may have a negative effect on tornado potential. Beyond the tornado potential, large hail will be a concern, especially with any discrete, isolated cells. Wind threat also remains, but may be diminished some by the low level (surface to 1.5km) saturation shown in the soundings resulting in downdraft CAPE values under 600 J/kg.

So, where does the uncertainty lie in this afternoon's forecast? In no particular order...1) The amount of insolation/sunshine. Less sunshine may result in storms being elevated (favor hail/wind risk) versus surface based (higher tornado risk along with hail and wind). However, even an hour of sunshine has proven to be more than enough with early/late season severe weather setups for tornado potential. Storm coverage may be limited, at least initially, though the front should be sufficient for slab lifting to get storms going, especially into eastern Iowa as the storms congeal into more of a line. 2) The messy hodograph, especially the aforementioned 1-3km layer. While this is shown in multiple model forecast soundings, if the hodograph ends up being less messy and 'smoother', this may lend to a higher tornado potential, which is something we and SPC will be watching for if parameters align 'just wrong'. 3) The track of the surface low, which will dictate the area of highest severe weather concern. There is generally good agreement in model placement through early afternoon, but spread grows into this evening.

On the rainfall and potential flash flooding front, many areas over the last 24 hours have received three quarters of an inch across central Iowa with narrow bands of 1.5 to 2 inches, per radar estimates. NASA SPoRT relative soil moisture (RSM) in the 0-10cm layer (important for rapid onset responses) show above the 80th percentile roughly along and north of Highway 20 across much of Iowa with an area in northeastern Iowa above the 95th percentile. Heavy rainfall parameters are noteworthy for early season with forecast precipitable water values near or above the DVN RAOB climatological max, which is around 1.2 inches. Warm cloud depths are seasonally high around 3000m. While the 850-300mb flow will be fast, it will be the potential for two rounds of storms that flash flooding could become a concern. Earlier Canadian model runs and MPAS members and 6z HRRR were pegging northeastern Iowa with 2-3.5 inches of rainfall by Friday evening, which lined up unfortunately well with the more saturated soil. In coordination with WPC, a slight risk was introduced over parts of our eastern forecast area, including Waterloo/Cedar Falls and Marshalltown, into parts of northeastern and east central Iowa. This slight risk lines up with the northern extent of the late Thursday update from the National Water Center in their flood hazard outlook. Looking at the latest Canadian runs, it has shifted its heaviest rainfall into south central Iowa with 2-3 inches so will need to monitor trends in rainfall location since it may be shifting. The highest flash flood risk will likely be in urban areas.

As the low lifts into Wisconsin overnight and the cold front moves through the state, this will end the risk of severe storms and heavy rainfall from west to east this afternoon into this evening.

LONG TERM /SATURDAY THROUGH THURSDAY/

Issued at 345 AM CDT Fri Apr 3 2026

Moisture will try to wrap back into Iowa as the surface low moves away from Iowa with spotty light rain or snow showers. Gusty winds from the northwest will prevail and increase through the daytime Saturday with sustained winds peaking at 20 to near 30 mph and gusts in excess of 35 or 40 mph. Highs will range from the low 40s over northern Iowa to the low 50s over southern Iowa, which will be about 5 to 10 degrees below normal for early April. High pressure will transit the region on Sunday bringing lighter winds. On Monday, modest low level thermal lift and coincident QG convergence may allow for an area of light precipitation into parts of western Iowa. Stronger WAA is forecast on Tuesday, which will bring in warmer air by Wednesday ahead of a front. By late next week, the pattern looks more active again as the front slowly moves through the state. While there are very low severe probabilities in the AI/ML, will also need to watch heavy rainfall with deterministic, ensemble, and AI solutions showing 1-3 inches in varying portions of Iowa.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 608 AM CDT Fri Apr 3 2026

MVFR ceilings were common across central Iowa early this morning with restrictions forecast to lower at times as showers and storms move through at intervals today. One round of showers and storms is expected to lift over FOD, DSM, MCW, and ALO this morning into early this afternoon. Confidence is highest in these showers and storms at all but DSM. Another round of storms is expected later this afternoon and evening with refinement of PRBO30 and inclusion of TSRA as prevailing in future updates. More persistent IFR or lower ceilings are expected tonight as the storms and cold front departs to the east. Winds will become from the northwest and turn gusty by the end of the period.

DMX WATCHES/WARNINGS/ADVISORIES

None.