textproduct: Des Moines

KEY MESSAGES

- Dense fog likely again tonight, mainly across central and eastern Iowa.

- Marginal risk for severe weather Friday and Saturday. Damaging winds are the primary threat and hail is more likely on Friday.

- Heavy rain with Marginal Risk EROs all weekend. Rain and storm chances linger for the remainder of the forecast.

SHORT TERM /THROUGH FRIDAY/

Issued at 141 PM CDT Thu Aug 6 2026

Fog took its time to lift today and clouds remained in its wake this afternoon. Highs were reduced to near 80 degrees, and the cooler temperatures and calm winds spell more dense fog tonight in central Iowa. Northern Iowa may see less of it this time due to more elevated winds.

Friday: Northwest flow will open up the state to a series of shortwaves for much of the upcoming forecast, the first of which will be on Friday. Lee cyclogenesis forms tonight and enhances the low-level jet in the Central Plains, pushing the moisture axis into Iowa on Friday morning. At the same time, a cold front will move in from the northwest, these two features intersecting through the day. The cold front may bring an existing MCS with it, although it will be contending with capping from the re-established EML. Most guidance has this early convection fizzling for this reason. The second window to watch will be in peak heating hours Friday afternoon. CAPE values over 2000 J/kg will be in play, but the magnitude alludes to the capping in place. If we get the fog tonight, warming will be delayed by it and the subsequent stratus, so the environment will depend on kinematics to overcome CIN. Q- vector convergence is strongest in northern and northeast Iowa, collocated with where fog is less likely to form. Convergence is primarily frontogenetical in central Iowa and confidence is lower in storm initiation. Once formed, storms will sink south- southeast into Iowa and reorient the instability axis for Saturday. Since yesterday, the upper jet will lag behind the front, so the deep- layer shear is lower: around 25-30kts. Its orthogonal orientation relative to the front will favor supercells. Current expectation is to have a limited amount of sustained supercells with most updrafts succumbing to the weak low level shear and dropping outflows quickly. Damaging winds will be the main threat with most storms and supercells will carry an elevated hail threat.

LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/

Issued at 141 PM CDT Thu Aug 6 2026

Saturday: The warm sector gradient orients northwest to southeast across Iowa, and extending further into Nebraska. The next shortwave will spawn an MCS on this gradient early Saturday with its remains entering Iowa by Saturday afternoon. It will be caught by the retreating surface front, the highest confidence in afternoon severe storms in southwest Iowa. The LLJ will intensify Saturday afternoon and overnight, igniting the elevated reflection of the front. It will veer east through the night and offer a chance for heavy rain in central and eastern Iowa, reflected by the Marginal ERO. PWATs will rise over 1.5" and the mean wind will point to the east, favoring some training on the flattening boundary. If storms lean more organized, training will happen less.

Sunday: While dependent on weather the previous two days, Sunday night looks representative of a Maddox frontal setup for heavy rain. With model simulations placing the front in southern Minnesota. At this range, due to cold pools from storms days prior, this QPF axis is possibly predicted to be too far north. PWATs will approach 2 inches and both the mean wind and Corfidi vectors mirror the front, meaning training is possible even with organized MCSs. It's worth monitoring trends to see if the front does indeed sink south into Iowa. Rain rate-driven flash flooding would become possible in urban areas.

The forecast beyond features northwest flow with relatively higher deep-layer shear in northern Iowa. This is due to enhanced flow across the Upper Midwest. Precipitation chances will gradually sink south through the week due to repeated storms shoving the boundary more into the ridge. Nearby instability will keep storms in play.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 647 PM CDT Thu Aug 6 2026

Areas of cumulus leading to MVFR ceilings at times are expected to fade over the next hour or two as the sun sets. While VFR conditions will return into the evening, this will be short- lived as stratus is expected to expand northward across Iowa after 06-09z, as well as patchy to locally dense fog. Confidence on exact visibility restrictions and ceilings remains low at this time, but the combination of the fog and low stratus will likely result in widespread IFR and periods of LIFR conditions until mid-morning. After ceilings lift and fog fades, showers and storms will be possible over northern Iowa and eventually further south towards KDSM and KOTM near the after the current period. PROB30 mentions have been added to the northern terminals in this issuance, though adjustments are likely given trends and evolving conditions over the next several hours. Light southwest winds will shift northwest after 18z behind the passing frontal boundary, which will sink southeast with time.

DMX WATCHES/WARNINGS/ADVISORIES

None.