FXUS63 KDMX 041954 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 254 PM CDT Tue Aug 4 2026 .KEY MESSAGES... - Marginal Risk for severe weather this afternoon in southern Iowa. Damaging winds are the primary threat. - Heavy rainfall tonight with a band of 1-3" and locally higher amounts. Highest likelihood in southwest Iowa. - Below average temperatures the rest of the work week, followed by warming temperatures and storm chances. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 251 PM CDT Tue Aug 4 2026 Thunderstorm activity waned this afternoon with scattered showers festering in central Iowa. More uniform showers could be found along the main theta-e advection axis in Nebraska. A vorticity max will pivot around the broad trough over the northern US, which will reinvigorate the stalled front over western and northern Iowa this afternoon and into the overnight. A Marginal Risk for severe weather was added this afternoon across southern Iowa, mainly for wet microburst potential. Clearing in this part of the state has led to further destabilization with CAPE values exceeding 1000 J/kg this afternoon. Effective shear values of around 30kts orient along the front, favoring a line of storms, albeit broken from the weak updraft acceleration from poor lapse rates. Southeast Iowa presents the best environment for severe gusts due to the prolonged clearing, increasing theta-e differences in the lowest 3km. A Flood Watch was again considered on this issuance, but later decided against. Summary below: The LLJ will veer across the state tonight, with the front stalling across central Iowa. The nose of the LLJ will be somewhere between I- 80 and Highway 30. PWAT values will be around 2", warm cloud depths over 4000m, and instability profiles are skinny due to the deeply saturated profile. The mean wind is parallel to the stalled front, but there could still be a southern push as Corfidi vectors suggest established cold pools will dive southeast. This increases confidence that the heavy rain axis will be more south than deterministic guidance is suggesting. High confidence in the rain band having widespread 1-3" with localized amounts exceeding 5". HREF and REFS ensemble LPMM QPF illustrate those local QPF maxes, with the HREF more bullish in high QPF (>3") probabilities. REFS values are lower, likely due to placement uncertainty of the band. Current thinking is the HREF coverage of 4"+ amounts is too broad due to the amount of its members residing on the high end of the QPF distribution (FV3 and NAM 3km current and time-lagged). In addition to the uncertainty with QPF magnitude, the placement is in an area with antecedent conditions that work against flooding potential. The 40cm soil moisture is very dry, below 10% in most of western Iowa. Southern Iowa is below 20%. Mature corn crop will readily absorb rainfall in rural areas. Flash flooding risk is limited to urban areas that may be under the QPF max (4"+). Low confidence in rivers rising to high water levels in the National Water Model, as most high water potential is in eastern Iowa where soils are more moist. Thunderstorms will wane through Wednesday morning and the front will sink into northern Missouri, reigniting later Wednesday night when the LLJ returns. A Slight Risk ERO is retained across the south for the continued rainfall through Wednesday, but confidence is increasing in the Wednesday night QPF max residing outside of central and southern Iowa. && .LONG TERM /THURSDAY THROUGH MONDAY/... Issued at 251 PM CDT Tue Aug 4 2026 In the extended, temperatures will stay near to below average through the end of the work week and 90 degree highs will try to make a return over the weekend. The region will be locked in northwest flow which keeps thunderstorm chances in play. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1245 PM CDT Tue Aug 4 2026 MVFR cigs are returning with the rain in western Iowa, affecting KFOD first. A line of storms may form and move across southern Iowa, affecting KDSM within 4-6 hours, but confidence is only 30% due to the lack of clearing at the terminal today. Refined shower and storm timing and added in heavier cig/vsby restrictions for when storms peak in the overnight hours. Highest confidence in longer term impacts at KDSM and KOTM. Thunderstorms will last at KOTM through the morning with pockets of +TSRA likely and will add mentions in once timing of heaviest storms is better understood. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Jimenez LONG TERM...Jimenez AVIATION...Jimenez