086 FXUS63 KDMX 031938 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 238 PM CDT Fri Jul 3 2026 .KEY MESSAGES... - Thunderstorm chances continue at times late this afternoon and through the overnight hours. Damaging winds and heavy rainfall are the main concerns, although hail will also be possible with stronger storms. - Additional heavy rainfall today and tonight could lead to new or worsening flash flood conditions, especially in areas that received significant rainfall last night. - Scattered showers and non-severe thunderstorms possible on Independence Day, mainly over northern Iowa. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 233 PM CDT Fri Jul 3 2026 After what was a very wet night and morning for central Iowa, we are seeing a bit of a break in the activity today before more storms develop again overnight. The environment left over from this morning's storms is quickly recovering thanks to mostly clear skies and persistent warm, moist air advecting into the area. This will lead to more destabilization, generally along a mesoscale boundary with an instability gradient setting from west to east over central Iowa. There isn't much for synoptic forcing over Iowa this afternoon, but as we approach peak heating, convergence along the boundary may be sufficient to develop storms. The general timing for this initiation looks to be around 23z to 00z at the earliest, although short range guidance is a bit uncertain on when these diurnally driven storms will develop, if at all. Something to watch that's developing as this is being written, is the MCS currently over Missouri producing a cloud shield and likely limiting heating in Iowa. This could limit initiation later today. That said, this activity find enough lift to take off late this afternoon and into the evening, it will have access to 3000 to 4000 J/kg of CAPE, although wind shear will be modest around 30 kts. Therefore, severe weather is certainly possible if any stronger storms develop an organized updraft. Damaging winds and hail will be the main concerns, with a low risk for tornadoes given poor low level flow. Of similar concern will be the potential for heavy rainfall in a moisture rich environment combined with training storms over areas that had already received heavy rainfall last night. This could exacerbate ongoing flood conditions, or lead to new flooding in areas where soils are saturated from last night's rain (primarily over central into northeastern Iowa). As we get later into the evening, the 850 mb jet will begin to ramp up, nosing into southeastern Nebraska and southwestern Iowa. This will interact with the boundary draped across the region, developing storms to our west which are progged to grow upscale into a mesoscale convective complex. Expectation would be for this complex to ride along the nose of the low level jet and with the instability gradient, tracking eastward into Iowa. This system could bring some damaging wind gusts through the state overnight into early Saturday morning. Likewise, heavy rainfall would be likely with this system, potentially adding to the rainfall amounts from any previous convection. Like the earlier, diurnally driven storms, CAMs are struggling to get a handle on this complex, but it has been fairly persistent from run-to-run, just with differing paths and intensity. If no storms occur earlier in the night, it stands to reason there will be a pocket of untapped air over Iowa that this MCS could take advantage of, leading to a more intense system. Conversely, if convection is ongoing much of the evening, the atmosphere may be more worked over in central Iowa, pushing the system farther south. Therefore, like much of the activity this week, how this second wave plays out will be dependent on the first. Aside from the severe chances, this MCS will bring another shot of heavier rainfall, albeit more progressive than the earlier storms. This would be additive to any rain that occurs this afternoon. Total rainfall expected this evening may range quite a bit depending on if we get both waves, or just one or the other. That said, expectation is for at least an additional 1 to 2 inches of rain falling over most areas tonight, with some localized amounts of over 3 inches possible. A Flood Watch remains in effect through Saturday morning, and a number of area rivers continue to see rises today. For more information on the hydrological concerns, see the hydro discussion below. The overnight storms generally depart the area early Saturday morning, pushing the boundary to the south of Iowa. The upper level pattern will also be transitioning to more of a zonal flow, and losing some of the persistent low to mid level moisture advection as flow flips to more west and northwesterly through the day. That said, a shortwave aloft dropping out of Minnesota may still interact with the residual moist and unstable air mass in Iowa, producing some showers and thunderstorms in northern Iowa on Saturday. Fortunately, wind shear is negligible, meaning this activity would likely be pulsey and less organized. Therefore, the severe risk seems minimal on Saturday, again assuming the surface boundary pushes out of the area Saturday morning. If it doesn't, diurnally driven storms could once again develop over southern Iowa Saturday afternoon, but this seems like an outlier scenario. Long story short, while the picture is becoming clearer for Independence Day, make sure to keep an eye on the forecast and radar on Saturday, especially if you have any outdoor plans! && .LONG TERM /SUNDAY THROUGH THURSDAY/... Issued at 233 PM CDT Fri Jul 3 2026 Aside from a few scattered showers at times, we generally get a break from the persistent thunderstorm chances Sunday into Monday, as northerly flow and increasing pressure at the surface fully takes over influence of Iowa. Temperatures respond accordingly, with relatively cooler highs in the mid 80s. Widespread precipitation chances look to return through the middle of next week, but more on that once we are through the weekend. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1236 PM CDT Fri Jul 3 2026 VFR conditions currently prevail over the state today with mostly clear skies. Thunderstorms are expected to develop again late this afternoon and into the evening. Highest confidence for thunderstorm impacts tonight will be at KDSM and KOTM, although KFOD and KALO will be on the peripheries of this activity as well. KMCW is likely too far north for storms, but haven't entirely ruled out a more northerly solution so have maintained PROB30 mention. A period of MVFR cloud cover also looks to develop early Saturday morning. && .HYDROLOGY... Issued at 233 PM CDT Fri Jul 3 2026 In the short term, flash flood type concerns will exist with any heavy rainfall through Saturday, with the main risk in the flash flood watch area. Most likely issues would be ponding especially in towns and cities. Heavier amounts than expected may lead to flash flooding especially localized. River flooding is a longer term concern. Multiple river flood watches exist across the CWA. Those river forecast points are generally expected to rise near or slightly above flood stage. Given potential outcomes of rainfall into Saturday, confidence was below warning criteria. Existing river forecasts include 24 hrs of QPF. Basins that see higher rainfall than QPF may see higher rises than forecast, and basins that see lower rainfall than QPF may not see as high. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch through Saturday morning for IAZ023>028-033>039- 044>050-057>062-070>075-081>086. Extreme Heat Warning until 10 PM CDT this evening for IAZ084>086-092>097. && $$ SHORT TERM...Dodson LONG TERM...Dodson AVIATION...Dodson HYDROLOGY...Zogg
