411 FXUS63 KDMX 261139 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 639 AM CDT Sat Jul 26 2025 ...Updated for the 12z Aviation Discussion... .KEY MESSAGES... - Showers and thunderstorms continue across southern Iowa this morning, tapering off by midday. Heavy rain with pockets of 3+" possible. - Becoming hot and humid Sunday and Monday. Heat index of 105+ expected for much of the area both days. && .UPDATE... Issued at 234 AM CDT Sat Jul 26 2025 Showers and thunderstorms across northern Missouri have started to fill in early this morning and expand into southern Iowa along the plume of moisture and on the nose of the increasing LLJ. The severe threat remains quite low with very little available shear. And while a stronger gust might be possible from collapsing cores, with deep warm cloud layers the temperature differential is likely not going to be enough for anything substantial. Of greater concern is the heavy rain threat across southern Iowa with PWATs of 2-2.5" through this morning. 1-3" with pockets of 3-5+" are certainly possible, especially towards southeast Iowa. Activity tapers off towards midday with the rest of the afternoon mainly dry across the area. Some afternoon redevelopment is possible, but at this time this looks most likely just southeast of the area. By Sunday high pressure, and therefore heat, begin to build across the area. There is more than sufficient moisture in place with dewpoints of 75-80F likely, coincident with afternoon temperatures in the low 90s. This will send the heat index into the 100-105+ range across much of the area, prompting an extreme heat watch. Monday looks even warmer with the heat index reach 105-110+ and expansion of heat watches/other headlines are likely. The main area of uncertainty in temperatures is the possibility for convection with a shortwave passing across northern to central Iowa. Associated cloud cover may dampen temperatures a bit, however timing also looks to be later in the evening per recent guidance which may reduce any impacts. With this uncertainty, will reevaluate on the day shift. In any case, the heat Sunday and Monday will be some of the warmest of the season and care should be taken to keep cool and safe. && .DISCUSSION... Issued at 247 PM CDT Fri Jul 25 2025 Showers and isolated thunder over southern Iowa are the first of what will be intermittent shower and thunderstorm chances lasting through the evening. These chances will spread northeastward through the evening bringing the potential for more heavy rainfall to the area. Fortunately most of the rain last evening stayed outside the forecast area so soils aren`t as primed as what was anticipated this time yesterday. However, still anticipating some potential for flash flood impacts over southern Iowa, primarily in urban areas should prolonged heavy rain occur over the same area. Rainfall amounts will generally be around 1 to 3 inches, with isolated pockets of 4 inches or more certainly possible in some locations over southern into southeastern Iowa. Of similar concern will be a lower confidence but potentially impactful secondary band that develops slightly farther north in a few of the short range models. This would put a line of slow moving, training storms over central into north central Iowa, which is an area that received heavy rainfall earlier in the week. Likewise, rivers in these areas are already running at increased flows as water continues to route southward from rain this week. Should this band of 1 to 3 inch rain fall over one of these basins, the additional runoff could exacerbate conditions on the rivers, as well as lead to localized flash flooding as the water works it`s way through the system. Similarly, any heavy rainfall over urban areas could cause flash flooding and ponding on roadways. Again, this is a lower confidence scenario as most of guidance keeps the heaviest rain over southern Iowa where rivers are less aggravated, but certainly something to keep a close eye on. If this band displaces even farther north where flood warnings and watches are already ongoing, particularly on the Iowa and Cedar Rivers. The Des Moines River basin is also running at increased flow and could be impacted. Beyond the heavy rainfall and flash flooding risk, there remains a low chance for a few stronger storms, particularly in southern Iowa. The main threat with these storms will be strong winds as rain falls and the downward mass flux produces increased outflow from the storms. The storm prediction center currently has a marginal risk for severe weather just south of the forecast area and barely clipping our southeastern counties, but gusty winds are possible farther north of this area as well. Precipitation lingers into Saturday morning but should mostly wrap up through mid-day. Some guidance suggests isolated redevelopment in the southeast Saturday afternoon, but this will be fairly sporadic. The next hazard on deck is the hot and humid conditions that develop Sunday into Monday as thermal ridging/warm temperatures aloft leak eastward into the forecast area. Highs Sunday and Monday will be in the low to mid 90s, with dewpoints pushing the upper 70s to near 80 in some locations. This would push heat indices into the 105 to 110 range, likely warranting heat headlines on Sunday and Monday. Monday is currently forecast to be the warmest day, however, guidance has begun to key in on a shortwave dropping southward into the forecast which could impact high temperatures on Monday. This wave may also bring some severe potential to the area, with SPC pulling the marginal risk for severe weather. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 639 AM CDT Sat Jul 26 2025 Patchy fog has developed across northern Iowa, bringing IFR to LIFR impacts to northern sites KFOD/KALO with recent improvement at KMCW. This is expected to diminish in the next 1-2 hours. Meanwhile showers and thunderstorms have expanded across southern to central Iowa with impacts at KOTM and nearing KDSM. These will taper off through the morning with improvement to VFR conditions by midday. && .HYDROLOGY... Issued at 247 PM CDT Fri Jul 25 2025 With upcoming heavy rainfall in the south this evening, and the potential for a secondary band of heavier rainfall slightly farther north in the area, there will be a risk for additional impacts on area rivers this evening into Saturday. Basins of greatest concern will be the Iowa and Cedar River basins, which already have multiple sites approaching minor flood stage. Additional heavy rainfall of 1 to 3 inches within these basins could compound with the already elevated river levels and exacerbate flood concerns. Similarly, the Des Moines River basin is running at elevated levels, although no sites are currently expected to approach flood. This could change if the heavier band occurs. The Cedar River basin is at a lower risk of being directly impacted by this band, but is only slightly displaced from the expected area. The Iowa River basin and Des Moines River basins being farther south will be at a greater risk for being impacted by this band, which could push sites into flood stage that weren`t previously expected, especially those between the Highway 30 and Interstate 80 corridors. Urban areas will also be at risk for flash flooding, especially as runoff routes into already elevated streams. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch through Saturday morning for IAZ059>062-071>075- 081>086-092>097. && .DMX WATCHES/WARNINGS/ADVISORIES... Extreme Heat Watch from Sunday afternoon through Sunday evening for IAZ004>007-015>017-023>026-033>037-044>049-057>062- 070>075-081>086-092>097. Flood Watch until noon CDT today for IAZ059>062-071>075- 081>086-092>097. && $$ UPDATE...Hagenhoff DISCUSSION...Dodson AVIATION...Hagenhoff HYDROLOGY...Dodson